The Continuum of Eustachian Tube Obstruction in Cats: A temporal bone study

The Eustachian tube is a canal from the tympanic cavity to the nasopharynx that is responsible for the aeration, drainage, and pressure equalization of the middle ear. Partial or complete blockage of the tube can trigger severe ear disease. We evaluated pathologic changes from Eustachian tube obstruction (ETO) in 15 temporal bones from cats with bilateral ETO from the temporal bone collection at the University of Minnesota Medical School Otopathology Laboratory. The samples were evaluated for histopathological changes to investigate the continuum of the disease at intervals of 2 days, 1-week, 2-weeks and 4-weeks. Temporal bones were sectioned in the horizontal plane and every 10^th section was stained with hematoxylin and eosin. One section from each ear was stained with periodic acid-Schiff and Alcian blue. Sections were studied under light microscopy. The results revealed moderate hyperplasia equally developed throughout the epithelial layer surrounding the middle ear and neutrophil-rich inflammatory cell infiltration. As the duration of obstruction prolonged to the 4^th week, compositional change of the middle ear effusion from serous to mucoid that was accompanied with granulation tissue formation was observed. In conclusion, the severity of the findings related to ETO are directly proportional to the duration of the disease. Therefore, patients presenting with long-lasting complaints of ear diseases should be examined for dysfunction or blockage of the Eustachian tube.