Page 276 - Atlas of Small Animal CT and MRI

266 Atlas of Small Animal CT and MRI

nerve branches (Figure 2.10.9). Marked unilateral Cavernous sinus syndrome
temporalis and masseter muscle atrophy is most often
also present. On MR images, the affected muscle is T1 The cavernous sinuses are located on either side of the
and T2 hyperintense, because of fatty infiltration from sella turcica and contain the internal carotid arteries
denervation, and mildly to moderately contrast enhances. and their associated sympathetic plexuses; the third,
fourth, and sixth cranial nerves; and branches of the fifth
Lymphoma cranial nerve. Mass lesions that encroach on or invade the
Lymphoma can occasionally involve the cranial nerves, cavernous sinuses will therefore often cause a cranial poly-
either locally or as part of a more widespread central neuropathy with clinical signs referable to the functions of
nervous system or systemic distribution. One or more these cranial nerves. Both neoplastic and inflammatory
cranial nerves can be affected, and nerve involvement causes have been reported. Imaging features will depend
is often bilateral. Affected nerves are generally enlarged on the inciting lesion but often include the presence of a
and T1 iso‐ to hypointense and T2 iso‐ to hyperintense. space‐occupying mass within or near the pituitary fossa
Uniform moderate to marked enhancement is seen fol- with evidence of invasion or compression of the sinuses
lowing contrast administration (Figures 2.10.10, 2.10.11). (Figure 2.10.12). 13–15

Figure 2.10.1 Normal Cranial Nerve II (Canine) CT & MR

(a) CT, OP (b) CT+C, OP (c) T1+C FS, DP
The normal optic nerve (a,b: white arrowhead) can usually be identified on CT images from the optic canal (a,b: black arrowhead) to the
optic disc (a,b: arrow). The normal optic nerve can also be seen on MR images (c: arrowhead). Because the nerve takes a tortuous path
through the retrobulbar space, it is usually not possible to see the entire length of the extracranial part of the nerve on a single image.

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