Radiology of the thorax

Kate Bradley

doi:10.22233/9781910443187.5

British Small Animal Veterinary Association , 109 (2013); https://doi.org/10.22233/9781910443187.5

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Radiology of the thorax

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Author: Kate Bradley
From: BSAVA Manual of Canine and Feline Radiography and Radiology
Item: Chapter 5, pp 109 - 175
DOI: 10.22233/9781910443187.5
Copyright: © 2013 British Small Animal Veterinary Association
Publication Date: January 2013

Abstract

There are many indications for thoracic radiography, both for the diagnosis of intrathoracic disease and as a means of screening to determine the extent of systemic diseases. This makes it an essential technique in the clinical investigation of many animals. However, despite the frequency with which thoracic radiographs are taken, the thorax remains one of the most challenging areas in veterinary radiography, in terms of the technical aspects of obtaining a diagnostic image and the subsequent radiological interpretation. A combination of an optimal radiographic techinique and a logical approach to interpretation will maximize the clinical information that can be gained from thoracic radiographs. General anaesthesia is commonly used, eliminating any resistance of the part of the animal to optimal positioning. A thoracic radiographic investigation should comprise at least two views: usually a lateral recumbemt view and either a DV or ventrodorsal (VD) view. There are many potential pitfalls in the radiological interpretation of thoracic radiographs. This chapter looks at Thoracic masses; Lungs; Heart; Pulmonary vasculature and great vessels; Pleural space; Mediastinum; and the Oesophagus.

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Figures

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5.1

It is important to obtain two, usually orthogonal, views for lesion localization in thoracic radiography. (a) DV view of the thorax of a cat with increased soft tissue opacity over the cranial cardiac silhouette and adjacent lung (arrowed). (b) The lateral view demonstrates that this change is actually extrathoracic and is due to a dorsally located subcutaneous mass (arrowed). © 2013 British Small Animal Veterinary Association

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5.1 It is important to obtain two, usually orthogonal, views for lesion localization in thoracic radiography. (a) DV view of the thorax of a cat with increased soft tissue opacity over the cranial cardiac silhouette and adjacent lung (arrowed). (b) The lateral view demonstrates that this change is actually extrathoracic and is due to a dorsally located subcutaneous mass (arrowed).

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5.2

Patient positioning for a right lateral recumbent view of the thorax. (a) The forelimbs should be pulled well forward and the sternum elevated so that it lies at the same height as the spine. (b) The X-ray beam is centred at the caudal aspect of the scapula. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2013 British Small Animal Veterinary Association

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5.2 Patient positioning for a right lateral recumbent view of the thorax. (a) The forelimbs should be pulled well forward and the sternum elevated so that it lies at the same height as the spine. (b) The X-ray beam is centred at the caudal aspect of the scapula. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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5.3

Patient positioning for a DV view of the thorax. The thorax should be straight with the sternum and spine superimposed. In deep-chested animals, a radiolucent plastic or foam trough can be used to stabilize the animal and avoid rotation. The X-ray beam should be centred to the caudal aspect of the scapula. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2013 British Small Animal Veterinary Association

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5.3 Patient positioning for a DV view of the thorax. The thorax should be straight with the sternum and spine superimposed. In deep-chested animals, a radiolucent plastic or foam trough can be used to stabilize the animal and avoid rotation. The X-ray beam should be centred to the caudal aspect of the scapula. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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5.4

Patient positioning for a VD view of the thorax. The thorax should be straight with the sternum and spine superimposed. In deep-chested animals, a radiolucent plastic or foam trough can be used to stabilize the animal and avoid rotation. The X-ray beam is centred on the mid-sternum. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2013 British Small Animal Veterinary Association

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5.4 Patient positioning for a VD view of the thorax. The thorax should be straight with the sternum and spine superimposed. In deep-chested animals, a radiolucent plastic or foam trough can be used to stabilize the animal and avoid rotation. The X-ray beam is centred on the mid-sternum. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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5.5

Patient positioning for a left lateral decubitus view of the thorax. When using a horizontal beam, radiation safety requires that the barrier at which the beam is directed is at least double brick thickness or lead lined to a thickness of 2 mm. The patient is positioned in lateral recumbency and the X-ray beam is collimated to the plate. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2013 British Small Animal Veterinary Association

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5.5 Patient positioning for a left lateral decubitus view of the thorax. When using a horizontal beam, radiation safety requires that the barrier at which the beam is directed is at least double brick thickness or lead lined to a thickness of 2 mm. The patient is positioned in lateral recumbency and the X-ray beam is collimated to the plate. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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5.6

(a) Patient positioning for a horizontal beam lateral standing view of the thorax. The cassette (arrowed) is positioned vertically. Superimposition of the forelimbs and elbows over the cranioventral thorax will be greater than for the equivalent recumbent lateral view. (b) Recumbent lateral view of the thorax of a cat with an irregularly marginated, soft tissue opacity superimposed on the caudodorsal thorax (arrowed). (c) The horizontal beam lateral radiograph demonstrates that this soft tissue opacity has moved and therefore represents fluid rather than a mass lesion. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2013 British Small Animal Veterinary Association

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5.6 (a) Patient positioning for a horizontal beam lateral standing view of the thorax. The cassette (arrowed) is positioned vertically. Superimposition of the forelimbs and elbows over the cranioventral thorax will be greater than for the equivalent recumbent lateral view. (b) Recumbent lateral view of the thorax of a cat with an irregularly marginated, soft tissue opacity superimposed on the caudodorsal thorax (arrowed). (c) The horizontal beam lateral radiograph demonstrates that this soft tissue opacity has moved and therefore represents fluid rather than a mass lesion. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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5.7

Patient positioning for an oblique DV view of the thorax. In most cases, this view is obtained in animals with a palpable thoracic wall mass. The thorax of the animal is rotated until the ‘shadow’ of the mass created by the light beam diaphragm is maximized. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2013 British Small Animal Veterinary Association

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5.7 Patient positioning for an oblique DV view of the thorax. In most cases, this view is obtained in animals with a palpable thoracic wall mass. The thorax of the animal is rotated until the ‘shadow’ of the mass created by the light beam diaphragm is maximized. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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5.8

Patient positioning for a tangential craniocaudal view of the thoracic inlet. This view is very difficult to achieve without restraint by sedation or general anaesthesia, and has largely been superseded by endoscopy and CT. The endotracheal tube must be removed before the exposure is taken. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2013 British Small Animal Veterinary Association

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5.8 Patient positioning for a tangential craniocaudal view of the thoracic inlet. This view is very difficult to achieve without restraint by sedation or general anaesthesia, and has largely been superseded by endoscopy and CT. The endotracheal tube must be removed before the exposure is taken. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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5.9

DV view of the thorax of a cat. The narrow cranial mediastinum (arrowed) should not exceed the width of the spine. Compare this with the dog in Figure 5.11 in which the normal mediastinum should not exceed twice the width of the spine. © 2013 British Small Animal Veterinary Association

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5.9 DV view of the thorax of a cat. The narrow cranial mediastinum (arrowed) should not exceed the width of the spine. Compare this with the dog in Figure 5.11 in which the normal mediastinum should not exceed twice the width of the spine.

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5.10

Right lateral view of the thorax of a cat. The small wedge of soft tissue between the spine and the tip of the caudodorsal lung (arrowed) is normal in the cat and is due to the increased visibility of the psoas minor muscle. © 2013 British Small Animal Veterinary Association

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5.10 Right lateral view of the thorax of a cat. The small wedge of soft tissue between the spine and the tip of the caudodorsal lung (arrowed) is normal in the cat and is due to the increased visibility of the psoas minor muscle.

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5.11

DV view of the thorax of a normal Springer Spaniel. A = caudal lobe pulmonary artery; Ac = cardiac apex; B = right and left caudal lobe bronchi; C = carina; CM = caudal mediastinal reflection; CVC = caudal vena cava; S = stomach; T = trachea; V = caudal lobe pulmonary vein; black arrows = cranioventral mediastinal reflection; dashed white arrows = lingula of the left cranial lung lobe; solid arrow = width of the craniodorsal mediastinum. © 2013 British Small Animal Veterinary Association

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5.11 DV view of the thorax of a normal Springer Spaniel. A = caudal lobe pulmonary artery; Ac = cardiac apex; B = right and left caudal lobe bronchi; C = carina; CM = caudal mediastinal reflection; CVC = caudal vena cava; S = stomach; T = trachea; V = caudal lobe pulmonary vein; black arrows = cranioventral mediastinal reflection; dashed white arrows = lingula of the left cranial lung lobe; solid arrow = width of the craniodorsal mediastinum.

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5.12

Left lateral view of the thorax of a normal English Springer Spaniel. A = cranial lobe pulmonary artery; Ao = descending aorta; C = carina; CVC = caudal vena cava; LC = left crus of the diaphragm; PA = caudal lobar pulmonary arteries and veins (superimposed); RC = right crus of the diaphragm; T = trachea; V = cranial lobe pulmonary vein. © 2013 British Small Animal Veterinary Association

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5.12 Left lateral view of the thorax of a normal English Springer Spaniel. A = cranial lobe pulmonary artery; Ao = descending aorta; C = carina; CVC = caudal vena cava; LC = left crus of the diaphragm; PA = caudal lobar pulmonary arteries and veins (superimposed); RC = right crus of the diaphragm; T = trachea; V = cranial lobe pulmonary vein.

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5.13

Right lateral view of the thorax of a normal English Springer Spaniel. A = cranial lobe pulmonary artery; Ao = descending aorta; C = carina; CVC = caudal vena cava; LC = left crus of the diaphragm; PA = caudal lobar pulmonary arteries and veins (superimposed); RC = right crus of the diaphragm; S = stomach; T = trachea; V = cranial lobe pulmonary vein; dashed arrow = lingula of the left cranial lung lobe; solid arrow = approximate height of the craniodorsal mediastinum. © 2013 British Small Animal Veterinary Association

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5.13 Right lateral view of the thorax of a normal English Springer Spaniel. A = cranial lobe pulmonary artery; Ao = descending aorta; C = carina; CVC = caudal vena cava; LC = left crus of the diaphragm; PA = caudal lobar pulmonary arteries and veins (superimposed); RC = right crus of the diaphragm; S = stomach; T = trachea; V = cranial lobe pulmonary vein; dashed arrow = lingula of the left cranial lung lobe; solid arrow = approximate height of the craniodorsal mediastinum.

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5.14

(a) Right lateral and (b) DV views of the thorax of a Bassett Hound. The thorax is broad and dorsoventrally flattened. On the lateral view this results in a lucent appearance to the mid-thoracic vertebral bodies (arrowed) which should not be mistaken for osteopenia. On the DV view the prominent costochondral junctions and skin folds should not be mistaken for retraction of the lung lobes and pleural effusion (arrowed). In this dog, the artefact is only recognized on the right side of the thorax because of axial rotation of the thorax. © 2013 British Small Animal Veterinary Association

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5.14 (a) Right lateral and (b) DV views of the thorax of a Bassett Hound. The thorax is broad and dorsoventrally flattened. On the lateral view this results in a lucent appearance to the mid-thoracic vertebral bodies (arrowed) which should not be mistaken for osteopenia. On the DV view the prominent costochondral junctions and skin folds should not be mistaken for retraction of the lung lobes and pleural effusion (arrowed). In this dog, the artefact is only recognized on the right side of the thorax because of axial rotation of the thorax.

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5.15

DV view of the thorax of a deep-chested dog. The skin folds (arrowed) are prominent and the lucent area (*) lateral to these lines should not be mistaken for pneumothorax. The distinction can be made by tracing the line of the skin fold beyond the thoracic wall, by recognizing that the change is symmetrical and that, using a bright light/adjusting contrast and brightness, vascular markings can be seen to extend to the periphery of the thorax. © 2013 British Small Animal Veterinary Association

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5.15 DV view of the thorax of a deep-chested dog. The skin folds (arrowed) are prominent and the lucent area (*) lateral to these lines should not be mistaken for pneumothorax. The distinction can be made by tracing the line of the skin fold beyond the thoracic wall, by recognizing that the change is symmetrical and that, using a bright light/adjusting contrast and brightness, vascular markings can be seen to extend to the periphery of the thorax.

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5.16

(a) Lateral and (b) DV views of the thorax of a clinically normal elderly dog. Note the increased visibility of the bronchial walls. This is a non-specific radiological finding in older animals. Changes due to chronic lower airway disease can appear similar. © 2013 British Small Animal Veterinary Association

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5.16 (a) Lateral and (b) DV views of the thorax of a clinically normal elderly dog. Note the increased visibility of the bronchial walls. This is a non-specific radiological finding in older animals. Changes due to chronic lower airway disease can appear similar.

