Page 833 - Problem-Based Feline Medicine

37 – THE CAT WITH STUPOR OR COMA 825

Pathogenesis Hyperostosis of the skull is occasionally present on
survey radiographs of the skull, especially with menin-
Neoplasia can arise from structures within or surround-
giomas. A “sky-line” view may be necessary to image
ing the brain (primary brain tumors).
this abnormality.
Neoplasia secondarily involves the brain via metasta-
Diagnosis of a structural intracranial abnormality in the
sis or via direct extension from extraneural sites.
brain is most readily accomplished with magnetic res-
Primary tumors within the skull, nasal cavity or
onance (MR) imaging or computed tomography
frontal sinuses can extend directly into the brain.
(CT) of the brain.
Meningioma is the most common brain tumor in ● A broad-based, extra-axial (arising outside and push-
cats. Meningiomas arise from the arachnoid layer of the ing into the parenchyma) contrast-enhancing mass
meninges. Meningiomas are usually histologically on CT or MR imaging is found in most instances of
benign, but occasionally are malignant. meningioma.
● The CT and MR appearance of gliomas is varied
Some younger cats with mucopolysaccharidosis have
and enhancement after contrast administration may
a high incidence of meningiomas.
not be present. As these tumors arise from brain
Gliomas arise from cells of the brain parenchyma. parenchymal cells, they are found within the neu-
These include astrocytes and oligdendrogliocytes. roaxis (intra-axial).
● Choroid plexus tumors, because of the increased
Choroid plexus tumors arise from areas where the
concentration of blood vessels within the tumor,
choroid plexus is concentrated (the lateral, third and
often enhance markedly after contrast adminis-
fourth ventricles).
tration. Because of their association with the ven-
Signs reflect either primary nervous parenchymal dam- tricular system, associated hydrocephalus is
age from the tumor, or secondary pathophysiological common.
sequelae such as hemorrhage and edema. Frequently,
Cerebrospinal fluid often contains elevations in pro-
these secondary sequelae are more devastating to
tein content but this finding is not pathognomonic for
intracranial function than the primary disease itself.
brain tumors.
● Cerebrospinal fluid can contain evidence of
inflammation (contains elevations in nucleated
Clinical signs
cells and protein content). If CSF is the only assess-
Middle-aged to older cats are most commonly ment made, an erroneous diagnosis of encephalitis
affected. Cats are usually older than 5 years of age with may be made.
a median age of onset of clinical signs at 9 years of age. ● Cerebrospinal fluid collection may be associated
with an increased mortality in cats with space-
Clinical signs are often slowly progressive, however,
occupying mass lesions within the intracranial
they can also occasionally begin acutely and be rapidly
space, because of the sudden decrease in pressure at
progressive.
the cisterna magna.
Signs reflect the intracranial location of the lesion.
● Signs include seizures, circling, blindness, behavior Differential diagnosis
changes, cranial nerve abnormalities, and may
Cats with intracranial tumors may present with signs
progress to stupor and coma.
similar to other intracranial diseases.
● If the brain stem is involved, head tilt, nystagmus
and paresis are most common. There are no pathognomonic clinical signs for intracra-
nial tumor.
Congenital hydrocephalus may be associated with
Diagnosis
changes in the skull (“Dome-shaped” skull, persistent
Routine laboratory evaluations (CBC, biochemistry fontanelle), but these will not be present with acquired
profile) are not affected by intracranial neoplasia. hydrocephalus.