Page 90 - Feline diagnostic imaging

6.2 ­iseases oo the Feline rain 87

(a) (b) (c)

Figure 6.11 A 13-year-old Siamese presented for dull mentation and mass on his head above the left eye. (a) Dorsal CT image. There
is a large contrast-enhancing soft tissue mass overlying the left side of the calvarium with marked bone destruction. (b,c) Transverse
images. Invasion into the calvarium is apparent (arrows). Biopsy results were consistent with a soft tissue sarcoma. Source: Images
courtesy of Dr Merrilee Holland, Auburn University.

practices are using both modalities. The appearance of all cats [45]. The MRI appearance of a toxoplasma granu-
the extracranial tumor will obviously depend on the loma is described as being similar to a meningioma [46].
tumor type and/or the tissue of origin. Multifocal indistinctly marginated lesions are also
described for toxoplasma encephalitis (Figure 6.13) [43].
Central nervous system (CNS) mycotic infections can
6.2.2 Infection
affect outdoor as well as indoor feline patients, and
Infection is the most frequent cause of meningoencepha- most commonly include Cryptococcus, Aspergillus, and
litis in cats. It accounts for approximately one‐third of all Blastomycosis species, depending on geographic region
disease in cats with neurologic disorders [21]. There are [47]. Cryptococcus encephalitis, arising from infection with
numerous types of infectious agents to consider for C. neoformans or less commonly C. gattii, is more com-
intracranial disease, such as viral, protozoal, mycotic, monly identified in feline than canine patients. The lesions
parasitic, and bacterial. In one study, feline infectious may be intra‐ or extraaxial, and solitary or multifocal
peritonitis (FIP) and nonspecific (meningo)encepha- [46,48,49]. The lesion(s) are most commonly hyperintense
litides respectively accounted for approximately 51% and on T2W and hypointense on T1W with peripheral enhance-
36% of cases [42]. ment patterns (Figure 6.14) [48]. The rim enhancement
In case studies, FIP, due to coronavirus infection, is the represents a pseudocyst formation of this disease.
mostly frequently encountered infectious process causing Intracranial meningeal enhancement is seen in dogs but is
feline encephalopathy [21,43]. These cats tended to be not reported in cats.
younger than other cats in a study on feline meningoen- Intracranial parasitism in the form of Cuterebra species
cephalitis. This disease has a rather classic MR appearance, is seen in young outdoor cats and is the result of aberrant
characterized by ventriculomegaly, periventricular high larval migration that causes an ischemic encephalopathy
signal intensity in T2W images representing edema or cel- [50,51]. Summer is the most common time for presenta-
lular infiltrate and varying degrees of bilaterally symmetric tion. The larvae gain access via the cribriform plate.
meningeal and/or ependymal enhancement (Figure 6.12) Interestingly, the larva is uncommonly identified in
[31,43,44]. However, there have been cases in which no postmortem specimens [52]. With CT, mottling of the
macroscopic lesions have been identified [42,43]. parenchyma has been described with this infection.
Toxoplasma granulomas are relatively commonly Cuterebra encephalitis appearance on MRI is consistent
encountered in feline patients infected with Toxoplasma with vascular compromise. Typically, an area of forebrain
gondii, with central nervous system involvement (often parenchymal hyperintensity is present in T2W images and
with ocular involvement) occurring following reactivation postcontrast areas of presumed necrosis can be seen in
of latent bradyzoites [42]. If clinically affected with toxo- more severe cases. Occasionally, a track‐like focus is detect-
plasmosis, central nervous system involvement occurs in able in the T1W postcontrast images (Figure 6.15). In the