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5.17

Location of lung lobes and fissures. Since only fluid-filled fissures that are tangential to the X-ray beam are visible, the volume of fluid and the position of the patient will determine the fissures that are seen. (a) Fissures of the lateral aspect of the left lung (looking right to left) are more likely to be seen when the patient is in left recumbency. (b) Fissures of the lateral aspect of the right lung (looking medial to lateral) are more likely to be seen when the patient is in right recumbency. (c) Fissures on the dorsal aspect of the lungs are more likely to be seen when the patient is in dorsal recumbency. (d) Fissures on the ventral aspect of the lungs are more likely to be seen when the patient is in ventral recumbency. A = accessory lobe; CdCr = caudal part of the left cranial lobe; Cr = right cranial lobe; CrCr = cranial part of the left cranial lobe; Cs = costodiaphragmatic recess; F = interlobar fissure; LCd = left caudal lobe; M = mediastinal reflection; Md = right middle lobe; RCd = right caudal lobe; V = caudoventral mediastinal reflection between the left caudal lobe and the accessory lobe (pleural fluid may accumulate adjacent to this reflection). Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2013 British Small Animal Veterinary Association

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5.17 Location of lung lobes and fissures. Since only fluid-filled fissures that are tangential to the X-ray beam are visible, the volume of fluid and the position of the patient will determine the fissures that are seen. (a) Fissures of the lateral aspect of the left lung (looking right to left) are more likely to be seen when the patient is in left recumbency. (b) Fissures of the lateral aspect of the right lung (looking medial to lateral) are more likely to be seen when the patient is in right recumbency. (c) Fissures on the dorsal aspect of the lungs are more likely to be seen when the patient is in dorsal recumbency. (d) Fissures on the ventral aspect of the lungs are more likely to be seen when the patient is in ventral recumbency. A = accessory lobe; CdCr = caudal part of the left cranial lobe; Cr = right cranial lobe; CrCr = cranial part of the left cranial lobe; Cs = costodiaphragmatic recess; F = interlobar fissure; LCd = left caudal lobe; M = mediastinal reflection; Md = right middle lobe; RCd = right caudal lobe; V = caudoventral mediastinal reflection between the left caudal lobe and the accessory lobe (pleural fluid may accumulate adjacent to this reflection). Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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5.18

Lateral view of the thorax of a dog during (a) expiration and (b) inspiration. (a) During expiration the caudodorsal lung (*) is increased in opacity, which may be mistaken for a pathological infiltrate. The volume of the thorax is reduced with overlap of the cardiac silhouette and diaphragm (black arrow). Kinking of the terminal trachea (white arrow) should not be mistaken for a mass lesion at the heart base. (b) Following manual inflation. The lungs, although not maximally inflated, have a normal bronchovascular pattern (arrowed). © 2013 British Small Animal Veterinary Association

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5.18 Lateral view of the thorax of a dog during (a) expiration and (b) inspiration. (a) During expiration the caudodorsal lung (*) is increased in opacity, which may be mistaken for a pathological infiltrate. The volume of the thorax is reduced with overlap of the cardiac silhouette and diaphragm (black arrow). Kinking of the terminal trachea (white arrow) should not be mistaken for a mass lesion at the heart base. (b) Following manual inflation. The lungs, although not maximally inflated, have a normal bronchovascular pattern (arrowed).

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5.19

Lateral view of the thorax of a dog with pulmonary osteomas. These multiple scattered mineral opacities (arrowheads) are of no clinical significance. They appear more radiopaque than soft tissue nodules (e.g. metastases) of a similar size and are usually more irregular in shape. © 2013 British Small Animal Veterinary Association

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5.19 Lateral view of the thorax of a dog with pulmonary osteomas. These multiple scattered mineral opacities (arrowheads) are of no clinical significance. They appear more radiopaque than soft tissue nodules (e.g. metastases) of a similar size and are usually more irregular in shape.

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5.20

(a) Lateral view of the thorax of an obese dog. The cardiac silhouette is elevated by fat (arrowheads). Fat clearly outlines the cardiac silhouette, whereas pleural fluid or a ventrally located mass obscures it. When measuring the cardiac silhouette, any surrounding fat should not be included in the measurements. (b) DV view of the thorax of an obese cat. A large quantity of fat is present within the subcutis (*). Within the thorax, the cranial mediastinum is widened (arrowed) and fat is present within and adjacent to the pericardium (arrowhead). Fat surrounding the thorax will increase the overall opacity of the image, as well as increase scatter. The quality of the radiograph is degraded. In extreme cases, fat may also physically limit inspiratory movement. © 2013 British Small Animal Veterinary Association

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5.20 (a) Lateral view of the thorax of an obese dog. The cardiac silhouette is elevated by fat (arrowheads). Fat clearly outlines the cardiac silhouette, whereas pleural fluid or a ventrally located mass obscures it. When measuring the cardiac silhouette, any surrounding fat should not be included in the measurements. (b) DV view of the thorax of an obese cat. A large quantity of fat is present within the subcutis (*). Within the thorax, the cranial mediastinum is widened (arrowed) and fat is present within and adjacent to the pericardium (arrowhead). Fat surrounding the thorax will increase the overall opacity of the image, as well as increase scatter. The quality of the radiograph is degraded. In extreme cases, fat may also physically limit inspiratory movement.

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5.21

Location of the cardiac chambers in a dog. (a) Lateral view. (b) Ventral view. Note that on the ventral view, the ascending aorta, brachiocephalic trunk and left subclavian artery lie on the midline. The main pulmonary artery and left auricular appendage margins are superimposed on the centre of the cardiac silhouette. They are only visible individually when markedly enlarged and alter the margin of the cardiac silhouette. The left atrium (not shown) is superimposed on the centre of the cardiac silhouette (between the mainstem bronchi). Ao = aortic arch; BR = brachiocephalic trunk; CdVC = caudal vena cava; CrVC = cranial vena cava; IT = internal thoracic arteries and veins; LA = left atrium; LAu = left auricular appendage; LPA = left pulmonary artery; LS = left subclavian artery; LV = left ventricle; MPA = main pulmonary artery; RA = right atrium; RAu = right auricular appendage; RPA = right pulmonary artery; RV = right ventricle. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2013 British Small Animal Veterinary Association

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5.21 Location of the cardiac chambers in a dog. (a) Lateral view. (b) Ventral view. Note that on the ventral view, the ascending aorta, brachiocephalic trunk and left subclavian artery lie on the midline. The main pulmonary artery and left auricular appendage margins are superimposed on the centre of the cardiac silhouette. They are only visible individually when markedly enlarged and alter the margin of the cardiac silhouette. The left atrium (not shown) is superimposed on the centre of the cardiac silhouette (between the mainstem bronchi). Ao = aortic arch; BR = brachiocephalic trunk; CdVC = caudal vena cava; CrVC = cranial vena cava; IT = internal thoracic arteries and veins; LA = left atrium; LAu = left auricular appendage; LPA = left pulmonary artery; LS = left subclavian artery; LV = left ventricle; MPA = main pulmonary artery; RA = right atrium; RAu = right auricular appendage; RPA = right pulmonary artery; RV = right ventricle. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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5.22

Location of the cardiac chambers in a cat. (a) Lateral view. (b) Ventral view. Note that on the ventral view, the main pulmonary artery and left auricular appendage margins are superimposed on the cardiac silhouette. They are only visible individually when markedly enlarged and alter the margin of the cardiac silhouette. The left atrium (not shown) is superimposed on the centre of the cardiac silhouette (between the mainstem bronchi). Ao = aortic arch; CdVC = caudal vena cava; CrVC = cranial vena cava; LAu = left auricular appendage; LV = left ventricle; MPA = main pulmonary artery; RA = right atrium; RAu = right auricular appendage; RV = right ventricle. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2013 British Small Animal Veterinary Association

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5.22 Location of the cardiac chambers in a cat. (a) Lateral view. (b) Ventral view. Note that on the ventral view, the main pulmonary artery and left auricular appendage margins are superimposed on the cardiac silhouette. They are only visible individually when markedly enlarged and alter the margin of the cardiac silhouette. The left atrium (not shown) is superimposed on the centre of the cardiac silhouette (between the mainstem bronchi). Ao = aortic arch; CdVC = caudal vena cava; CrVC = cranial vena cava; LAu = left auricular appendage; LV = left ventricle; MPA = main pulmonary artery; RA = right atrium; RAu = right auricular appendage; RV = right ventricle. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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5.23

Location of the cardiac chambers using the ‘clock face’ analogy. (a) Lateral view. (b) DV view. A = aorta; LA = left atrium; LAu = left auricular appendage; LV = left ventricle; MPA = main pulmonary artery; RA = right atrium; RAu = right auricular appendage; RV = right ventricle. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2013 British Small Animal Veterinary Association

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5.23 Location of the cardiac chambers using the ‘clock face’ analogy. (a) Lateral view. (b) DV view. A = aorta; LA = left atrium; LAu = left auricular appendage; LV = left ventricle; MPA = main pulmonary artery; RA = right atrium; RAu = right auricular appendage; RV = right ventricle. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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5.25

VD view of the thorax of a dog. The shape of the diaphragm differs compared with a DV view. Three ‘domes’ are created by the two crura (dashed arrows and lines) and the cupola (solid arrow) of the diaphragm. © 2013 British Small Animal Veterinary Association

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5.25 VD view of the thorax of a dog. The shape of the diaphragm differs compared with a DV view. Three ‘domes’ are created by the two crura (dashed arrows and lines) and the cupola (solid arrow) of the diaphragm.

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5.26

DV view of the thorax showing the position of the cranial, middle and caudal parts of the mediastinum, including the position of the thymus. A = accessory lobe of the right lung (seen as a dotted area); CdVC = caudal vena cava; Cm = cranial mediastinum; CrVC = cranial vena cava; CVM = caudoventral mediastinal reflection; Mr = mediastinal recess, which accommodates the accessory lobe of the right lung; RCr = right cranial lung lobe (seen as a dotted area); Th = position of the vestigial thymus. (Adapted from Suter (1984) with permission) © 2013 British Small Animal Veterinary Association

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5.26 DV view of the thorax showing the position of the cranial, middle and caudal parts of the mediastinum, including the position of the thymus. A = accessory lobe of the right lung (seen as a dotted area); CdVC = caudal vena cava; Cm = cranial mediastinum; CrVC = cranial vena cava; CVM = caudoventral mediastinal reflection; Mr = mediastinal recess, which accommodates the accessory lobe of the right lung; RCr = right cranial lung lobe (seen as a dotted area); Th = position of the vestigial thymus. (Adapted from Suter (1984) with permission)

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5.27

Transverse view of the cranial mediastinum at the level of the second thoracic vertebra. B = brachiocephalic artery; CA = right and left carotid arteries; Cm = cranial mediastinum; CrVC = cranial vena cava; DCV = right deep cranial vertebral vein and left deep cranial vertebral vein; Ls = left subclavian artery; M = longus colli muscle; O = oesophagus; T = trachea; VV = right and left vertebral veins. (Adapted from Suter (1984) with permission) © 2013 British Small Animal Veterinary Association

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5.27 Transverse view of the cranial mediastinum at the level of the second thoracic vertebra. B = brachiocephalic artery; CA = right and left carotid arteries; Cm = cranial mediastinum; CrVC = cranial vena cava; DCV = right deep cranial vertebral vein and left deep cranial vertebral vein; Ls = left subclavian artery; M = longus colli muscle; O = oesophagus; T = trachea; VV = right and left vertebral veins. (Adapted from Suter (1984) with permission)

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5.28

Lateral view of the thorax of a cat. The normal thymus is of soft tissue opacity and is approximately triangular in shape (arrowed). Caudally, it may efface the cranial border of the cardiac silhouette. © 2013 British Small Animal Veterinary Association

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5.28 Lateral view of the thorax of a cat. The normal thymus is of soft tissue opacity and is approximately triangular in shape (arrowed). Caudally, it may efface the cranial border of the cardiac silhouette.

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5.29

(a) Lateral and (b) DV views of the thorax illustrating the five main locations of mediastinal masses. A = descending thoracic aorta; C = caudal vena cava; F = fat in ventral mediastinum; M = shadow of intrathoracic part of the longus colli muscle; O = oesophagus; T = trachea; V = cranioventral masses; W = craniodorsal masses; X = hilar and perihilar masses; Y = caudodorsal masses; Z = caudoventral masses. (Reproduced from Suter (1984) with permission) © 2013 British Small Animal Veterinary Association

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5.29 (a) Lateral and (b) DV views of the thorax illustrating the five main locations of mediastinal masses. A = descending thoracic aorta; C = caudal vena cava; F = fat in ventral mediastinum; M = shadow of intrathoracic part of the longus colli muscle; O = oesophagus; T = trachea; V = cranioventral masses; W = craniodorsal masses; X = hilar and perihilar masses; Y = caudodorsal masses; Z = caudoventral masses. (Reproduced from Suter (1984) with permission)

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5.30

(a) Lateral and (b) DV views of the thorax of a dog with a craniodorsal mediastinal mass. (a) The large soft tissue mass ventral to T1–T6 results in ventral displacement (arrowed) of the intrathoracic trachea. The displaced cranial lung lobes are poorly inflated and extend only to the second rib. (b) On the DV view, the mass (arrowed) results in widening of the cranial mediastinum but does not cause significant lateral displacement of the trachea (T). © 2013 British Small Animal Veterinary Association

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5.30 (a) Lateral and (b) DV views of the thorax of a dog with a craniodorsal mediastinal mass. (a) The large soft tissue mass ventral to T1–T6 results in ventral displacement (arrowed) of the intrathoracic trachea. The displaced cranial lung lobes are poorly inflated and extend only to the second rib. (b) On the DV view, the mass (arrowed) results in widening of the cranial mediastinum but does not cause significant lateral displacement of the trachea (T).

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5.31

(a) Lateral view of the thorax of a dog with a large caudodorsal mediastinal mass. The mass (arrowed) is superimposed on the caudodorsal lung fields and dorsal two-thirds of the diaphragm. The mass obscures the caudal vena cava. (b) DV view of the thorax of a dog with a large caudodorsal mediastinal mass. The mass (arrowed) is localized to the midline. The differential diagnoses include a neoplastic mass, granuloma or abscess arising from the mediastinum itself, or a mass lesion involving the caudal oesophagus. © 2013 British Small Animal Veterinary Association

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5.31 (a) Lateral view of the thorax of a dog with a large caudodorsal mediastinal mass. The mass (arrowed) is superimposed on the caudodorsal lung fields and dorsal two-thirds of the diaphragm. The mass obscures the caudal vena cava. (b) DV view of the thorax of a dog with a large caudodorsal mediastinal mass. The mass (arrowed) is localized to the midline. The differential diagnoses include a neoplastic mass, granuloma or abscess arising from the mediastinum itself, or a mass lesion involving the caudal oesophagus.

