Adenocarcinoma of the middle ear with osteolysis of the tympanic bulla in a cat.

Peripheral vestibular disease and lethargy were attributed to an adenocarcinoma in the middle ear of a 10-year-old cat. The tumor was invasive, inducing severe lysis of the tympanic bulla and adjacent temporal bone. Direct invasion to the meninges and brainstem also was observed. Neoplasms of the middle ear are rare in cats, with squamous cell carcinomas reported most commonly, but should be considered as causes of chronic otitis or signs of peripheral vestibular disease.