Surgery of the mediastinum

image of Surgery of the mediastinum
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The mediastinum is the potential space between the right and left pulmonary pleural sacs that, in the normal dog or cat, contains the heart, great vessels, trachea, oesophagus, lymph nodes and thymus. This chapter covers anatomy, clinical features of mediastinal disease, evaluation of the mediastinum, pneumomediastinum, mediastinitis, mediastinal haemorrhage and neoplasia.

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Image of 16.1
16.1 A computed tomographic section (bone window) through the cranial thorax of a dog, cranial to the heart. The mediastinum at this level contains the cranial vena cava, trachea, longus colli muscles, oesophagus and primary branches of the aorta such as the brachycephalic trunk, right subclavian artery and left subclavian artery. The thymus is not visible in this dog.
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16.2 A computed tomographic section (lung window) through the caudal thorax of a dog, caudal to the heart. Note the vena cava residing in a reflection of the parietal pleura, which forms the plica venae cavae. The mediastinum attaches to the left side of the diaphragm near the ninth costochondral junction to accommodate the accessory lung lobe situated in the right hemithorax.
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16.4 Ventrodorsal thoracic radiograph of a young dog. The thymus is clearly visible as a triangular structure in the cranial mid-thorax. Note the width of the cranial mediastinum in comparison with the caudal mediastinum on this view.
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16.5 Lateral radiograph of a cat with a mediastinal thymoma. Owing to the mass effect of the neoplasm, dramatic elevation of the trachea and loss of the typical cardiac silhouette are observed. A soft tissue density occupies a large volume of the mid-thorax.
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16.6 Ventrodorsal thoracic radiograph of the same cat as in Figure 16.5 . Again, the mass effect of the neoplasm is resulting in distortion of adjacent structures. The heart and trachea have been displaced to the right with loss of the typical cardiac silhouette. A large soft tissue structure occupies the mid-thorax.
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16.7 Computed tomographic section (bone window) through the cranial thorax of a dog, cranial to the heart. A large soft tissue mass occupies the majority of the cranial thorax. No invasion of adjacent structures such as the trachea or great vessel is observed.
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16.8 Lateral radiograph of a dog with a thymoma. A soft tissue mass can be observed in the cranial thorax. Given the small size of the mass no distortion of adjacent structures is observed. Despite the relatively innocuous appearance of this mass, invasion into the cranial vena cava was demonstrated at surgery (see Figure 16.9 ).
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16.9 Intraoperative photograph of the case in Figure 16.8 . A large neoplastic embolism can be seen within the cranial vena cava.
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16.10 T2-weighted magnetic resonance image through the cranial thorax of a cat, cranial to the heart. The massive volume of the soft tissue mass makes differentiation of mass effect from invasiveness difficult. Note that blood vessels appear black because moving fluid is black on T2 images, compared with free fluid, which is white.
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16.11 Intraoperative photograph of the cat in Figures 16.5 , 16.6 and 16.10 . A midline sternotomy has been performed to gain access to the thorax and tumour.
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16.12 Gross anatomy of the thymoma removed from the cat in Figures 16.5 , 16.6 , 16.10 and 16.11 . This thymoma was not invasive. Note how the mass has conformed to the shape of the surrounding thoracic wall and adjacent heart. The pericardium has been removed with the tumour.
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