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5.32

(a) Lateral and (b) DV views of the thorax of a dog with a caudoventral mediastinal mass. (a) The mass (white arrows) effaces the caudoventral border of the cardiac silhouette and the cranioventral diaphragm. Pleural effusion is present with widening of the pleural fissures (black arrow). (b) The location of the mass (white arrows) is partially obscured by pleural fluid. Note the widened pleural fissures (black arrows). As the volume of pleural fluid is not large, the mass is suspected to arise on the midline and extend slightly to the left. Differential diagnoses include a caudoventral mediastinal mass, accessory lung lobe mass or a diaphragmatic defect. © 2013 British Small Animal Veterinary Association

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5.32 (a) Lateral and (b) DV views of the thorax of a dog with a caudoventral mediastinal mass. (a) The mass (white arrows) effaces the caudoventral border of the cardiac silhouette and the cranioventral diaphragm. Pleural effusion is present with widening of the pleural fissures (black arrow). (b) The location of the mass (white arrows) is partially obscured by pleural fluid. Note the widened pleural fissures (black arrows). As the volume of pleural fluid is not large, the mass is suspected to arise on the midline and extend slightly to the left. Differential diagnoses include a caudoventral mediastinal mass, accessory lung lobe mass or a diaphragmatic defect.

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5.33

Basic principles of tracheal and bronchial displacement on the lateral thoracic radiograph. The position of the trachea and the mainstem bronchi can be used to assess for the presence of cardiac disease and mediastinal masses. (a) Normal. In most breeds, the trachea diverges gradually from the thoracic spine towards the base of the cardiac silhouette. In some breeds with a shallow conformation there may be no divergence, and in some deep-chested breeds the intrathoracic trachea may diverge even when significant cardiac enlargement is present. The distal trachea curves slightly ventrally cranial to the carina (arrowed). (b) Enlargement of the left ventricle results in elevation of the trachea along its length. The trachea no longer diverges but is almost parallel to the thoracic spine. (c) Enlargement of the left atrium results in dorsal displacement of the left mainstem bronchus (shown in dark blue). (d) Cranial mediastinal masses result in elevation of the trachea cranial to the cardiac silhouette. Depending on the size and location of the mass, the dorsal displacement may be focal or along the length of the trachea. Very large masses may compress and narrow the lumen of the trachea. (e) Heart base masses result in focal elevation of the trachea immediately cranial to the carina. This has been termed the ‘bowler hat’ sign. The terminal trachea is displaced to the right on the DV view. Note that the position of the terminal trachea is usually not altered on the lateral view in animals with tracheobronchial lymphadenopathy. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission. © 2013 British Small Animal Veterinary Association

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5.33 Basic principles of tracheal and bronchial displacement on the lateral thoracic radiograph. The position of the trachea and the mainstem bronchi can be used to assess for the presence of cardiac disease and mediastinal masses. (a) Normal. In most breeds, the trachea diverges gradually from the thoracic spine towards the base of the cardiac silhouette. In some breeds with a shallow conformation there may be no divergence, and in some deep-chested breeds the intrathoracic trachea may diverge even when significant cardiac enlargement is present. The distal trachea curves slightly ventrally cranial to the carina (arrowed). (b) Enlargement of the left ventricle results in elevation of the trachea along its length. The trachea no longer diverges but is almost parallel to the thoracic spine. (c) Enlargement of the left atrium results in dorsal displacement of the left mainstem bronchus (shown in dark blue). (d) Cranial mediastinal masses result in elevation of the trachea cranial to the cardiac silhouette. Depending on the size and location of the mass, the dorsal displacement may be focal or along the length of the trachea. Very large masses may compress and narrow the lumen of the trachea. (e) Heart base masses result in focal elevation of the trachea immediately cranial to the carina. This has been termed the ‘bowler hat’ sign. The terminal trachea is displaced to the right on the DV view. Note that the position of the terminal trachea is usually not altered on the lateral view in animals with tracheobronchial lymphadenopathy. Drawn by S.J. Elmhurst BA Hons (www.livingart.org.uk) and reproduced with her permission.

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5.34

Lateral fluoroscopic images of the cervical trachea of a dog with tracheal collapse. On fluoroscopic images, the normal radiographic opacities are reversed (i.e. air appears white). (a) During expiration the tracheal diameter (arrowheads) is even throughout its length. (b) During inspiration, the air-filled lumen collapses (arrowheads). In a normal animal, the tracheal luminal diameter should not change significantly between inspiration and expiration. © 2013 British Small Animal Veterinary Association

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5.34 Lateral fluoroscopic images of the cervical trachea of a dog with tracheal collapse. On fluoroscopic images, the normal radiographic opacities are reversed (i.e. air appears white). (a) During expiration the tracheal diameter (arrowheads) is even throughout its length. (b) During inspiration, the air-filled lumen collapses (arrowheads). In a normal animal, the tracheal luminal diameter should not change significantly between inspiration and expiration.

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5.35

(a) Left lateral and (b) right lateral views of the thorax of a dog with a tracheal foreign body (arrowed) that has lodged in the left cranial lobar bronchus. (a) The foreign body (a canine tooth) is visible superimposed on the distal trachea. The margins are poorly defined due to atelectasis of the left cranial lobe. (b) The affected lobe is uppermost and well inflated and the tooth is surrounded by air making it clearly visible. (c) DV view of the thorax of a dog with a tracheal foreign body (arrowed) that has lodged in the left cranial lobar bronchus. The tooth is difficult to recognize as it is superimposed on the cardiac silhouette. This study demonstrates the importance of obtaining both lateral views and an orthogonal view, as well as the selection of appropriate exposure factors, which allow the lesion to be localized on the DV view. Underexposure of the DV view would probably have prevented the tooth from being recognized. (Courtesy of the University of Cambridge) © 2013 British Small Animal Veterinary Association

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5.35 (a) Left lateral and (b) right lateral views of the thorax of a dog with a tracheal foreign body (arrowed) that has lodged in the left cranial lobar bronchus. (a) The foreign body (a canine tooth) is visible superimposed on the distal trachea. The margins are poorly defined due to atelectasis of the left cranial lobe. (b) The affected lobe is uppermost and well inflated and the tooth is surrounded by air making it clearly visible. (c) DV view of the thorax of a dog with a tracheal foreign body (arrowed) that has lodged in the left cranial lobar bronchus. The tooth is difficult to recognize as it is superimposed on the cardiac silhouette. This study demonstrates the importance of obtaining both lateral views and an orthogonal view, as well as the selection of appropriate exposure factors, which allow the lesion to be localized on the DV view. Underexposure of the DV view would probably have prevented the tooth from being recognized. (Courtesy of the University of Cambridge)

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5.36

Lateral view of the thorax of a Bulldog with hypoplasia of the trachea. The ratio of the tracheal luminal diameter to the thoracic inlet is 0.09 (normal range for non-brachycephalic breeds is 0.21 ± 0.03 and for Bulldogs is 0.11 ± 0.03). The trachea is uniformly narrowed along its length. © 2013 British Small Animal Veterinary Association

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5.36 Lateral view of the thorax of a Bulldog with hypoplasia of the trachea. The ratio of the tracheal luminal diameter to the thoracic inlet is 0.09 (normal range for non-brachycephalic breeds is 0.21 ± 0.03 and for Bulldogs is 0.11 ± 0.03). The trachea is uniformly narrowed along its length.

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5.37

(a) Left and (b) right lateral views of the thorax of a cat with focal narrowing of the trachea (arrowed). The trachea should be of even diameter along its length. The narrowing is consistent on both views and was confirmed using endoscopy. Narrowing may be acquired following trauma associated with overinflation of the endotracheal tube cuff, foreign body trauma or inflammation. © 2013 British Small Animal Veterinary Association

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5.37 (a) Left and (b) right lateral views of the thorax of a cat with focal narrowing of the trachea (arrowed). The trachea should be of even diameter along its length. The narrowing is consistent on both views and was confirmed using endoscopy. Narrowing may be acquired following trauma associated with overinflation of the endotracheal tube cuff, foreign body trauma or inflammation.

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5.38

(a) Lateral and (b) DV views of the thorax of a cat with a tracheal mass at the level of the carina. (a) There is an increase in soft tissue opacity within the terminal trachea (arrowhead). The left cranial lobe bronchus is obstructed, resulting in a reduction in lung volume, and the right lung lobes consequently show compensatory overinflation (double-headed arrow). (b) The caudal sub-segment of the left cranial lung lobe is collapsed (*), resulting in a mediastinal shift to the same side (arrowheads). The trachea itself is not clearly seen as it is largely superimposed on the spine. © 2013 British Small Animal Veterinary Association

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5.38 (a) Lateral and (b) DV views of the thorax of a cat with a tracheal mass at the level of the carina. (a) There is an increase in soft tissue opacity within the terminal trachea (arrowhead). The left cranial lobe bronchus is obstructed, resulting in a reduction in lung volume, and the right lung lobes consequently show compensatory overinflation (double-headed arrow). (b) The caudal sub-segment of the left cranial lung lobe is collapsed (*), resulting in a mediastinal shift to the same side (arrowheads). The trachea itself is not clearly seen as it is largely superimposed on the spine.

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5.39

(a) Lateral and (b) DV views of the thorax of a dog with extensive luminal narrowing of the trachea due to submucosal haemorrhage. (a) The band-like thickening (arrowed) is most severe within the thoracic inlet, with sparing of the terminal trachea. (b) The trachea lies in a normal position. A pleural line (arrowed) is present in the right fourth to fifth intercostal spaces, which could represent pleural thickening/fluid or may be incidental. © 2013 British Small Animal Veterinary Association

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5.39 (a) Lateral and (b) DV views of the thorax of a dog with extensive luminal narrowing of the trachea due to submucosal haemorrhage. (a) The band-like thickening (arrowed) is most severe within the thoracic inlet, with sparing of the terminal trachea. (b) The trachea lies in a normal position. A pleural line (arrowed) is present in the right fourth to fifth intercostal spaces, which could represent pleural thickening/fluid or may be incidental.

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5.40

(a) Right lateral and (b) DV views of the thorax of a dog with an alveolar lung pattern (as a result of pulmonary oedema secondary to congestive cardiac failure). Note the tall heart and fluffy increase in opacity in the perihilar area, which obscures the caudodorsal margin of the cardiac silhouette (white arrows). Thickening of the bronchial wall is due to peribronchial oedema (black arrow). (c) Lateral and (d) DV radiographs of the same dog as in (a) and (b) following diuresis. The oedema has resolved and the cardiac outline is now clearly visible. © 2013 British Small Animal Veterinary Association

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5.40 (a) Right lateral and (b) DV views of the thorax of a dog with an alveolar lung pattern (as a result of pulmonary oedema secondary to congestive cardiac failure). Note the tall heart and fluffy increase in opacity in the perihilar area, which obscures the caudodorsal margin of the cardiac silhouette (white arrows). Thickening of the bronchial wall is due to peribronchial oedema (black arrow). (c) Lateral and (d) DV radiographs of the same dog as in (a) and (b) following diuresis. The oedema has resolved and the cardiac outline is now clearly visible.

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5.41

(a) Left lateral and (b) DV views of the thorax of a dog with an alveolar lung pattern (as a result of pulmonary oedema due to left-sided congestive heart failure). The widespread alveolar infiltrate is ‘fluffy’ and less confluent cranially and dorsally, but becomes more intense (consolidated) in the perihilar and caudodorsal lung regions (arrowed). Occasional air bronchograms are present. Factors that must be considered to confirm that the radiographic changes are due to cardiogenic pulmonary oedema include distribution of the changes, size of the cardiac chambers and pulmonary venous enlargement, as well as breed and clinical findings. In this dog, the lobar veins are difficult to assess due to the severity of the pulmonary changes, the left atrium is obscured on the lateral view and, as it is a deep-chested dog, assessment of cardiac size is more difficult. Hence, clinical findings and response to treatment are important considerations. © 2013 British Small Animal Veterinary Association

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5.41 (a) Left lateral and (b) DV views of the thorax of a dog with an alveolar lung pattern (as a result of pulmonary oedema due to left-sided congestive heart failure). The widespread alveolar infiltrate is ‘fluffy’ and less confluent cranially and dorsally, but becomes more intense (consolidated) in the perihilar and caudodorsal lung regions (arrowed). Occasional air bronchograms are present. Factors that must be considered to confirm that the radiographic changes are due to cardiogenic pulmonary oedema include distribution of the changes, size of the cardiac chambers and pulmonary venous enlargement, as well as breed and clinical findings. In this dog, the lobar veins are difficult to assess due to the severity of the pulmonary changes, the left atrium is obscured on the lateral view and, as it is a deep-chested dog, assessment of cardiac size is more difficult. Hence, clinical findings and response to treatment are important considerations.

