Page 96 - Atlas of Small Animal CT and MRI

1.6

Globe

Introduction of the lens and globe have been reported to be better
seen on MR than on CT images. 4
CT is often used to image the structures of the orbit and
surrounding skull (see Chapter 1.5). It can also be used Inflammatory disorders
for imaging the major structures of the globe, including
the anterior and vitreous chambers, as well as the lens Optic neuritis can be seen on MR images as hyperinten­
(Figure 1.6.1). MRI is an excellent modality to image the sity of one or both optic nerves in water­sensitive
structures of the globe and optic nerve. The cornea, imaging sequences. The nerve may be hyperintense
anterior and posterior chambers, ciliary body, lens, within the orbit and/or at the level of the optic chiasm. 5
vitreous chamber, and retina are visible on standard Granulomatous meningoencephalitis has been
sequences (Figure 1.6.2). The optic nerve can also be reported to involve the optic nerves. On MR images, it
1
evaluated and followed to the optic chiasm, both in appears as isointense regions on T1 and T2 weighted
transverse images and when dorsal or sagittal plane images, with intense contrast enhancement (see
sequences are oriented obliquely along the long axis of Chapter 2.10). 6
the nerve. The optic nerve is surrounded by cerebrospinal Anterior uveitis is defined as inflammation of the
fluid (CSF), which appears hyperintense on T2 and anterior chamber of the eye. On MR images, increased
hypointense on T1 images. Fat nullifying sequences, signal intensity can be seen on T1 images, and contrast
such as STIR, as well as thin collimation can help to enhancement may also be observed (Figure 1.6.4).
suppress the bright fat signal and allow visualization of Episcleritis involves inflammation of the tissues sur­
2
the CSF and nerve. Disorders of the optic nerve are rounding the sclera. The periocular tissues are thickened
discussed in Chapter 2.10. and T1 and T2 hyperintense and are intensely contrast
enhancing (Figure 1.6.5).
Trauma
Neoplasia
Trauma to the eye commonly presents as proptosis,
with the possibility of additional trauma to the surround­ Melanoma arising from the uvea has been described
ing bones and soft tissues of the orbit (Figure 1.6.3). on MR imaging in dogs. The mass was T1 hyperintense
Penetrating trauma to the eye is not commonly evaluated and T2 hypointense with contrast enhancement
7
with CT or MRI, but hemorrhage, inflammation, and (Figure 1.6.6). T1 hyperintensity is a property of mela­
altered anatomic structures would be expected findings. nin that has been described in other regions of the body.
Foreign bodies and associated inflammation in the sclera A case of melanoma arising from the choroid and
can be seen as a mass lesion that deforms the scleral surrounding the optic nerve was T1 and T2 hypointense.
8
shape with contrast enhancement. Traumatic ruptures On CT images, melanoma may appear hyperattenuating
3

Atlas of Small Animal CT and MRI, First Edition. Erik R. Wisner and Allison L. Zwingenberger.
© 2015 John Wiley & Sons, Inc. Published 2015 by John Wiley & Sons, Inc.
86