Page 937 - Problem-Based Feline Medicine

43 – THE CAT WITH ATAXIA WITHOUT WEAKNESS 929

Signs are usually progressive over weeks to months. mass on CT or MR imaging is found in most
instances of meningioma.
Occasionally, clinical signs begin acutely.
● The CT and MR appearance of gliomas is varied
Intention tremor is often associated with other signs and enhancement after contrast administration may
of cerebellar disease including ataxia (incoordination; not be present. As these tumors arise from brain
swaying from side to side), dysmetria (“goose-step- parenchymal cells, they are found within the neu-
ping”; overflexing of the limbs when walking), menace roaxis (intra-axial).
deficits (with normal vision and pupillary light ● Choroid plexus tumors often enhance markedly
reflexes), head tilt, and nystagmus (combination quick after contrast administration because of the
followed by slow movement of the eyes). increased concentration of blood vessels within
the tumor. Because of their association with the
Signs reflect either primary nervous parenchymal
ventricular system, associated hydrocephalus is
damage from the tumor or secondary pathophysiolog-
common.
ical sequelae such as hemorrhage and edema.
Cerebrospinal fluid often has increased protein con-
Meningiomas are the most common brain tumor in
centration but this finding is not pathognomonic for
cats and are usually histologically benign.
neoplasia.
● Less-frequent tumors arise from astrocytes, oligo-
dendrogliocytes, ependymal cells and choroid Cerebrospinal fluid may have evidence of inflamma-
plexus cells. tion (increased nucelated cells and protein content). If
● Medulloblastoma is a rare primary brain tumor that CSF is the only assessment made, encephalitis may be
involves the cerebellum. erroneously diagnosed.
● Neoplasia may also secondarily involve the brain
Skull radiographs or advanced imaging are necessary
via metastasis or via direct extension from extra-
to assess the middle and inner ear. Abnormalities seen
neural sites.
with these studies, however, are not always definitive for
Tumors involving the inner ear may damage the neoplasia, and tissue diagnosis at surgery is often nec-
peripheral vestibular system, resulting in vestibular essary to accurate assessment. Destruction (lysis) of the
ataxia, in which the cat leans, drifts, falls or rolls bone of the bulla is more often associated with neopla-
toward the side of the lesion and has a head tilt. sia as compared to inflammation.
Nystagmus may also be present. Occasionally tumors
extend through the tympanic membrane and are evident
Differential diagnosis
during otoscopic examination, but this is rare. See page
845 “The Cat With a Head Tilt, Vestibular Ataxia or Congential and inherited cerebellar diseases occur in
Nystagmus”. younger animals.
Squamous cell carcinoma and adenocarcinoma are the Cerebrovascular, traumatic and inflammatory condi-
most common tumors affecting the peripheral vestibu- tions can mimic the signs of a brain tumor.
lar system.
Treatment
Diagnosis Corticosteroids (prednisolone 1–2 mg/kg q 12 h) may
reduce peritumoral edema and improve clinical signs.
Routine laboratory data (e.g. hematology, biochem-
istry, urinalysis) are normal. Surgical removal of primary brain tumors may be
accomplished, especially with meningioma.
Diagnosis of a structural intracranial abnormality in the
brain is most readily accomplished with magnetic res- A well-encapsulated, firm whitish mass is most often
onance (MR) imaging or computed tomography encountered at surgery in cats. Cortical parenchyma is
(CT) of the brain. usually not infiltrated but rather compressed in cats,
● A broad-based, extra-axial (arising outside and leaving indentations in the nervous tissue parenchyma
pushing into the parenchyma) contrast-enhancing after resection.