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5.42

(a) Right lateral and (b) DV views of the thorax of an obese dog with an alveolar lung pattern (due to aspiration pneumonia). (a) Note the severe (but incomplete) consolidation of the cranioventral lung lobes, extending to the periphery of the lobes (white arrows). The margins of the consolidated lung lobes can be identified because of the large deposits of subpleural fat. Multiple air bronchograms (*) as well as peribronchial thickening (black arrow) are visible. (b) The lobar consolidation is bilateral, but appears worse on the left side (solid white arrow) compared with the right side (black arrow). Note the conspicuous lobar sign between the consolidated left lung lobes and the normally inflated accessory lobe of the right lung (dashed white arrows). © 2013 British Small Animal Veterinary Association

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5.42 (a) Right lateral and (b) DV views of the thorax of an obese dog with an alveolar lung pattern (due to aspiration pneumonia). (a) Note the severe (but incomplete) consolidation of the cranioventral lung lobes, extending to the periphery of the lobes (white arrows). The margins of the consolidated lung lobes can be identified because of the large deposits of subpleural fat. Multiple air bronchograms (*) as well as peribronchial thickening (black arrow) are visible. (b) The lobar consolidation is bilateral, but appears worse on the left side (solid white arrow) compared with the right side (black arrow). Note the conspicuous lobar sign between the consolidated left lung lobes and the normally inflated accessory lobe of the right lung (dashed white arrows).

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5.43

(a) Right lateral and (b) DV views of the thorax of a dog with an alveolar pattern (due to lung contusion/haemorrhage secondary to trauma). (a) Pneumomediastinum (*) is present, allowing the external margins of the aorta (Ao), caudal oesophagus (O) and longus colli muscles (Lc) to be seen. A poorly circumscribed focal area of consolidation (arrowed) is evident superimposed on the diaphragm between the seventh and eighth ribs. (b) A large area of consolidation (poorly circumscribed) is visible in the right lung adjacent to the cardiac silhouette (dashed arrows), in addition to the smaller focal area in the left caudal thorax (solid arrow) (as seen on the lateral view). Subcutaneous emphysema (*) is present. No rib fractures are visible. Haemorrhage following trauma usually presents as focal or multifocal areas of poorly circumscribed pulmonary consolidation. © 2013 British Small Animal Veterinary Association

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5.43 (a) Right lateral and (b) DV views of the thorax of a dog with an alveolar pattern (due to lung contusion/haemorrhage secondary to trauma). (a) Pneumomediastinum (*) is present, allowing the external margins of the aorta (Ao), caudal oesophagus (O) and longus colli muscles (Lc) to be seen. A poorly circumscribed focal area of consolidation (arrowed) is evident superimposed on the diaphragm between the seventh and eighth ribs. (b) A large area of consolidation (poorly circumscribed) is visible in the right lung adjacent to the cardiac silhouette (dashed arrows), in addition to the smaller focal area in the left caudal thorax (solid arrow) (as seen on the lateral view). Subcutaneous emphysema (*) is present. No rib fractures are visible. Haemorrhage following trauma usually presents as focal or multifocal areas of poorly circumscribed pulmonary consolidation.

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5.44

(a) Right lateral and (b) DV views of the thorax of a dog with an alveolar pattern as a result of neoplastic infiltration due to histiocytic sarcoma. The accessory lung lobe (solid white arrows) and areas of the caudodorsal lung lobes (dashed white arrows) are affected. The caudal aspect of the cardiac silhouette and the ventral aspect of the diaphragm are effaced by the consolidated lung. The middle tracheobronchial lymph node is enlarged and the caudal lobe bronchi are displaced laterally (black arrows). © 2013 British Small Animal Veterinary Association

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5.44 (a) Right lateral and (b) DV views of the thorax of a dog with an alveolar pattern as a result of neoplastic infiltration due to histiocytic sarcoma. The accessory lung lobe (solid white arrows) and areas of the caudodorsal lung lobes (dashed white arrows) are affected. The caudal aspect of the cardiac silhouette and the ventral aspect of the diaphragm are effaced by the consolidated lung. The middle tracheobronchial lymph node is enlarged and the caudal lobe bronchi are displaced laterally (black arrows).

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5.45

(a) Right lateral and (b) DV views of the thorax of a dog with Angiostrongylus vasorum infection. The alveolar infiltrate is located predominantly at the periphery of the lung fields on both views (arrowed). This case shows a typical distribution pattern for Angiostrongylus-related pneumonia, although in other cases a patchier, diffuse or even nodular pattern may be present. © 2013 British Small Animal Veterinary Association

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5.45 (a) Right lateral and (b) DV views of the thorax of a dog with Angiostrongylus vasorum infection. The alveolar infiltrate is located predominantly at the periphery of the lung fields on both views (arrowed). This case shows a typical distribution pattern for Angiostrongylus-related pneumonia, although in other cases a patchier, diffuse or even nodular pattern may be present.

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5.46

Lateral views of the thorax of (a) a dog and (b) a cat with pulmonary metastases. The multiple nodular soft tissue opacities (arrowed) are of variable size and irregular in shape. Many are indistinct. © 2013 British Small Animal Veterinary Association

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5.46 Lateral views of the thorax of (a) a dog and (b) a cat with pulmonary metastases. The multiple nodular soft tissue opacities (arrowed) are of variable size and irregular in shape. Many are indistinct.

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5.47

(a) Right lateral and (b) DV views of the thorax of a dog with a cranial thoracic mass and multiple large ‘cannonball’ metastases. The metastases (arrowheads) are most visible where they overlie the caudal border of the mass and the diaphragm. © 2013 British Small Animal Veterinary Association

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5.47 (a) Right lateral and (b) DV views of the thorax of a dog with a cranial thoracic mass and multiple large ‘cannonball’ metastases. The metastases (arrowheads) are most visible where they overlie the caudal border of the mass and the diaphragm.

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5.48

(a) Left lateral, (b) magnified left lateral and (c) DV views of the thorax of a dog with a diffuse miliary lung infiltrate. There are numerous small (miliary) nodules throughout all the lung lobes. In many cases, individual nodules are difficult to recognize (arrowed) and superimposition of multiple nodules results in large composite shadows which mimic alveolar disease. This pattern is more frequently due to neoplasia (metastatic or lymphosarcoma) but the differential diagnoses include rare forms of pneumonia (fungal, mycobacterial or haematogenous bacterial) and disseminated intravascular coagulation. © 2013 British Small Animal Veterinary Association

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5.48 (a) Left lateral, (b) magnified left lateral and (c) DV views of the thorax of a dog with a diffuse miliary lung infiltrate. There are numerous small (miliary) nodules throughout all the lung lobes. In many cases, individual nodules are difficult to recognize (arrowed) and superimposition of multiple nodules results in large composite shadows which mimic alveolar disease. This pattern is more frequently due to neoplasia (metastatic or lymphosarcoma) but the differential diagnoses include rare forms of pneumonia (fungal, mycobacterial or haematogenous bacterial) and disseminated intravascular coagulation.

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5.49

(a) Right lateral and (b) DV views of the thorax of a dog with Pneumocystis carinii pneumonia. The interstitial pattern appears as a diffuse, hazy increased opacity, which blurs the margins of the normal intrathoracic structures (cardiac silhouette, large lobar vascular structures and lobar bronchi). The DV view is rotated, which limits accurate assessment of the cardiac silhouette. © 2013 British Small Animal Veterinary Association

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5.49 (a) Right lateral and (b) DV views of the thorax of a dog with Pneumocystis carinii pneumonia. The interstitial pattern appears as a diffuse, hazy increased opacity, which blurs the margins of the normal intrathoracic structures (cardiac silhouette, large lobar vascular structures and lobar bronchi). The DV view is rotated, which limits accurate assessment of the cardiac silhouette.

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5.50

Right lateral view of the thorax of a dog with lymphoma. A diffuse, interstitial pulmonary infiltrate is present throughout the lungs. Although a degree of peribronchial thickening is present, the interstitial pattern predominates. There is mild enlargement of the presternal lymph node (arrowed) but the tracheobronchial lymph nodes are not visibly enlarged. © 2013 British Small Animal Veterinary Association

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5.50 Right lateral view of the thorax of a dog with lymphoma. A diffuse, interstitial pulmonary infiltrate is present throughout the lungs. Although a degree of peribronchial thickening is present, the interstitial pattern predominates. There is mild enlargement of the presternal lymph node (arrowed) but the tracheobronchial lymph nodes are not visibly enlarged.

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5.51

(a) Right lateral and (b) DV views of the thorax of a dog with a mixed lung pattern due to aspiration pneumonia. There is extensive consolidation (alveolar pattern) of the left cranial lung lobe with air bronchograms (*) visible. The left border of the cardiac silhouette is effaced by the consolidated left lobe (white arrows). The changes within the left lung lobes caudal to the cardiac silhouette and within the right lung (interstitial pattern) are more patchy, blurring, but not effacing, normal thoracic structures (black arrows). Note the increased thickness of the bronchial walls (bronchial pattern) leading to the area of consolidated lung. © 2013 British Small Animal Veterinary Association

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5.51 (a) Right lateral and (b) DV views of the thorax of a dog with a mixed lung pattern due to aspiration pneumonia. There is extensive consolidation (alveolar pattern) of the left cranial lung lobe with air bronchograms (*) visible. The left border of the cardiac silhouette is effaced by the consolidated left lobe (white arrows). The changes within the left lung lobes caudal to the cardiac silhouette and within the right lung (interstitial pattern) are more patchy, blurring, but not effacing, normal thoracic structures (black arrows). Note the increased thickness of the bronchial walls (bronchial pattern) leading to the area of consolidated lung.

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5.52

(a) Right lateral and (b) DV views of the thorax of a cat with a cavitary mass (arrowheads) in the right caudal lung lobe. The wall of the mass is thick and irregular. Neoplasia (both primary and metastatic) is the most common cause of cavitary lesions. Abscesses and granulomas can occasionally present as cavitary mass lesions. Signalment, clinical findings and diagnostic sampling of the mass are required to confirm the diagnosis. The mass was aspirated under ultrasound guidance and although not conclusive, carcinoma was suspected. © 2013 British Small Animal Veterinary Association

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5.52 (a) Right lateral and (b) DV views of the thorax of a cat with a cavitary mass (arrowheads) in the right caudal lung lobe. The wall of the mass is thick and irregular. Neoplasia (both primary and metastatic) is the most common cause of cavitary lesions. Abscesses and granulomas can occasionally present as cavitary mass lesions. Signalment, clinical findings and diagnostic sampling of the mass are required to confirm the diagnosis. The mass was aspirated under ultrasound guidance and although not conclusive, carcinoma was suspected.

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5.53

(a) DV and (b) lateral views of the thorax of a dog with hyperinflation of the left cranial lung lobe. (a) The left cranial lung lobe (white arrows) is hyperinflated with displacement of the trachea to the right (black arrows). The mediastinal shift is marked such that there is incomplete inflation of the right cranial lung lobe with the tip only reaching the third intercostal space. The hyperinflated lobe lacks lung and vascular markings (*), indicating emphysema. (b) The hyperinflated left cranial lobe (solid white arrows) and the cranial lobar vessels (dashed white arrow) are visible. The emphysematous changes were due to a ‘ball valve’ effect of chronic distortion and inflammation of the left cranial lobe bronchus. O = air-filled oesophagus. © 2013 British Small Animal Veterinary Association

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5.53 (a) DV and (b) lateral views of the thorax of a dog with hyperinflation of the left cranial lung lobe. (a) The left cranial lung lobe (white arrows) is hyperinflated with displacement of the trachea to the right (black arrows). The mediastinal shift is marked such that there is incomplete inflation of the right cranial lung lobe with the tip only reaching the third intercostal space. The hyperinflated lobe lacks lung and vascular markings (*), indicating emphysema. (b) The hyperinflated left cranial lobe (solid white arrows) and the cranial lobar vessels (dashed white arrow) are visible. The emphysematous changes were due to a ‘ball valve’ effect of chronic distortion and inflammation of the left cranial lobe bronchus. O = air-filled oesophagus.

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5.54

(a) Right lateral and (b) DV views of the thorax of a dog with aspiration pneumonia. The caudal part of the left cranial lung lobe is consolidated (arrowheads) and an alveolar pattern with air bronchograms (*) is visible on both views. It is important to take both right and left lateral views in cases of suspected aspiration pneumonia (as the changes are not so evident when in the dependent lung). © 2013 British Small Animal Veterinary Association

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5.54 (a) Right lateral and (b) DV views of the thorax of a dog with aspiration pneumonia. The caudal part of the left cranial lung lobe is consolidated (arrowheads) and an alveolar pattern with air bronchograms (*) is visible on both views. It is important to take both right and left lateral views in cases of suspected aspiration pneumonia (as the changes are not so evident when in the dependent lung).

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5.55

(a) Right lateral and (b) DV views of the thorax of a young dog with non-cardiogenic oedema. The lateral view shows the predominantly caudodorsal distribution (arrowed) of the alveolar infiltrate. On the DV view, the changes are bilateral but the right lung is more affected than the left lung. The thymus is visible cranial and to the left of the cardiac silhouette. © 2013 British Small Animal Veterinary Association

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5.55 (a) Right lateral and (b) DV views of the thorax of a young dog with non-cardiogenic oedema. The lateral view shows the predominantly caudodorsal distribution (arrowed) of the alveolar infiltrate. On the DV view, the changes are bilateral but the right lung is more affected than the left lung. The thymus is visible cranial and to the left of the cardiac silhouette.

