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.