Focal Dorsal Enhancement of the Tympanic Bulla: An Early Indicator in Feline Otitis Media.

Evaluating the morphological changes of the tympanic bulla and the contrast enhancement (CE) patterns are key factors in diagnosing otitis media and predicting its underlying etiology. However, limited research exists on the CE patterns of the tympanic bulla in cats with bulla effusion. This retrospective study aimed to investigate the prevalence and patterns of CE in the tympanic bulla based on the presence and severity of bulla effusion in cats. Feline head CT or brain MRI images from six institutions were analyzed. Transverse pre- and postcontrast CT and MRI images were reviewed to assess the presence and severity of bulla effusion, along with the presence, pattern, and location of tympanic bulla CE. A total of 644 tympanic bullae from 322 cats were included. Bulla effusion was detected in 105 of 644 bullae, while CE was observed in 73 of 644 bullae: 5 of 539 bullae without effusion and 68 of 105 bullae with effusion. CE was significantly more common in cats with bulla effusion, with the incidence increasing as effusion severity progressed. Focal rim enhancement, predominantly localized to the dorsal aspect of the tympanic bulla, was the most frequent enhancement pattern. In cases with mild or moderate bulla effusion, only focal dorsal enhancement was observed. However, in cats with severe bulla effusion, additional patterns, including focal ventral or lateral, complete rim, and internal enhancement, emerged. These findings suggest that both the incidence and patterns of CE evolve with the progression of bulla effusion in cats and that focal dorsal enhancement may be an early indicator.