Computed Tomographic Findings in Canine Otitis Externa

Otitis externa (OE) is a common condition in dogs. Otoscopic examination is the standard diagnostic procedure, but not all external ear canal structures can be assessed otoscopically. Computed tomography (CT) has become a gold standard in the assessment of middle ear disease. This study aimed to assess the validity of CT for canine OE and to compare CT-specific and otoscopy-specific findings that are consistent with OE. CT studies of dogs referred for suspected OE were blindly reviewed by three observers for ear canal wall mineralization, thickness, and contrast enhancement. Otoscopic findings were used as the reference standard. The sensitivity and specificity of CT for the diagnosis of OE were 98.2% (95% confidence interval [CI]: 90.4%-99.7%) and 60.0% (95% CI: 10.7%-76.6%), respectively. The positive predictive value (PPV) was 84.4%, and there was substantial agreement (weighted κ = 0.65) between CT and otoscopic diagnosis of OE. There was moderate agreement (weighted κ = 0.47) between the presence of CT ear canal wall contrast enhancement and the degree of erythema otoscopically, and moderate agreement (weighted κ = 0.58), comparing the consensus CT grade for ear canal wall thickness to the grade of ear canal stenosis on otoscopic examination. The presence of external ear canal wall mineralization on CT was independent of disease (p = 0.49) and disease duration (p = 0.26), indicating mineralization of the external ear canal wall on CT is not necessarily related to chronic OE. There is substantial agreement between CT and otoscopy, supporting its use as a diagnostic technique for OE.