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5.56

(a) Right lateral and (b) DV views of the thorax of a dog with a lung mass (histiocytic sarcoma). The well defined mass in the right caudal lung lobe (arrowheads) is in contact with the cardiac silhouette, resulting in border effacement. Several secondary nodules (arrowed) are visible in the cranial lung on the right lateral view, and on the DV view a nodule is visible overlying the left hemidiaphragm. © 2013 British Small Animal Veterinary Association

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5.56 (a) Right lateral and (b) DV views of the thorax of a dog with a lung mass (histiocytic sarcoma). The well defined mass in the right caudal lung lobe (arrowheads) is in contact with the cardiac silhouette, resulting in border effacement. Several secondary nodules (arrowed) are visible in the cranial lung on the right lateral view, and on the DV view a nodule is visible overlying the left hemidiaphragm.

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5.57

Left lateral thoracic view of a dog with torsion of the right middle lung lobe. The right middle lung lobe is consolidated (white arrows). The distal lobar bronchus appears as an air bronchogram but ends bluntly (black arrow) over the cardiac silhouette, and the proximal bronchus cannot be identified. A moderate volume of pleural effusion is present with retraction of the lung lobes, and fissure lines are also present. Blunt termination of a lobar bronchus, supported by other findings, indicates lung lobe torsion. © 2013 British Small Animal Veterinary Association

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5.57 Left lateral thoracic view of a dog with torsion of the right middle lung lobe. The right middle lung lobe is consolidated (white arrows). The distal lobar bronchus appears as an air bronchogram but ends bluntly (black arrow) over the cardiac silhouette, and the proximal bronchus cannot be identified. A moderate volume of pleural effusion is present with retraction of the lung lobes, and fissure lines are also present. Blunt termination of a lobar bronchus, supported by other findings, indicates lung lobe torsion.

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5.58

(a) DV, (b) left lateral and (c) magnified left lateral views of the thorax of a Pug with torsion of the right cranial and middle lung lobes. Pleural effusion (double-headed arrows) with retraction of the lung lobes is present on both the left and right sides. The volume of effusion is considerably larger on the right side, especially in the cranial thorax. The right cranial and middle lung lobes cannot be identified. They are consolidated and indistinguishable from the pleural fluid that has collected around the diseased lung lobe (*). On the left lateral view, the affected lobes have an indistinct vesicular or ‘bubbly’ appearance (white arrows). Asymmetrical pleural effusion, unequal collapse of the lung lobes within the ipsilateral hemithorax and a vesicular pattern are suggestive of lung lobe torsion. Although deep-chested breeds are typically associated with lung lobe torsion, chondrodystrophic small-breed dogs may also be affected. © 2013 British Small Animal Veterinary Association

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5.58 (a) DV, (b) left lateral and (c) magnified left lateral views of the thorax of a Pug with torsion of the right cranial and middle lung lobes. Pleural effusion (double-headed arrows) with retraction of the lung lobes is present on both the left and right sides. The volume of effusion is considerably larger on the right side, especially in the cranial thorax. The right cranial and middle lung lobes cannot be identified. They are consolidated and indistinguishable from the pleural fluid that has collected around the diseased lung lobe (*). On the left lateral view, the affected lobes have an indistinct vesicular or ‘bubbly’ appearance (white arrows). Asymmetrical pleural effusion, unequal collapse of the lung lobes within the ipsilateral hemithorax and a vesicular pattern are suggestive of lung lobe torsion. Although deep-chested breeds are typically associated with lung lobe torsion, chondrodystrophic small-breed dogs may also be affected.

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5.59

(a) Right lateral and (b) DV views of the thorax of a dog with a marked bronchial pattern. Note the thickened bronchial walls, seen as ‘tramlines’ (arrowheads) and ‘doughnuts’ (arrowed) that extend out to the periphery of the lungs. © 2013 British Small Animal Veterinary Association

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5.59 (a) Right lateral and (b) DV views of the thorax of a dog with a marked bronchial pattern. Note the thickened bronchial walls, seen as ‘tramlines’ (arrowheads) and ‘doughnuts’ (arrowed) that extend out to the periphery of the lungs.

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5.60

(a) Right lateral and (b) VD views of the thorax of a dog with chronic lower airway disease. There is a diffuse bronchial pattern with thickened bronchial walls, which appear as ‘doughnuts’ in cross-section (arrowed) and ‘tramlines’ in longitudinal sections (arrowheads). ‘Doughnuts’ are best recognized on the VD view and ‘tramlines’ on the lateral view. © 2013 British Small Animal Veterinary Association

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5.60 (a) Right lateral and (b) VD views of the thorax of a dog with chronic lower airway disease. There is a diffuse bronchial pattern with thickened bronchial walls, which appear as ‘doughnuts’ in cross-section (arrowed) and ‘tramlines’ in longitudinal sections (arrowheads). ‘Doughnuts’ are best recognized on the VD view and ‘tramlines’ on the lateral view.

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5.61

(a) Right lateral and (b) DV views of the thorax of a cat with chronic allergic airway disease (‘feline asthma’). Note the diffuse bronchial pattern, which in places appears nodular (arrowed) due to a combination of peribronchial thickening and the accumulation of mucus within the bronchial lumen. The margin of the cardiac silhouette is indistinct due to the large amount of pericardial fat. © 2013 British Small Animal Veterinary Association

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5.61 (a) Right lateral and (b) DV views of the thorax of a cat with chronic allergic airway disease (‘feline asthma’). Note the diffuse bronchial pattern, which in places appears nodular (arrowed) due to a combination of peribronchial thickening and the accumulation of mucus within the bronchial lumen. The margin of the cardiac silhouette is indistinct due to the large amount of pericardial fat.

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5.62

(a) Right lateral and (b) DV views of the thorax of a dog with bronchiectasis. The bronchial lumina appear widened (arrowheads) right out to the periphery of the lung. In places (e.g. over the cardiac silhouette) they have a sacculated or segmented appearance (arrowed). Areas of more homogeneous soft tissue opacity (*) are likely to represent trapped or pooled secretions and areas of secondary bronchopneumonia. Emphysematous changes are recognized as coalescing areas with a soap-bubble appearance. © 2013 British Small Animal Veterinary Association

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5.62 (a) Right lateral and (b) DV views of the thorax of a dog with bronchiectasis. The bronchial lumina appear widened (arrowheads) right out to the periphery of the lung. In places (e.g. over the cardiac silhouette) they have a sacculated or segmented appearance (arrowed). Areas of more homogeneous soft tissue opacity (*) are likely to represent trapped or pooled secretions and areas of secondary bronchopneumonia. Emphysematous changes are recognized as coalescing areas with a soap-bubble appearance.

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5.63

(a) DV thoracic radiograph of a dog with a bronchial foreign body. There is a poorly circumscribed infiltrate or increased soft tissue opacity (arrowed) surrounding the right caudal mainstem bronchus. Careful comparison with the left mainstem bronchus highlights the difference. (b) Lateral thoracic radiograph and (c) CT image of a dog with a bronchial foreign body. (b) Little change, other than mild bronchial thickening (arrowed) is appreciated on this view. (c) Comparison with the CT image is helpful to understand the radiographic changes. Inhaled foreign bodies (*) tend to result in marked bronchial thickening (arrowhead), accumulation of discharge within the bronchus and a localized peribronchial interstitial infiltrate (arrowed). Lobar consolidation and pleural effusion are uncommon, although the foreign body may migrate caudally along the diaphragmatic crurae into the retroperitoneal space. © 2013 British Small Animal Veterinary Association

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5.63 (a) DV thoracic radiograph of a dog with a bronchial foreign body. There is a poorly circumscribed infiltrate or increased soft tissue opacity (arrowed) surrounding the right caudal mainstem bronchus. Careful comparison with the left mainstem bronchus highlights the difference. (b) Lateral thoracic radiograph and (c) CT image of a dog with a bronchial foreign body. (b) Little change, other than mild bronchial thickening (arrowed) is appreciated on this view. (c) Comparison with the CT image is helpful to understand the radiographic changes. Inhaled foreign bodies (*) tend to result in marked bronchial thickening (arrowhead), accumulation of discharge within the bronchus and a localized peribronchial interstitial infiltrate (arrowed). Lobar consolidation and pleural effusion are uncommon, although the foreign body may migrate caudally along the diaphragmatic crurae into the retroperitoneal space.

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5.64

Lateral thoracic radiographs illustrating the vertebral heart score (VHS). (a) Normal heart. VHS = 5.75 (long axis) + 4.75 (short axis) = 10.5. (b) Cardiomegaly. VHS = 7.5 (long axis) + 5.25 (short axis) = 12.75. The long axis measurement is made from the ventral aspect of the left cranial lobe bronchus (note that although this is often referred to as the ‘carina’ or tracheal bifurcation, the carina can only be recognized on the DV view) to the apex. The short axis measurement is made by measuring the widest dimension of the cardiac silhouette, perpendicular to the long axis measurement. © 2013 British Small Animal Veterinary Association

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5.64 Lateral thoracic radiographs illustrating the vertebral heart score (VHS). (a) Normal heart. VHS = 5.75 (long axis) + 4.75 (short axis) = 10.5. (b) Cardiomegaly. VHS = 7.5 (long axis) + 5.25 (short axis) = 12.75. The long axis measurement is made from the ventral aspect of the left cranial lobe bronchus (note that although this is often referred to as the ‘carina’ or tracheal bifurcation, the carina can only be recognized on the DV view) to the apex. The short axis measurement is made by measuring the widest dimension of the cardiac silhouette, perpendicular to the long axis measurement.

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5.65

(a) Right lateral and (b) DV views of the thorax of a dog with left-sided cardiomegaly secondary to subaortic stenosis. The cardiac silhouette is tall on the lateral view with a bulge craniodorsally (arrowheads) in the region of the aortic arch, elevating the terminal trachea. The left atrium (arrowed) is enlarged, resulting in straightening of the caudal border of the cardiac silhouette. On the DV view, the cardiac silhouette is elongated (double-headed arrow). The typical enlargement of the aortic arch at the 11–1 o’clock position is not clearly seen in this case due to superimposition on the spine. © 2013 British Small Animal Veterinary Association

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5.65 (a) Right lateral and (b) DV views of the thorax of a dog with left-sided cardiomegaly secondary to subaortic stenosis. The cardiac silhouette is tall on the lateral view with a bulge craniodorsally (arrowheads) in the region of the aortic arch, elevating the terminal trachea. The left atrium (arrowed) is enlarged, resulting in straightening of the caudal border of the cardiac silhouette. On the DV view, the cardiac silhouette is elongated (double-headed arrow). The typical enlargement of the aortic arch at the 11–1 o’clock position is not clearly seen in this case due to superimposition on the spine.

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5.66

(a) Right lateral and (b) DV views of the thorax of a dog with cardiomegaly secondary to a patent ductus arteriosus. (a) The cardiac silhouette is wide and tall (generalized cardiomegaly). The caudal border is straightened due to left atrial enlargement (white arrow) and the cranial lobe pulmonary artery and vein are both enlarged (pulmonary overcirculation) (black double-headed arrows). (b) The cardiac silhouette is elongated. The enlargement of the aorta (A), pulmonary artery (PA) and left auricular appendage (LAA) (‘three knuckles’) is mild in this case. © 2013 British Small Animal Veterinary Association

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5.66 (a) Right lateral and (b) DV views of the thorax of a dog with cardiomegaly secondary to a patent ductus arteriosus. (a) The cardiac silhouette is wide and tall (generalized cardiomegaly). The caudal border is straightened due to left atrial enlargement (white arrow) and the cranial lobe pulmonary artery and vein are both enlarged (pulmonary overcirculation) (black double-headed arrows). (b) The cardiac silhouette is elongated. The enlargement of the aorta (A), pulmonary artery (PA) and left auricular appendage (LAA) (‘three knuckles’) is mild in this case.

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5.67

(a) Right lateral and (b) DV views of the thorax of a dog with predominantly left-sided cardiomegaly due to degenerative mitral valve disease. On the lateral view, the caudal border of the cardiac silhouette is straightened, there is ‘tenting’ of the left atrium (arrowed) and the trachea is markedly elevated. On the DV view, there is a bulge on the left side of the cardiac silhouette in the region of the left auricular appendage (arrowheads) and rounding of the cardiac apex (*), which is displaced to the right. © 2013 British Small Animal Veterinary Association

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5.67 (a) Right lateral and (b) DV views of the thorax of a dog with predominantly left-sided cardiomegaly due to degenerative mitral valve disease. On the lateral view, the caudal border of the cardiac silhouette is straightened, there is ‘tenting’ of the left atrium (arrowed) and the trachea is markedly elevated. On the DV view, there is a bulge on the left side of the cardiac silhouette in the region of the left auricular appendage (arrowheads) and rounding of the cardiac apex (*), which is displaced to the right.

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5.68

(a) Right lateral and (b) DV views of the thorax of a dog with right-sided cardiomegaly secondary to pulmonic stenosis. On the lateral view, the cardiac silhouette is wide and rounded craniodorsally (arrowhead) due to post-stenotic dilatation of the pulmonary artery. There is also increased sternal contact (arrowed). On the DV view, the cardiac silhouette has the characteristic ‘reverse D’ shape (arrowheads). Post-stenotic dilatation of the pulmonary artery has resulted in a bulge (arrowed) at the 1–2 o’clock position. In cases with less severe stenosis, the radiographic changes may be limited, with enlargement of the main pulmonary artery on the DV view being the only radiographic abnormality. © 2013 British Small Animal Veterinary Association

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5.68 (a) Right lateral and (b) DV views of the thorax of a dog with right-sided cardiomegaly secondary to pulmonic stenosis. On the lateral view, the cardiac silhouette is wide and rounded craniodorsally (arrowhead) due to post-stenotic dilatation of the pulmonary artery. There is also increased sternal contact (arrowed). On the DV view, the cardiac silhouette has the characteristic ‘reverse D’ shape (arrowheads). Post-stenotic dilatation of the pulmonary artery has resulted in a bulge (arrowed) at the 1–2 o’clock position. In cases with less severe stenosis, the radiographic changes may be limited, with enlargement of the main pulmonary artery on the DV view being the only radiographic abnormality.

