Histologic characterization of the cat middle ear: in sickness and in health.

The purpose of this study was to establish microscopic normal in the middle ear of the cat while concurrently characterizing gross and microscopic lesions reflecting spontaneous otitis media. Both ears from 50 cats were examined grossly and processed for histologic examination of the external, middle, and internal ear on a single slide. Gross lesions of the middle ear were present in 14 of 100 (14%) and included turbid fluid, frank pus, hemorrhage, and fibrous thickening of the auricular mucoperiosteum. Histologically, 48 of 100 (48%) ears had evidence of ongoing or previous inflammatory middle ear disease, including proteinaceous fluid; vascular ectasia; expansion of the auricular mucoperiosteum by neutrophils, lymphocytes, and macrophages; cholesterol clefts; hemorrhage; fibrin; granulation tissue; membranous pseudo-glands; fibrosis; proliferation and/or osteolysis of the tympanic and septum bullae. Histologic lesions were identified in 34 of 100 ears (34%) lacking gross evidence of disease. Ears were classified histologically as either normal (52/100 [52%]) or diseased (48/100 [48%]). Diseased ears were further classified as mild to moderate (37/100 [37%]) or severely (11/100 [11%]) affected. Internal ear involvement was present in 11 of 100 (11%) ears. Histologic evidence of middle ear disease in cats is far greater than gross lesions or clinical literature suggests; further investigation and correlation of clinical and histologic disease are warranted. With minimal additional preparation, diagnostic specimens may be readily prepared and evaluated for this integral sensing organ.