Abstract
Abstract

Backround
The endolymphatic sac is an organ devoid of sensory receptors. It is connected with the endolymphatic compartment and contains endolymph. Endolymphatic sac tumor is a rare neoplasm involving the middle and inner ear described in humans and dogs, does not show cellular characteristics of malignancy, but can be locally invasive
and involve destruction of the temporal bone and adjacent structures.
Case description:
An 8 months old female cat was referred because of sudden onset of vestibular
signs starting 3 days prior to referral.
On clinical examination the patient showed depression, right head-tilt, left sided
facial paralysis, horizontal nystagmus with fast phase to the left.
The magnetic resonance images showed a voluminous extra axial lesion, with
irregular morphology and well defined margins, with intracranial extension in
the region of the pons, rostral medulla oblongata, cerebellar vermis, floccule
and left cerebellar hemisphere.
Due to the progressive clinical deterioration, the cat was euthanized two weeks
later. A necropsy was then performed and histological samples taken.
The necropsy revealed the presence of a voluminous dark red irregular mass
extending from the tympanic bulla to the posterior cranial fossa following the
left glossopharyngeal nerve.
The histopathologic exam of the extra-axial lesion featured a non-encapsulated,
moderately cellular, rather loose, proliferation of cuboidal to columnar
epithelium breaching through chunks of an otherwise normal appearing dura
mater and invading some cranial nerves.
 Sections of the cerebellum and
brainstem revealed moderate, focal, impingement of the
parenchyma with very mild extension of the proliferating cells into the ventral
left side of the medulla oblongata.
 Based on these histological characteristics,
the lesion was defined as endolymphatic sac tumor, a rare neoplasm described
in human beings and with 2 reports in dogs.


Conclusion
To our knowledge, this is the first report describing an endolymphatic sac tumor
in a cat.


Key words: cat, endolymphatic sac, inner ear, labyrinth diseases, neoplasia