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5.69

(a) Right lateral and (b) DV views of the thorax of a West Highland White Terrier with pulmonary fibrosis and predominantly right-sided cardiomegaly. On the lateral view, the cardiac silhouette is wide with the apex elevated from the sternum (arrowhead). On the DV view, the cardiac silhouette has a characteristic ‘reverse D’ shape due to right heart enlargement (arrowheads). The lung fields show a diffuse mixed interstitial and alveolar opacity (*) with some pleural lines visible between the lung lobes. The cranial mediastinum is widened on the DV view, probably due to fat. © 2013 British Small Animal Veterinary Association

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5.69 (a) Right lateral and (b) DV views of the thorax of a West Highland White Terrier with pulmonary fibrosis and predominantly right-sided cardiomegaly. On the lateral view, the cardiac silhouette is wide with the apex elevated from the sternum (arrowhead). On the DV view, the cardiac silhouette has a characteristic ‘reverse D’ shape due to right heart enlargement (arrowheads). The lung fields show a diffuse mixed interstitial and alveolar opacity (*) with some pleural lines visible between the lung lobes. The cranial mediastinum is widened on the DV view, probably due to fat.

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5.70

(a) Right lateral and (b) DV views of the thorax of a dog with generalized cardiomegaly. The cardiac silhouette is both wide and tall. Specific chamber enlargement is not visible. The vertebral heart score = 12.5. Differential diagnoses for this appearance include congenital heart disease, pericardial disease, dilated cardiomyopathy, degenerative valvular disease and secondary to chronic anaemia or bradycardia. © 2013 British Small Animal Veterinary Association

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5.70 (a) Right lateral and (b) DV views of the thorax of a dog with generalized cardiomegaly. The cardiac silhouette is both wide and tall. Specific chamber enlargement is not visible. The vertebral heart score = 12.5. Differential diagnoses for this appearance include congenital heart disease, pericardial disease, dilated cardiomyopathy, degenerative valvular disease and secondary to chronic anaemia or bradycardia.

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5.71

(a) Right lateral and (b) DV views of the thorax of a cat with cardiomegaly secondary to hypertrophic cardiomyopathy. The cardiac silhouette is enlarged and tall. The caudal vena cava is elevated and the dorsal third of the cardiac silhouette is widened (arrowheads). The increase in width is better appreciated on the DV view, where the cranial aspect of the cardiac silhouette occupies most of the width of the thoracic cavity. © 2013 British Small Animal Veterinary Association

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5.71 (a) Right lateral and (b) DV views of the thorax of a cat with cardiomegaly secondary to hypertrophic cardiomyopathy. The cardiac silhouette is enlarged and tall. The caudal vena cava is elevated and the dorsal third of the cardiac silhouette is widened (arrowheads). The increase in width is better appreciated on the DV view, where the cranial aspect of the cardiac silhouette occupies most of the width of the thoracic cavity.

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5.72

Lateral view of the thorax of a dog with microcardia as a result of hypoadrenocorticism. The cardiac silhouette is small and narrowed and displaced from the sternum by air-filled lung. The cranial lobar pulmonary vessels (arrowhead) are thin/thready and the lung parenchyma is generally more lucent in appearance due to hypovolaemia (undercirculation). © 2013 British Small Animal Veterinary Association

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5.72 Lateral view of the thorax of a dog with microcardia as a result of hypoadrenocorticism. The cardiac silhouette is small and narrowed and displaced from the sternum by air-filled lung. The cranial lobar pulmonary vessels (arrowhead) are thin/thready and the lung parenchyma is generally more lucent in appearance due to hypovolaemia (undercirculation).

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5.73

(a) Right lateral and (b) DV views of the thorax of a dog with a heart base mass. The terminal trachea (white arrowheads) is elevated dorsally on the lateral view and deviated to the right on the DV view. Retraction of the lung lobes from the thoracic wall (black arrowheads) by a soft tissue opacity and blurring of the margins of the cardiac silhouette indicate that pleural effusion is present. The ground glass appearance and distension of the cranioventral abdomen indicate ascites. For comparison, (c) and (d) are orthogonal views of a cat with a perihilar mass due to tracheobronchial lymphadenopathy as a result of a lung mass (*) in a caudal lobe. On the lateral view, the perihilar mass (arrowheads) is well marginated and is seen both ventral and dorsal to the terminal trachea and mainstem bronchi. There is no deviation of the terminal trachea. The DV view provides little information about the perihilar mass, but clearly shows severe volume loss and some consolidation of the left caudal lung lobe with a mediastinal shift and cranial positioning of the left hemidiaphragm. © 2013 British Small Animal Veterinary Association

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5.73 (a) Right lateral and (b) DV views of the thorax of a dog with a heart base mass. The terminal trachea (white arrowheads) is elevated dorsally on the lateral view and deviated to the right on the DV view. Retraction of the lung lobes from the thoracic wall (black arrowheads) by a soft tissue opacity and blurring of the margins of the cardiac silhouette indicate that pleural effusion is present. The ground glass appearance and distension of the cranioventral abdomen indicate ascites. For comparison, (c) and (d) are orthogonal views of a cat with a perihilar mass due to tracheobronchial lymphadenopathy as a result of a lung mass (*) in a caudal lobe. On the lateral view, the perihilar mass (arrowheads) is well marginated and is seen both ventral and dorsal to the terminal trachea and mainstem bronchi. There is no deviation of the terminal trachea. The DV view provides little information about the perihilar mass, but clearly shows severe volume loss and some consolidation of the left caudal lung lobe with a mediastinal shift and cranial positioning of the left hemidiaphragm.

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5.74

(a) Right lateral and (b) DV views of the thorax of a cat with pericardial effusion. The cardiac silhouette is large and rounded on both views with well defined margins (arrowed). Pericardial effusion in the cat occurs secondary to primary (myocardial) cardiac disease, neoplasia (lymphoma) or infectious disease (e.g. feline coronavirus (the causative agent of feline infectious peritonitis), feline leukaemia virus, feline immunodeficiency virus and toxoplasmosis). © 2013 British Small Animal Veterinary Association

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5.74 (a) Right lateral and (b) DV views of the thorax of a cat with pericardial effusion. The cardiac silhouette is large and rounded on both views with well defined margins (arrowed). Pericardial effusion in the cat occurs secondary to primary (myocardial) cardiac disease, neoplasia (lymphoma) or infectious disease (e.g. feline coronavirus (the causative agent of feline infectious peritonitis), feline leukaemia virus, feline immunodeficiency virus and toxoplasmosis).

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5.75

Vascular pattern: enlarged pulmonary arteries. Right lateral view of the thorax of a dog with pulmonary hypertension due to Angiostrongylus vasorum infection. The increased width of the cardiac silhouette and greater sternal contact (white arrowhead) indicate moderate enlargement of the right side of the heart. Elevation of the cardiac apex (black arrowhead) is suggestive of right ventricular (concentric) hypertrophy. The left (white arrows) and right (black arrows) caudal lobar pulmonary arteries are increased in size. There is a poorly circumscribed infiltrate in the periphery of the lung lobes. This pattern of vascular and cardiac enlargement may also occur with a reverse patent ductus arteriosus and pulmonary thromboembolism. © 2013 British Small Animal Veterinary Association

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5.75 Vascular pattern: enlarged pulmonary arteries. Right lateral view of the thorax of a dog with pulmonary hypertension due to Angiostrongylus vasorum infection. The increased width of the cardiac silhouette and greater sternal contact (white arrowhead) indicate moderate enlargement of the right side of the heart. Elevation of the cardiac apex (black arrowhead) is suggestive of right ventricular (concentric) hypertrophy. The left (white arrows) and right (black arrows) caudal lobar pulmonary arteries are increased in size. There is a poorly circumscribed infiltrate in the periphery of the lung lobes. This pattern of vascular and cardiac enlargement may also occur with a reverse patent ductus arteriosus and pulmonary thromboembolism.

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5.76

Vascular pattern: enlarged pulmonary arteries and veins. Lateral view of the thorax of a dog with severe pulmonary oedema due to left-sided congestive heart failure. The cranial lobar artery (A) and vein (V) are both enlarged (double-headed white arrows) compared with the diameter of the proximal third of the fourth rib (double-headed black arrow). The pulmonary vein is subjectively larger than the pulmonary artery. Assessment of the size of the pulmonary vessels is limited by the severity of the pulmonary oedema. © 2013 British Small Animal Veterinary Association

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5.76 Vascular pattern: enlarged pulmonary arteries and veins. Lateral view of the thorax of a dog with severe pulmonary oedema due to left-sided congestive heart failure. The cranial lobar artery (A) and vein (V) are both enlarged (double-headed white arrows) compared with the diameter of the proximal third of the fourth rib (double-headed black arrow). The pulmonary vein is subjectively larger than the pulmonary artery. Assessment of the size of the pulmonary vessels is limited by the severity of the pulmonary oedema.

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5.77

(a) Right lateral and (b) DV views of the thorax of a cat with pulmonary overcirculation secondary to a ventricular septal defect. There is generalized cardiomegaly, seen on both views as a tall, wide cardiac silhouette. The cranial and caudal lobar pulmonary arteries (PA; white arrows) and pulmonary veins (PV; black arrow) are enlarged, exceeding the size of the proximal fourth rib on the lateral view and the ninth rib on the DV view at the point at which they cross. The caudal lobar vessels (both arteries and veins (CdLV)) are superimposed on the lateral view. A patchy area (*) superimposed on the caudal vena cava on the lateral view is suggestive of pulmonary oedema. © 2013 British Small Animal Veterinary Association

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5.77 (a) Right lateral and (b) DV views of the thorax of a cat with pulmonary overcirculation secondary to a ventricular septal defect. There is generalized cardiomegaly, seen on both views as a tall, wide cardiac silhouette. The cranial and caudal lobar pulmonary arteries (PA; white arrows) and pulmonary veins (PV; black arrow) are enlarged, exceeding the size of the proximal fourth rib on the lateral view and the ninth rib on the DV view at the point at which they cross. The caudal lobar vessels (both arteries and veins (CdLV)) are superimposed on the lateral view. A patchy area (*) superimposed on the caudal vena cava on the lateral view is suggestive of pulmonary oedema.

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5.78

Vascular pattern: decreased vascular size. Lateral view of the thorax of a dog with a large thrombus occluding the main pulmonary artery and the left and right pulmonary artery branches. A soft tissue band (white arrow), consistent with an enlarged proximal left main pulmonary artery, narrows abruptly. The distal caudal lobe pulmonary arteries are thinned and indistinct (*). The lung fields generally appear hyperlucent (underperfused). One of the cranial lobe pulmonary arteries (A) is reduced in size compared with the companion vein (V). The cardiac apex is elevated (black arrows) due to right ventricular hypertrophy. Note that with pulmonary thromboembolism, the appearance of the lung is variable and can be normal, hyperlucent, consolidated or reduced in size due to atelectasis. © 2013 British Small Animal Veterinary Association

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5.78 Vascular pattern: decreased vascular size. Lateral view of the thorax of a dog with a large thrombus occluding the main pulmonary artery and the left and right pulmonary artery branches. A soft tissue band (white arrow), consistent with an enlarged proximal left main pulmonary artery, narrows abruptly. The distal caudal lobe pulmonary arteries are thinned and indistinct (*). The lung fields generally appear hyperlucent (underperfused). One of the cranial lobe pulmonary arteries (A) is reduced in size compared with the companion vein (V). The cardiac apex is elevated (black arrows) due to right ventricular hypertrophy. Note that with pulmonary thromboembolism, the appearance of the lung is variable and can be normal, hyperlucent, consolidated or reduced in size due to atelectasis.

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5.79

Vascular pattern: abnormal shape. DV view of the thorax of a dog with chronic pulmonary disease secondary to chronic Angiostrongylus vasorum infection (same dog as in Figure 5.75 ). The peripheral branches of the arteries (A) terminate abruptly (arrowed). The ‘blunting’ or ‘pruning’ of the arteries in this case is due to thromboembolism, inflammatory infiltrate and pulmonary fibrosis. © 2013 British Small Animal Veterinary Association

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5.79 Vascular pattern: abnormal shape. DV view of the thorax of a dog with chronic pulmonary disease secondary to chronic Angiostrongylus vasorum infection (same dog as in Figure 5.75 ). The peripheral branches of the arteries (A) terminate abruptly (arrowed). The ‘blunting’ or ‘pruning’ of the arteries in this case is due to thromboembolism, inflammatory infiltrate and pulmonary fibrosis.

