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Diagnostic imaging of the eye and orbit

image of Diagnostic imaging of the eye and orbit
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Abstract

The first step in clinical evaluation of the eye involves direct ophthalmic examination. However, there are occasions when significant extraocular disease or opacification of ocular media prevent direct visualization of intraocular structures. Under these circumstances, diagnostic imaging provides valuable information about the extent and character of the disease process. This chapters deals with radiography; ultrasonography; magnetic resonance imaging; computed tomography; imaging features of ocular disease; imaging features of orbital disease; advances in imaging technology.

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Figures

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2.3 Abnormal dacryocystorhinogram in a 7-year-old English Springer Spaniel with chronic dacryocystitis. The nasolacrimal duct is dilated and the contrast medium filling of the duct is uneven (arrowed) due to the presence of filling defects, which suggest the presence of inflammatory debris or foreign material.
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2.4 Ocular ultrasonography techniques. The transcorneal scan, in which the transducer is placed directly on to the cornea following the application of topical anaesthetic. The temporal scan, in which the transducer is placed caudodorsal to the globe. The zygomatic scan, in which the transducer is placed ventral to the zygomatic arch.
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2.5 Ultrasonograms acquired using the techniques shown in Figure 2.4 : the transcorneal approach, the temporal approach and the zygomatic approach. The anatomical structures visible in these images obtained from normal dogs are annotated.
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2.7 High-resolution ultrasonograms of the anterior segment acquired using a 20 MHz transducer. Appearance of the aqueous outflow pathways in a normal cat. A cat with congenital glaucoma and extreme narrowing and collapse of the ciliary cleft. A cat with a corneal sequestrum. The posterior surface of the echogenic sequestrum (white cross) and well defined posterior corneal echo corresponding to Descemet’s membrane (black cross) allow the depth of the sequestrum to be estimated. Thin-walled iridociliary cysts (arrowed) in the posterior chamber of a 2-year-old Golden Retriever are causing forward bowing of the posterior iris epithelium (arrowheads). CC = ciliary cleft; DM = Descemet’s membrane; I = iris; L = lens. (c–d Courtesy of E Bentley)
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2.8 Colour Doppler ultrasonogram of a 7-month-old Miniature Schnauzer with persistent hyperplastic primary vitreous and cataract. The characteristic Doppler signal at the posterior pole and within the vitreous cavity is consistent with blood flow in a patent hyaloid artery in the affected eye. (Courtesy of D Gould and G Gent)
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2.9 Normal MR images of the eyes and orbits. Dorsal T2-weighted image. Transverse T2-weighted image at the level of the globes. Transverse T2-weighted image immediately posterior to the globes. Sagittal oblique T2-weighted image aligned for the optic nerve. 1 = globe; 2 = extraocular muscles; 3 = medial orbital wall; 4 = frontal sinus; 5 = zygomatic salivary gland; 6 = medial pterygoid muscle; 7 = optic nerve.
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2.10 CT images of the normal orbit of a dog seen via a bone window and a soft tissue window. 1 = globe; 2 = medial orbital wall; 3 = nasal cavity; 4 = medial pterygoid muscle; 5 = zygomatic salivary gland.
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2.11 Globe rupture in a 12-year-old Labrador Retriever. Ultrasonogram: discontinuity of the posterior globe wall and vitreous can be observed extending into the retrobulbar space. There is also complete retinal detachment, which can be seen as a curvilinear echogenic structure. Corresponding MR image. The black arrows highlight the defect in the posterior globe wall. The red arrowheads depict the leakage of the vitreous through the defect into the retrobulbar space. The black arrowheads show the retinal detachment present.
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2.12 Ultrasonographic appearance of ocular foreign bodies. Transcorneal image of the globe in a 4-year-old Domestic Shorthaired cat showing a linear, echogenic foreign body extending into the lens. The foreign body was confirmed as a thorn. A 12-week-old English Cocker Spaniel with echogenic material present within a thickened conjunctiva, adjacent to the globe. The foreign body was confirmed as a grass seed.
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2.13 Ultrasonograms of an ocular tumour in a 9-year-old Golden Retriever. A large echogenic uveal mass can be seen displacing the lens and extending into the anterior chamber. A large blood vessel extending into the mass is identifiable with colour Doppler ultrasonography.
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2.14 Ultrasonogram of a diabetic cataract in a 6-year-old West Highland White Terrier showing increased echogenicity of the lens nucleus, cortex and capsule. The intumescent lens is enlarged and rounded in shape. Within the vitreous there are multiple echogenic foci, consistent with vitreal degeneration.
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2.15 Ultrasonographic appearance of posterior lentiglobus (LG), with distortion of the posterior lens capsular echo, in a Golden Retriever with persistent hyperplastic primary vitreous. In this dog, the lens cortex was sufficiently clear to allow the distortion of the posterior lens capsule, hyaloid artery (HA) remnant and a posterior lens capsular plaque to be identified on slit-lamp biomicroscopy. The opposite eye presented with a complete cataract and intralenticular haemorrhage.
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2.16 Ultrasonograms of lens rupture. Equatorial lens rupture in an 8-year-old Jack Russell Terrier. An echogenic nodule of material (arrowed) extends from the ventral equator of the lens. The lens itself is echogenic, consistent with cataract formation. Posterior lens capsule rupture in a 2-year-old Border Terrier with a cataract. A large volume of echogenic material is seen extending from the posterior lens into the vitreous.
