Computed tomography shows limited accuracy in differentiating histological types of canine ear canal masses

Objective To describe the epidemiological characteristics and CT features in dogs with external ear canal (EEC) masses and assess the ability of CT to predict histopathological diagnosis. Methods This was a retrospective, single-center study including 70 dogs that underwent otoendoscopic examination, head CT imaging, and histopathological analysis. Masses were categorized into 5 groups according to histopathological diagnosis. Computed tomography images were reviewed, and features were compared between groups. Results 71 EEC masses were studied, including inflammatory polyps (31 of 71 [44%]), malignant tumors (17 of 71 [24%]), inflammatory masses in a context of chronic otitis externa (15 of 71 [21%]), benign tumors (4 of 71 [6%]), and unclassified masses (4 of 71 [6%]). French Bulldogs were overrepresented (26 of 70 [37%]) and mainly affected by inflammatory masses (22 of 26 [85%]). Fifty-nine of 71 masses (83%) visualized on otoendoscopy were delineated on CT. Partial or total obliteration of the ipsilateral tympanic bulla by soft tissue–attenuating material was noticed in 53 of 71 dogs (75%). An enhancing pedicle at the medial aspect of the masses was only seen in the polyp group (11 of 31 [35%]), and 9 of 11 pedicles were mineralized. No other CT variable allowed differentiation between histopathological groups. Conclusions CT delineates EEC masses with a moderate sensitivity and shows a limited ability to predict histopathological diagnosis. Clinical Relevance A variably mineralized enhancing pedicle at the medial aspect of an EEC mass is strongly suggestive of an inflammatory polyp.