Computed tomographic findings in the canine external ear canal and their associations with duration of otitis externa.

Introduction / Purpose: Computed tomography (CT) is commonly used in suspected canine otitis externa (OE) and media. Ear canal wall mineralisation is thought to be associated with chronic otitis externa. Contrast enhancement is used in other organs as a marker of inflammation. The aim of this study was to establish whether external ear canal mineralisation and contrast enhancement were associated with duration of canine otitis externa.
Methods: Two observers blindly reviewed head-CT studies in a cohort of dogs to assess external ear wall mineralisation and contrast enhancement. Ears were classified by otoscopic examination as disease-free or diseased (OE), with diseased subdivided into acute (≤ 4 weeks) and chronic (> 4 weeks). We hypothesized that disease duration and external canal mineralisation were not associated, and that external ear canal wall contrast enhancement was associated with OE.
Results: Forty dogs were included in the study. The presence of external ear canal mineralisation on CT was independent of disease duration (p=0.49), with mineralisation in 80% (20/25) of disease-free, 77.8% (35/45) of chronic and 80% (8/10) of acute OE. The presence of external ear canal wall contrast enhancement was dependent on disease (p<0.001). with significant enhancement in chronic OE compared to disease-free (p <0.001).
Discussion / Conclusion: Mineralisation of the canine external ear canal wall on CT is not necessarily related to chronic otitis externa, a degenerative process should also be considered. CT contrast enhancement of the external ear canal can be used as an indicator for active canine otitis externa in chronic, but not acute cases.