Comparative performance of video-otoscopy and CT in the diagnosis of external ear disease in cats

The aim of the study was to compare CT with video-otoscopy for detecting external ear canal masses in cats and to describe CT features of feline external ear disease.

This retrospective study evaluated the external ear canals of cats that underwent both CT and video-otoscopy. Two blinded observers reviewed the CT scans and their findings were compared with video-otoscopy results evaluated by one blinded observer.

Of the 32 examined ears, 13 had an external ear canal mass detected by both CT and video-otoscopy. No false positives were identified. All 19 ears without masses were correctly identified as true negatives, resulting in perfect agreement for mass detection (kappa = 1.000). On histopathology, 9/13 masses were diagnosed as polyps, 1/13 masses was diagnosed as carcinoma, 2/13 did not undergo histopathology and 1/13 masses seen on video-otoscopy was diagnosed as otitis externa with granulomatous tissue formation. Of the 16 cats examined, 12 had a mass in the external ear canal diagnosed by video-otoscopy: six domestic shorthairs, five Maine Coons and one Oriental Shorthair cat. Of these cats, 11 had a unilateral mass and one had a bilateral mass. There was very low agreement between CT and video-otoscopy for ear canal wall enhancement and erythema (kappa = 0.033), as well as for ear canal thickening and stenosis (weighted kappa = 0.056). There was no significant difference between chronic and non-chronic clinical signs in terms of the presence of ear canal wall mineralisation (P = 0.223).

There is high agreement between video-otoscopy and CT in detecting external ear canal masses in cats. However, there is very low agreement between CT and video-otoscopy for ear canal wall enhancement, erythema, thickening and stenosis. The presence of external ear canal mineralisation did not correlate with the chronicity of clinical signs.