Page 681 - Withrow and MacEwen's Small Animal Clinical Oncology, 6th Edition

CHAPTER 31 Tumors of the Nervous System 659

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D E F

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• Fig. 31.1 MRI and pathologic phenotypes of canine brain tumors causing multifocal intracranial clinical
signs. (A) MRI of a cerebral meningioma with marked perilesional edema and transtentorial (arrow) and
foramen magnum herniations (arrowhead). (B) MRI (left) and gross specimen (right) of primitive neuroec-
todermal tumor causing mass effect in both cerebral hemispheres and obliterating the lateral and third
ventricles. (C) MRI of multiple meningiomas. A dural tail sign (arrow) can be seen associated with parasel-
lar mass. (D) MRI (left) and gross specimen (right) of multifocal metastatic hemangiosarcoma. (E) MRI of
butterfly glioblastoma demonstrating bilaterally symmetric wing-like tumor extensions into both cerebral
hemispheres. (F) MRI of a choroid plexus carcinoma resulting in obstructive hydrocephalus, fourth ven-
tricular dilatation, and syringohydromyelia.

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hydrocephalus, and intracranial hemorrhage. In early stages of of tumor involving the frontal lobe, falcine or subtentorial
tumor growth, compensatory autoregulatory mechanisms, such brain herniations, and marked contrast enhancement of the
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as decreased cerebrospinal fluid (CSF) production and shifting tumor. In cats, the overall incidence of tumor-associated epi-
of CSF into the spinal subarachnoid space, are effective at main- lepsy is lower than dogs, with approximately 25% of cats with
taining the intracranial pressure within physiologic ranges. For brain tumors experiencing seizures. 3,24,29 In one study, seizures
some slow-growing tumor types, such as meningiomas, intracra- were more common in cats with glioma (27%) and lymphoma
nial pressure–volume homeostatic regulatory mechanisms can (26%) than meningioma (15%). Behavioral changes are the
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remain surprisingly intact despite large tumor volumes associated most frequently reported clinical sign associated with feline brain
with significant mass effect; however, with progressive increases in tumors, being observed in 16% to 67% of cats. 3,29 Central ves-
tumor volume, autoregulatory mechanisms become overwhelmed tibular dysfunction is the most common clinical manifestation
and intracranial hypertension (ICH) develops. ICH, and the of brain tumors affecting the brainstem. 26,30 Nonspecific com-
resulting detrimental decrease in cerebral perfusion pressure, is plaints (e.g., lethargy, inappetance) were identified in more than
the common pathophysiologic denominator underlying many of 20% of cats with brain tumors and are frequently reported in
the primary and secondary mechanisms of tumor-associated brain dogs with pituitary tumors. 3,31
injury. Acute clinical deterioration observed in animals with brain Tumors involving forebrain structures are more common than
tumors and ICH is often the result of vasogenic or interstitial (i.e., those in the brainstem. 1–3,30 In many cases with solitary masses,
obstructive hydrocephalus) brain edema, abnormalities of cerebral observed neurologic deficits are reflective of the focal neuroana-
blood flow (ischemia or hemorrhage), brain herniations, or com- tomic area involved. However, dogs and cats may present with
binations of these mechanisms (Figs. 31.1A, B). 25 neurologic deficits indicative of multifocal intracranial disease
A brain tumor should be considered as a differential diag- (see Fig. 31.1).
nosis in any middle-aged or older animal with a clinical history In 50% of dogs with solitary PBTs, multifocal signs result from
consistent with peracute, acute, or chronic brain dysfunction, the tumor or its secondary effects involving multiple region of
especially if clinical signs are progressive. In dogs, seizures are the brains. The phenotype of some PBTs, such as butterfly glio-
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the most common clinical manifestation of intracranial neo- blastomas, by definition requires tumor invasion of both cerebral
plasia and occur in approximately 50% of dogs with forebrain hemispheres. Multiple tumors may also be present, which occurs
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tumors. 2,26–28 The index of suspicion for a brain tumor should occasionally in canine meningiomas, but is seen in approximately
increase in dogs that experience a new onset of seizure activity 20% of cats with meningiomas. 3,33,34 Canine oligodendrogliomas
after 5 years of age, especially in at-risk breeds. Significant risk can manifest with multifocal or diffuse leptomeningeal involve-
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factors for tumor-associated structural epilepsy based on mag- ment. Rare case reports describing synchronous PBTs of dif-
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netic resonance imaging (MRI) diagnosis include the presence ferent histologies and synchronous PBTs and SBTs also exist.