A Comparison of Radiography Versus Computed Tomography in the Diagnosis of Middle Ear Disease in the Dog

The purpose of this study was to compare CT and radiography for diagnosing the presence and severity of middle ear disease in dogs with chronic otitis externa. Thirty-one dogs that were presented for a total ear canal ablation and bulla osteotomy were recruited. Three normal dogs served as controls. All dogs were examined using radiography and CT. Three radiologists independently evaluated imaging studies in random order. A visual analog scale method was used for scoring certainty and severity of middle ear disease. Surgical findings were recorded intra-operatively. Bulla lining samples were submitted for histopathology and scored by a single pathologist who also used a visual analog scale system. Findings from both modalities agreed more closely with surgical findings than with histopathology findings. With either surgery or histopathology as the gold standard, CT was more sensitive than and as specific as radiographs for predicting presence and severity of middle ear disease. Overall severity of middle ear disease was lower in the right versus the left ears. For CT, inter-observer variance of middle ear certainty was 217.04 while radiographic variance was 126.14 on the side with lower severity estimates. Both radiography and CT were more accurate for predicting the severity of the disease than its presence. Findings indicate that CT is more accurate and reliable than radiography in diagnosing middle ear disease for dogs with chronic otitis externa, but only when severity of disease is moderate or high. With low severity of disease, reader diagnostic certainty for both modalities becomes more variable.