Early Signs in the Ear: Dorsal Contrast Enhancement Flags Feline Otitis Media

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

Joo-Young Lee, Jihye Choi, Seung-Jo Park, Jin-Woo Jung, Munsu Yun, Seonghyeon Baek, Kija Lee, Sang-Kwon Lee

Background
Otitis media in cats often arises from upper respiratory infections and may be asymptomatic in early stages. While tympanic bulla effusion is a recognized imaging marker, contrast enhancement (CE) patterns on CT or MRI have not been well studied. This multicenter retrospective study aimed to assess the prevalence and types of tympanic bulla CE in relation to the presence and severity of bulla effusion in cats, with a focus on identifying early imaging markers of otitis media.

Methods
CT or MRI scans of 322 cats (644 tympanic bullae) performed between 2011 and 2024 at six veterinary institutions were retrospectively reviewed. Effusion severity and CE patterns were graded by standardized criteria. Cases with masses or suspected primary middle ear neoplasia were excluded. Associations between CE patterns, effusion presence and severity, and clinical signs were statistically analyzed.

Results
Bulla effusion was present in 105 bullae (16.3%), and CE was significantly more common in effused bullae (64.8%) than in non-effused bullae (1.0%) (p < .001). CE prevalence increased with effusion severity: 20% in mild, 62.5% in moderate, and 73.2% in severe effusions. Focal dorsal rim enhancement was the most common pattern (observed in all mild and moderate cases with CE), whereas additional patterns (complete rim, ventral/lateral rim, internal heterogeneous enhancement) were found only in severe cases. Dorsal CE was observed in a few non-effused bullae, potentially representing very early or subclinical disease.

Limitations
Histopathologic correlation was not available, and follow-up imaging was not performed to track disease progression. Imaging protocols varied across institutions, and the study population included relatively few mild/moderate effusion cases. These factors may have influenced detection sensitivity and statistical power. Pseudoenhancement in CT and intermodality differences (MRI vs. CT) also present interpretation challenges.

Conclusions
Focal dorsal enhancement of the tympanic bulla is the earliest and most frequent CE pattern in cats with bulla effusion, supporting its potential as an early imaging marker of otitis media. The progression of CE patterns parallels effusion severity and may help distinguish early subclinical from more advanced disease. Recognizing this imaging sign may enhance diagnosis and intervention in feline middle ear disease.

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