Computed tomographic and otoscopic findings in canine otitis externa

Introduction / Purpose: Otitis externa (OE) is a common condition in dogs. Computed tomography (CT) and otoscopy are commonly used in the diagnostic work-up of canine ear conditions, and can demonstrate different pathological aspects of the external ear canal. Although both modalities are commonly used in conjunction, there is little information about how CT findings correlate with otoscopic examination. The purpose of this study is to establish this, particularly regarding the sensitivity of CT for OE. Methods: Head CT studies of dogs with otoscopically confirmed OE were blindly reviewed by two observers. CT features assessed were wall mineralisation, thickness, and contrast enhancement. CT findings were determined by consensus and compared with otoscopic findings, performed by a board-certified dermatologist. We hypothesize that CT will be a sensitive modality for diagnosing OE.
Results:Twenty-four dogs were included. The sensitivity of CT for diagnosing OE was 100% (41/41 ears, 95% confidence interval [CI]: 91.4-100%), and the CT-derived diagnosis of OE (uni- or bilateral) matched the otoscopic diagnosis in 20/24 cases (83.3%, 95% CI: 62.6-98.3%; κ = 0.52). CT was sensitive for identifying ear canal stenosis (92.3%, 95% CI: 79.7-97.4%). However, only three of seven ears without otoscopic signs of OE were classified as unaffected on CT. Interestingly, four out of five cases of acute OE had ear canal mineralisation, in contrast to 12/19 (63.2%) chronic cases. Discussion / Conclusion: CT is a sensitive diagnostic technique adjunct to otoscopic examination for canine OE. Ear canal wall mineralization does not necessarily imply the presence of chronic OE.