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5.80

Vascular pattern: abnormal margination. (a) Lateral and (b) DV views of the thorax of a cat with an abscess in the caudodorsal mediastinum. An oval soft tissue mass (arrowed) lies dorsal to the aorta (A) on the midline. The aorta has been displaced ventrally by the mass. The margins of the aorta at the level of the mass cannot be recognized. (Courtesy of MyVet24/7) © 2013 British Small Animal Veterinary Association

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5.80 Vascular pattern: abnormal margination. (a) Lateral and (b) DV views of the thorax of a cat with an abscess in the caudodorsal mediastinum. An oval soft tissue mass (arrowed) lies dorsal to the aorta (A) on the midline. The aorta has been displaced ventrally by the mass. The margins of the aorta at the level of the mass cannot be recognized. (Courtesy of MyVet24/7)

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5.81

Vascular pattern: abnormal location. Lateral views of the thorax of a deep-chested dog with pleural effusion (a) before and (b) following drainage. (a) The lung lobes are retracted as a result of the pleural effusion. The left cranial lung lobe has rotated caudally such that the cranial tip of the lobe (black arrow) lies dorsal to the sixth sternebra. The cranial lobar vessels are kinked and redirected caudally (white arrows). There are no changes (consolidation, emphysema) within the lobe to suggest that torsion has occurred. (b) Following drainage, the lobe (black arrow) and lobar vessels (white arrows) have returned to their normal position and location. © 2013 British Small Animal Veterinary Association

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5.81 Vascular pattern: abnormal location. Lateral views of the thorax of a deep-chested dog with pleural effusion (a) before and (b) following drainage. (a) The lung lobes are retracted as a result of the pleural effusion. The left cranial lung lobe has rotated caudally such that the cranial tip of the lobe (black arrow) lies dorsal to the sixth sternebra. The cranial lobar vessels are kinked and redirected caudally (white arrows). There are no changes (consolidation, emphysema) within the lobe to suggest that torsion has occurred. (b) Following drainage, the lobe (black arrow) and lobar vessels (white arrows) have returned to their normal position and location.

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5.82

(a) Right lateral and (b) DV views of the thorax of a dog with bilateral pleural effusion. Note the elevation of the ventral borders of the lung lobes (arrowed), with ‘scalloping’ of the edges, on the lateral view. The ventral border of the diaphragm (*) is obscured by fluid. The border of the cardiac silhouette is faintly visible as it is outlined by a thin strip of pericardial fat. There are classic fissure lines (arrowheads) visible bilaterally in the seventh intercostal spaces; these are seen more clearly on the DV view. © 2013 British Small Animal Veterinary Association

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5.82 (a) Right lateral and (b) DV views of the thorax of a dog with bilateral pleural effusion. Note the elevation of the ventral borders of the lung lobes (arrowed), with ‘scalloping’ of the edges, on the lateral view. The ventral border of the diaphragm (*) is obscured by fluid. The border of the cardiac silhouette is faintly visible as it is outlined by a thin strip of pericardial fat. There are classic fissure lines (arrowheads) visible bilaterally in the seventh intercostal spaces; these are seen more clearly on the DV view.

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5.83

Right lateral views of the thorax of a cat (a) before and (b) following therapeutic thoracocentesis. (a) Note that despite the moderately large volume of pleural fluid, both caudal lung lobes are only partially collapsed and have a rounded appearance. One of the lobes (white arrows) is more markedly affected than the other (black arrow). A small volume of free air is present (*) following previous thoracocentesis. (b) Following drainage, the shape and volume of the lung lobes is unchanged, indicating chronic pleural thickening or cortication. © 2013 British Small Animal Veterinary Association

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5.83 Right lateral views of the thorax of a cat (a) before and (b) following therapeutic thoracocentesis. (a) Note that despite the moderately large volume of pleural fluid, both caudal lung lobes are only partially collapsed and have a rounded appearance. One of the lobes (white arrows) is more markedly affected than the other (black arrow). A small volume of free air is present (*) following previous thoracocentesis. (b) Following drainage, the shape and volume of the lung lobes is unchanged, indicating chronic pleural thickening or cortication.

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5.84

(a) Right lateral and (b) DV views of the thorax of a dog with pneumothorax secondary to a lung bulla. On the lateral view, the cardiac silhouette is elevated by a gas opacity. The wall of a bulla (arrowheads) is visible as a curvilinear opacity dorsal to the carina. The oval soft tissue opacity superimposed on the heart was thought to represent a fluid-filled bleb. On the DV view, the bleb (arrowheads) is clearly seen to the left of the cardiac silhouette, but the bulla is not visible. © 2013 British Small Animal Veterinary Association

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5.84 (a) Right lateral and (b) DV views of the thorax of a dog with pneumothorax secondary to a lung bulla. On the lateral view, the cardiac silhouette is elevated by a gas opacity. The wall of a bulla (arrowheads) is visible as a curvilinear opacity dorsal to the carina. The oval soft tissue opacity superimposed on the heart was thought to represent a fluid-filled bleb. On the DV view, the bleb (arrowheads) is clearly seen to the left of the cardiac silhouette, but the bulla is not visible.

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5.85

(a) Right lateral and (b) DV views of the thorax of a dog with spontaneous pneumothorax. On the lateral view, the heart is raised from the sternum by a gas opacity and there is free gas between the caudodorsal lung margins and the spine (double-headed arrows). The DV view allows the changes to be lateralized, and shows that the pneumothorax is worse on the left-hand side. The caudal part of the left cranial lobe and the left caudal lobe have both collapsed and are outlined by gas (*). © 2013 British Small Animal Veterinary Association

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5.85 (a) Right lateral and (b) DV views of the thorax of a dog with spontaneous pneumothorax. On the lateral view, the heart is raised from the sternum by a gas opacity and there is free gas between the caudodorsal lung margins and the spine (double-headed arrows). The DV view allows the changes to be lateralized, and shows that the pneumothorax is worse on the left-hand side. The caudal part of the left cranial lobe and the left caudal lobe have both collapsed and are outlined by gas (*).

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5.86

(a) Right lateral and (b) DV views of the thorax of a cat with pneumohydrothorax. The lateral view shows consolidation of a lung lobe (with a lobar sign) over the cardiac silhouette (*) and a generalized increase in opacity within the thorax, indicative of pleural effusion. Several bubbles of free gas (arrowed) are visible caudoventrally over the cardiac apex and caudodorsally around the retracted lung lobes. On the DV view, the cardiac silhouette is effaced by the fluid and the free gas is more difficult to recognize, except focally on the left-hand side (arrowed). Classic ‘fluid lines’, demonstrating a fluid–gas interface, are only seen if a horizontal beam is used. © 2013 British Small Animal Veterinary Association

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5.86 (a) Right lateral and (b) DV views of the thorax of a cat with pneumohydrothorax. The lateral view shows consolidation of a lung lobe (with a lobar sign) over the cardiac silhouette (*) and a generalized increase in opacity within the thorax, indicative of pleural effusion. Several bubbles of free gas (arrowed) are visible caudoventrally over the cardiac apex and caudodorsally around the retracted lung lobes. On the DV view, the cardiac silhouette is effaced by the fluid and the free gas is more difficult to recognize, except focally on the left-hand side (arrowed). Classic ‘fluid lines’, demonstrating a fluid–gas interface, are only seen if a horizontal beam is used.

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5.87

DV view of the thorax of a dog with a mediastinal shift to the right. The right middle lung lobe has collapsed and the cardiac silhouette is displaced to the right (arrowed). The right hemidiaphragm is cranially displaced (arrowheads). Although mediastinal shift is a physiological change, it prevents assessment of the collapsed area of lung and therefore repeat inspiratory radiographs should be obtained. © 2013 British Small Animal Veterinary Association

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5.87 DV view of the thorax of a dog with a mediastinal shift to the right. The right middle lung lobe has collapsed and the cardiac silhouette is displaced to the right (arrowed). The right hemidiaphragm is cranially displaced (arrowheads). Although mediastinal shift is a physiological change, it prevents assessment of the collapsed area of lung and therefore repeat inspiratory radiographs should be obtained.

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5.88

(a) Right lateral and (b) DV views of the thorax of a dog with a cranial mediastinal mass. On the lateral view, the mass (arrowheads) lies in the cranioventral thorax and is of homogeneous soft tissue opacity. Note that the mass has elevated the trachea and displaced the cranial lung lobes caudally. On the DV view, the mass (arrowheads) lies on the midline resulting in widening of the cranial mediastinum. The prominent skin folds (arrowed) should not be overinterpreted as pneumothorax. © 2013 British Small Animal Veterinary Association

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5.88 (a) Right lateral and (b) DV views of the thorax of a dog with a cranial mediastinal mass. On the lateral view, the mass (arrowheads) lies in the cranioventral thorax and is of homogeneous soft tissue opacity. Note that the mass has elevated the trachea and displaced the cranial lung lobes caudally. On the DV view, the mass (arrowheads) lies on the midline resulting in widening of the cranial mediastinum. The prominent skin folds (arrowed) should not be overinterpreted as pneumothorax.

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5.89

(a) Right lateral and (b) DV views of the thorax of a dog with a caudal mediastinal mass. On the lateral view, the mass is superimposed on the caudal lung, extending dorsally from the level of the caudal vena cava. The DV view localizes the mass (arrowheads) to the midline, making a caudal mediastinal location more likely. Accessory lung lobe masses can also have a midline location, but are usually positioned more ventrally. On ultrasound examination, the mass had a fluid-filled centre and a paraoesophageal mass was found at exploratory thoracotomy. © 2013 British Small Animal Veterinary Association

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5.89 (a) Right lateral and (b) DV views of the thorax of a dog with a caudal mediastinal mass. On the lateral view, the mass is superimposed on the caudal lung, extending dorsally from the level of the caudal vena cava. The DV view localizes the mass (arrowheads) to the midline, making a caudal mediastinal location more likely. Accessory lung lobe masses can also have a midline location, but are usually positioned more ventrally. On ultrasound examination, the mass had a fluid-filled centre and a paraoesophageal mass was found at exploratory thoracotomy.

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5.90

(a) Right lateral and (b) DV views of the thorax of a dog with marked mediastinal and tracheobronchial lymphadenopathy due to granulomatous lymphadenitis. The middle tracheobronchial lymph node (M) is markedly enlarged (black arrows). It appears as a large, indistinctly marginated, soft tissue opacity caudal to the carina on the lateral view. On the DV view, the lymphadenopathy has resulted in lateral displacement and compression of the mainstem bronchi. The location of the right (R) and left (L) tracheobronchial lymph nodes is shown. Note there is also marked enlargement of the cranial mediastinal/sternal lymph nodes (white arrows), but only slight tracheal elevation. © 2013 British Small Animal Veterinary Association

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5.90 (a) Right lateral and (b) DV views of the thorax of a dog with marked mediastinal and tracheobronchial lymphadenopathy due to granulomatous lymphadenitis. The middle tracheobronchial lymph node (M) is markedly enlarged (black arrows). It appears as a large, indistinctly marginated, soft tissue opacity caudal to the carina on the lateral view. On the DV view, the lymphadenopathy has resulted in lateral displacement and compression of the mainstem bronchi. The location of the right (R) and left (L) tracheobronchial lymph nodes is shown. Note there is also marked enlargement of the cranial mediastinal/sternal lymph nodes (white arrows), but only slight tracheal elevation.

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5.91

Lateral view of the thorax of a cat with pneumomediastinum secondary to dyspnoea (as a result of congestive heart failure). The heart is enlarged, although the pulmonary oedema has largely resolved. Note the heterogeneous appearance of the cranial mediastinum, with gas highlighting the longus colli muscles (*) and dorsal tracheal wall (arrowed), and extending ventral to the trachea to outline the brachiocephalic trunk (B) and cranial vena cava (CrVC). Note also the delineation of the right azygos vein (Az) cranial and dorsal to the aorta (A). © 2013 British Small Animal Veterinary Association

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5.91 Lateral view of the thorax of a cat with pneumomediastinum secondary to dyspnoea (as a result of congestive heart failure). The heart is enlarged, although the pulmonary oedema has largely resolved. Note the heterogeneous appearance of the cranial mediastinum, with gas highlighting the longus colli muscles (*) and dorsal tracheal wall (arrowed), and extending ventral to the trachea to outline the brachiocephalic trunk (B) and cranial vena cava (CrVC). Note also the delineation of the right azygos vein (Az) cranial and dorsal to the aorta (A).

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5.92

(a) Right lateral and (b) DV views of a cat with extensive subcutaneous emphysema, pneumomediastinum and pneumoretroperitoneum (R). The presence of subcutaneous air (double-headed arrows) complicates interpretation of thoracic radiographs as the gas lucencies are superimposed on the thorax. © 2013 British Small Animal Veterinary Association

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5.92 (a) Right lateral and (b) DV views of a cat with extensive subcutaneous emphysema, pneumomediastinum and pneumoretroperitoneum (R). The presence of subcutaneous air (double-headed arrows) complicates interpretation of thoracic radiographs as the gas lucencies are superimposed on the thorax.

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5.93

(a) Right lateral and (b) DV views of the thorax of a dog with fractures of the sixth and seventh ribs (arrowheads) on the left-hand side and a unilateral pneumothorax. The fractures are easy to recognize on the DV view but are less obvious on the lateral view, due to a combination of the proximal location of the fracture and radiographic factors (rotation and some movement blur). © 2013 British Small Animal Veterinary Association

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5.93 (a) Right lateral and (b) DV views of the thorax of a dog with fractures of the sixth and seventh ribs (arrowheads) on the left-hand side and a unilateral pneumothorax. The fractures are easy to recognize on the DV view but are less obvious on the lateral view, due to a combination of the proximal location of the fracture and radiographic factors (rotation and some movement blur).

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5.94

(a) Right lateral and (b) DV views of the thorax of a dog with a rib tumour. The DV view is required to localize the large soft tissue mass (white arrows) seen on the lateral view. The mass has created an ‘extrapleural’ sign (i.e. the lung is pushed away by the mass, which has a broad base at the periphery of the thorax) (black arrows). The rib destruction and periosteal reaction (arrowhead) is easily overlooked on the lateral view. © 2013 British Small Animal Veterinary Association

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5.94 (a) Right lateral and (b) DV views of the thorax of a dog with a rib tumour. The DV view is required to localize the large soft tissue mass (white arrows) seen on the lateral view. The mass has created an ‘extrapleural’ sign (i.e. the lung is pushed away by the mass, which has a broad base at the periphery of the thorax) (black arrows). The rib destruction and periosteal reaction (arrowhead) is easily overlooked on the lateral view.

