Page 207 - Atlas of Small Animal CT and MRI

2.6

Noninfectious inflammatory disorders

Although a number of noninfectious inflammatory contrast enhancement characteristics as described
disorders of the brain of the dog and cat have been for CT (Figures 2.6.1, 2.6.2). 1,3,5
reported, two entities, granulomatous meningoencepha- Meningeal involvement is documented in many
litis and necrotizing encephalitis, are the most common patients with GME, and abnormal imaging findings are
and best described. Necrotizing encephalitis can be sometimes limited to prominent meningeal enhance-
1
further subdivided into necrotizing meningoencephali- ment (Figure 2.6.1). In a minority of patients, imaging
tis and necrotizing leukoencephalitis, and it is possible may be normal or lesions may not contrast enhance. 1,5
that these represent different manifestations of the same
disease. All three of these conditions are thought to be Necrotizing encephalitis
autoimmune disorders.
Necrotizing meningoencephalitis

Granulomatous meningoencephalitis Necrotizing meningoencephalitis, sometimes referred to
as Pug dog encephalitis, is a nonsuppurative, necrotiz-
Granulomatous meningoencephalitis (GME) is an ing, inflammatory brain disorder. Small‐ and toy‐breed
8
idiopathic inflammatory disorder of the central nervous dogs are predisposed, and Pug, Maltese, and Chihuahua
system, characterized by perivascular mononuclear cell breeds are highly overrepresented. Median age of onset
infiltrates. Young to middle‐aged (4–5 years), female, is 1.5–3 years, and females are affected more commonly
2
small‐ and toy‐breed dogs are predisposed, while the than males. Lesions may be focal or asymmetrically
disorder is less common in large‐breed dogs and rare multifocal and involve both gray and white matter of
in cats. Lesion distribution may be focal, disseminated the cerebral hemispheres and overlying meninges. 1,8–10
(multifocal), or ocular, with the focal and disseminated Cerebellar and brainstem involvement, though uncom-
forms predominating. Lesions primarily involve white mon, has been reported. Grossly, lesions are frequently
11
matter, but gray matter and meninges may also be cavitary and associated with significant brain swelling
affected. This disorder most often affects the forebrain, from inflammation and edema. 8
brainstem, or spinal cord, with the cerebellum and optic Lesions may be hypoattenuating on unenhanced
nerves less frequently involved. 1–7 CT images when cavitary or when associated with sig-
Depending on the extent of associated edema, nificant brain edema. Edema may also induce midline
lesions may have ill‐defined hypoattenuation on shift, brain herniation, and other features of mass effect.
unenhanced CT images and will variably contrast Contrast enhancement is variable on CT, ranging from
enhance. Enhancement can be absent, heterogeneous absent to moderate, but when present, the enhance-
and ill-defined, or may sometimes reveal a well‐ ment pattern is heterogeneous and margins may be
delineated mass. Lesions are typically T1 iso‐ to poorly delineated. On MR images, lesions are T1 iso‐ or
hypointense and T2 hyperintense and have similar hypointense and T2 hyperintense, involve the cerebral

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.
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