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2.17 Ultrasonograms of retinal detachment. Focal bullous retinal detachment in a 6-year-old crossbred dog. A thick curvilinear echo extends into the vitreous from the posterior wall of the globe. Complete retinal detachment in a 15-year-old crossbred dog. A thick, echogenic, curvilinear structure extends from the location of the optic nerve head to the ora ciliaris retinae. The subretinal space is hypoechoic in this dog with systemic hypertension. Complete retinal detachment in a 4-year-old Labrador Retriever with endophthalmitis due to blastomycosis. An echogenic, highly cellular exudate fills the subretinal space (*) underlying a total retinal detachment in this patient and indicates a very poor prognosis for restoration of vision in the affected eye.
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2.18 Imaging findings in optic neuritis. Transcorneal ultrasonogram showing the enlarged optic nerve (ON) as a tortuous, hypoechoic band, with swelling of the echogenic optic nerve head (arrowed) seen against the anechoic vitreous in a Cavalier King Charles Spaniel. Sagittal oblique post-contrast T1-weighted MR image aligned to the orbit in a Lhaso Apso. The optic nerve is thickened and shows an increased degree of contrast enhancement. CSF samples from both dogs suggested a probable diagnosis of granulomatous meningoencephalitis.
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2.19 A sagittal oblique, fat-suppressed, post-contrast T1-weighted MR image of an optic nerve meningioma in an 8-year-old crossbred dog. A large mass (M) with tapering margins surrounds the optic nerve (ON), displacing the extraocular muscles peripherally and compressing and indenting the posterior globe (arrowed). The mass is hyperintense and therefore more contrast enhancing than the adjacent optic nerve.
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2.20 A retrobulbar abscess in a 10-year-old Border Terrier bitch. Ultrasonogram showing a complex cavitated mass (Ab) medial to the globe, compressing and displacing it (arrowed). Dorsal, fat-suppressed, post-contrast T1-weighted MR image showing a large, hypointense cavity (Ab) with surrounding contrast-enhancing tissue, located medial to the globe and severely deforming it (arrowed).
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2.21 Orbital foreign body (stick) in a 7-year-old Golden Retriever. Transcorneal ultrasonogram showing the tip of the stick as a curvilinear echogenic structure with distal acoustic shadowing (arrowed). The adjacent globe wall is distorted. Although the presence of a retrobulbar foreign body is confirmed, its precise dimensions and orientation are unclear. Sagittal STIR image showing the extent of the foreign body, which was >5 cm in length. Surrounding soft tissue inflammation is also evident in this fat-suppressed image. The size of the foreign body was grossly underestimated on ultrasonography.
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2.22 Orbital neoplasia. DV radiograph of a 13-year-old crossbred dog with exophthalmos. There is diffuse opacification of the adjacent part of the nasal cavity and frontal sinus (arrowed), which suggests a neoplasm eroding through the medial orbital wall. Transverse T2-weighted MR image of the head of a 9-year-old Staffordshire Bull Terrier with exophthalmos. The globe is displaced by a homogeneous soft tissue mass which fills the orbit, contacting, but not eroding, its bony margins. The mass appears to be confined to the orbit and the nasal cavity and frontal sinus are unaffected. CT image (soft tissue window) of the head of a 9-year-old Belgian Shepherd Dog with left-sided epistaxis, reverse sneezing and mild exophthalmos. A soft tissue mass is present in the nasal cavity, which has eroded through the medial wall of the orbit and displaced the normal orbital soft tissues. The final diagnosis was nasal carcinoma. (c, Courtesy of S Boroffka)
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2.23 Myxosarcoma in a 14-year-old crossbred dog with severe but non-painful exophthalmos. Ultrasonogram showing a hypoechoic cavity in the lateral aspect of the orbit, which measured >9 cm x 15 cm in this orientation. Sagittal T2-weighted MR image showing the complex nature of the cystic structure, which extends caudally to the temporomandibular joint.
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2.24 Parasagittal, fat-suppressed, post-contrast MR image in a 12-year-old crossbred dog with sphenoid bone neoplasia, bilateral blindness and mild exophthalmos. The presphenoid bone is markedly expanded and distorted, compressing the brain and obliterating the optic chiasm. The mass has expanded anteriorly into the apices of both orbits, disrupting both optic canals.
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2.25 CT findings in cases of orbital trauma. CT image (bone window) of a Labrador puppy that had suffered bite injuries. There are multiple displaced fractures affecting the right frontal bone and both right and left palatine bones. Fluid (blood) is present in the frontal sinuses and ethmoturbinate regions and there is unilateral dorsal and lateral globe displacement. 3D reconstruction of CT images (bone window) of a 6-year-old Beagle which sustained a gunshot wound to the face. An entry wound was observed in the right maxilla but the more extensive exit wound on the left side of the face is shown here. This case illustrates the utility of this technique in locating multiple bone fragments in the orbital region. (a, Courtesy of S Boroffka; b, Courtesy of C Snyder and the University of Wisconsin-Madison Diagnostic Imaging Service)
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2.26 Frontal bone thickening due to osteomyelitis in a 6-month-old Jack Russell Terrier with frontal area swelling and ventral deviation of the globe. Rostrocaudal radiograph of the frontal area. The affected frontal bone is thickened laterally and a smooth mass of mineralized tissue protrudes into the orbit (arrowed). Transverse T2-weighted MR image showing ventral strabismus due to thickening of the outer surface of the frontal bone. The tissue is of low signal due to mineralization. There is hyperintense fluid in the ipsilateral frontal sinus (sinusitis).
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2.27 Combined OCT images demonstrating <5 μm resolution of the fine structural detail of the retinal layers, choroid and optic nerve head (ONH) in a normal cat, which approaches ‘histopathology’. NSR = neurosensory retina; RPE = retinal pigment epithelium.

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