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5.95

Left lateral view of the thorax of a dog with a congenital sternal anomaly. The fourth to sixth sternebrae are fused. The caudal sternum is angled dorsally and the costal arch is deformed. © 2013 British Small Animal Veterinary Association

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5.95 Left lateral view of the thorax of a dog with a congenital sternal anomaly. The fourth to sixth sternebrae are fused. The caudal sternum is angled dorsally and the costal arch is deformed.

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5.96

(a) Right lateral and (b) DV views of the thorax of a cat with a diaphragmatic rupture. (a) The position of the stomach (S) is abnormal. It is gas-filled and displaced cranially. The soft tissue opacity (arrowed) in the caudal thorax effaces the caudal border of the cardiac silhouette and the cranioventral diaphragm. It is lobulated in appearance, representing displaced liver and probably spleen as well. A small volume of pleural fluid can be seen elevating the cranial lung lobes. Subcutaneous emphysema is present ventral to the cranial sternum. (b) A triangular soft tissue opacity (arrowed), probably the spleen, lies between the left chest wall and the cardiac silhouette, with a rounded soft tissue opacity, probably the liver, present on the right. H = cardiac silhouette; L = liver. © 2013 British Small Animal Veterinary Association

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5.96 (a) Right lateral and (b) DV views of the thorax of a cat with a diaphragmatic rupture. (a) The position of the stomach (S) is abnormal. It is gas-filled and displaced cranially. The soft tissue opacity (arrowed) in the caudal thorax effaces the caudal border of the cardiac silhouette and the cranioventral diaphragm. It is lobulated in appearance, representing displaced liver and probably spleen as well. A small volume of pleural fluid can be seen elevating the cranial lung lobes. Subcutaneous emphysema is present ventral to the cranial sternum. (b) A triangular soft tissue opacity (arrowed), probably the spleen, lies between the left chest wall and the cardiac silhouette, with a rounded soft tissue opacity, probably the liver, present on the right. H = cardiac silhouette; L = liver.

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5.97

(a) Right lateral view of the thorax of a dog with a PPDH. The cardiac silhouette is markedly enlarged. Mixed opacities superimposed on the cardiac silhouette on both views localize these structures to within the pericardium. These opacities include areas of fat, linear gas opacities representing small intestinal loops (I) and a larger folded gas-filled viscus representing the stomach (S). The ventral diaphragmatic line is obscured, the sternum is shortened and the xiphisternum is absent. (b) DV view of the thorax of a dog with a PPDH. The cardiac silhouette is markedly enlarged. Mixed opacities superimposed on the cardiac silhouette on both views localize these structures to within the pericardium. These opacities include areas of fat, linear gas opacities representing small intestinal loops and a larger folded gas-filled viscus representing the stomach (S). The ventral diaphragmatic line is obscured, the sternum is shortened and the xiphisternum is absent. © 2013 British Small Animal Veterinary Association

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5.97 (a) Right lateral view of the thorax of a dog with a PPDH. The cardiac silhouette is markedly enlarged. Mixed opacities superimposed on the cardiac silhouette on both views localize these structures to within the pericardium. These opacities include areas of fat, linear gas opacities representing small intestinal loops (I) and a larger folded gas-filled viscus representing the stomach (S). The ventral diaphragmatic line is obscured, the sternum is shortened and the xiphisternum is absent. (b) DV view of the thorax of a dog with a PPDH. The cardiac silhouette is markedly enlarged. Mixed opacities superimposed on the cardiac silhouette on both views localize these structures to within the pericardium. These opacities include areas of fat, linear gas opacities representing small intestinal loops and a larger folded gas-filled viscus representing the stomach (S). The ventral diaphragmatic line is obscured, the sternum is shortened and the xiphisternum is absent.

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5.98

(a) Left lateral view of the thorax of a dog with signs of regurgitation and coughing. Generalized dilatation of the oesophagus is present (double-headed arrows). Caudally, the paired walls of the dilated oesophagus taper towards the diaphragm (lower oesophageal sphincter). The trachea is displaced slightly ventrally by the dilated oesophagus and the dorsal wall of the trachea (arrowhead) is recognized due to air in the oesophagus (tracheal stripe sign). Megaoesophagus is often more conspicuous on a left lateral view. (b) Right lateral view of a dog with generalized megaoesophagus, but in this patient the dilatation (white double-headed arrow) is less marked. Pooling of fluid in the caudal oesophagus is responsible for the soft tissue opacity band (white dashed headed arrow) in the caudal thorax. Note the sternal lymph node (arrowed) is enlarged. (c) Oesophageal dilatation results in ventral displacement (arrowed) of the intrathoracic trachea. The dilated oesophagus dorsal to the heart and within the caudal thorax is filled with fluid and gas. © 2013 British Small Animal Veterinary Association

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5.98 (a) Left lateral view of the thorax of a dog with signs of regurgitation and coughing. Generalized dilatation of the oesophagus is present (double-headed arrows). Caudally, the paired walls of the dilated oesophagus taper towards the diaphragm (lower oesophageal sphincter). The trachea is displaced slightly ventrally by the dilated oesophagus and the dorsal wall of the trachea (arrowhead) is recognized due to air in the oesophagus (tracheal stripe sign). Megaoesophagus is often more conspicuous on a left lateral view. (b) Right lateral view of a dog with generalized megaoesophagus, but in this patient the dilatation (white double-headed arrow) is less marked. Pooling of fluid in the caudal oesophagus is responsible for the soft tissue opacity band (white dashed headed arrow) in the caudal thorax. Note the sternal lymph node (arrowed) is enlarged. (c) Oesophageal dilatation results in ventral displacement (arrowed) of the intrathoracic trachea. The dilated oesophagus dorsal to the heart and within the caudal thorax is filled with fluid and gas.

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5.99

Lateral (standing) view of the neck of a dog with generalized megaoesophagus. A barium study has been performed (using semi-liquid food) and the contrast medium has pooled ventrally within the dilated cervical oesophagus (arrowed). Note the air dorsal to the barium (*) and the dilatation of the thoracic oesophagus. A tracheal stripe sign is evident (arrowheads). © 2013 British Small Animal Veterinary Association

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5.99 Lateral (standing) view of the neck of a dog with generalized megaoesophagus. A barium study has been performed (using semi-liquid food) and the contrast medium has pooled ventrally within the dilated cervical oesophagus (arrowed). Note the air dorsal to the barium (*) and the dilatation of the thoracic oesophagus. A tracheal stripe sign is evident (arrowheads).

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5.100

Lateral (standing) radiograph of the neck of a dog with generalized megaoesophagus and oesophageal hypomotility. The ingested barium has not formed a discrete bolus. The barium is elongated with dilatation of the oesophagus aboral to the bolus. With normal oesophageal function, a tight bolus is formed as the oesophagus maintains a high pressure area in front and behind the bolus as it is propelled along the oesophagus. © 2013 British Small Animal Veterinary Association

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5.100 Lateral (standing) radiograph of the neck of a dog with generalized megaoesophagus and oesophageal hypomotility. The ingested barium has not formed a discrete bolus. The barium is elongated with dilatation of the oesophagus aboral to the bolus. With normal oesophageal function, a tight bolus is formed as the oesophagus maintains a high pressure area in front and behind the bolus as it is propelled along the oesophagus.

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5.101

Fluoroscopic studies of oesophageal motility in (a) a normal dog and (b) a dog with oesophageal hypomotility. (a) A tight bolus (arrowed) has been propelled into the distal oesophagus. There is no oesophageal dilatation. (b) The bolus is elongated, indicating hypomotility (arrowed). © 2013 British Small Animal Veterinary Association

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5.101 Fluoroscopic studies of oesophageal motility in (a) a normal dog and (b) a dog with oesophageal hypomotility. (a) A tight bolus (arrowed) has been propelled into the distal oesophagus. There is no oesophageal dilatation. (b) The bolus is elongated, indicating hypomotility (arrowed).

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5.102

Lateral barium oesophagram of a dog with a vascular ring anomaly (persistent right aortic arch). The cervical and cranial thoracic oesophagus is markedly dilated with a barium/food mixture (white arrows). The dilated oesophagus narrows abruptly (black arrow) over the heart base. The approximate location of the ascending aorta (Ao) and main pulmonary artery (PA) are indicated. © 2013 British Small Animal Veterinary Association

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5.102 Lateral barium oesophagram of a dog with a vascular ring anomaly (persistent right aortic arch). The cervical and cranial thoracic oesophagus is markedly dilated with a barium/food mixture (white arrows). The dilated oesophagus narrows abruptly (black arrow) over the heart base. The approximate location of the ascending aorta (Ao) and main pulmonary artery (PA) are indicated.

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5.103

(a) Lateral and (b) DV views of the thorax of a cat with signs of recurrent regurgitation due to a hiatal hernia. There is a large midline soft tissue mass, consistent with herniated stomach (double-headed black arrow) in the caudodorsal thorax. The normal gas-filled stomach is not recognized. The oesophagus is dilated with air (double-headed white arrows), resulting in ventral displacement of the trachea. © 2013 British Small Animal Veterinary Association

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5.103 (a) Lateral and (b) DV views of the thorax of a cat with signs of recurrent regurgitation due to a hiatal hernia. There is a large midline soft tissue mass, consistent with herniated stomach (double-headed black arrow) in the caudodorsal thorax. The normal gas-filled stomach is not recognized. The oesophagus is dilated with air (double-headed white arrows), resulting in ventral displacement of the trachea.

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5.104

(a) Lateral and (b) DV views of the thorax of a dog with non-productive retching due to an oesophageal foreign body. The foreign body appears as a rounded soft tissue structure (arrowed) in the mid-dorsal thorax caudal to the cardiac silhouette. As the foreign body is not surrounded by gas, it cannot be distinguished from the walls of the oesophagus. On occasion, it may be difficult to recognize and distinguish mineralization of bone foreign bodies (e.g. knuckles or chop bones) from the surrounding soft tissue. © 2013 British Small Animal Veterinary Association

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5.104 (a) Lateral and (b) DV views of the thorax of a dog with non-productive retching due to an oesophageal foreign body. The foreign body appears as a rounded soft tissue structure (arrowed) in the mid-dorsal thorax caudal to the cardiac silhouette. As the foreign body is not surrounded by gas, it cannot be distinguished from the walls of the oesophagus. On occasion, it may be difficult to recognize and distinguish mineralization of bone foreign bodies (e.g. knuckles or chop bones) from the surrounding soft tissue.

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5.105

Lateral views of (a) the cervical region and (b) the thorax of a dog with perforation of the cervical oesophagus. A large area of mixed soft tissue–gas opacity (white arrows) is present ventral to the cervical vertebrae. This represents leaked gas and food material accumulated within the paraoesophageal fascia. The cervical trachea is displaced ventrally. Extensive subcutaneous emphysema (black arrows) and pneumomediastinum (*) are present. A large pleural effusion effaces the cardiac silhouette and chest drains have been placed. © 2013 British Small Animal Veterinary Association

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5.105 Lateral views of (a) the cervical region and (b) the thorax of a dog with perforation of the cervical oesophagus. A large area of mixed soft tissue–gas opacity (white arrows) is present ventral to the cervical vertebrae. This represents leaked gas and food material accumulated within the paraoesophageal fascia. The cervical trachea is displaced ventrally. Extensive subcutaneous emphysema (black arrows) and pneumomediastinum (*) are present. A large pleural effusion effaces the cardiac silhouette and chest drains have been placed.

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5.106

(a) Lateral and (b) DV views of a dog with signs of regurgitation. (a) A large rounded soft tissue mass is present in the caudodorsal thorax (long double-headed arrow). The mass has areas of indistinct mineralization of its caudodorsal and mid-ventral aspects. The oesophagus is mildly dilated cranial to the heart (short double-headed arrow). There is mild aneurysmal dilatation of the descending aorta dorsal to the carina (arrowed). The changes are due to a large mural mass associated with Spirocerca infection. (b) The DV view is important as it localizes the mass (arrowed) to the midline. © 2013 British Small Animal Veterinary Association

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5.106 (a) Lateral and (b) DV views of a dog with signs of regurgitation. (a) A large rounded soft tissue mass is present in the caudodorsal thorax (long double-headed arrow). The mass has areas of indistinct mineralization of its caudodorsal and mid-ventral aspects. The oesophagus is mildly dilated cranial to the heart (short double-headed arrow). There is mild aneurysmal dilatation of the descending aorta dorsal to the carina (arrowed). The changes are due to a large mural mass associated with Spirocerca infection. (b) The DV view is important as it localizes the mass (arrowed) to the midline.

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5.107

Lateral view of a dog with retching due to an oesophageal tumour. A discrete soft tissue mass (arrowed) is highlighted by gas in the moderately dilated terminal oesophagus. The stomach is also distended with gas. Note that the white linear structure overlying the stomach is a screen artefact. (Courtesy of MyVet24/7) © 2013 British Small Animal Veterinary Association

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5.107 Lateral view of a dog with retching due to an oesophageal tumour. A discrete soft tissue mass (arrowed) is highlighted by gas in the moderately dilated terminal oesophagus. The stomach is also distended with gas. Note that the white linear structure overlying the stomach is a screen artefact. (Courtesy of MyVet24/7)