Ear Canal Mass in a Dog? CT Can’t Tell Type—Except When You See the Pedicle

Computed Tomography Shows Limited Accuracy in Differentiating Histological Types of Canine Ear Canal Masses

Philippe Colombe; Yannick Ruel; Pascal Prélaud; Amaury Briand; Mélanie Moreira André; Albert Agoulon; Frédérique Degorce-Rubiales; Hugues Gaillot

Background

External ear canal (EEC) mass-like lesions in dogs encompass inflammatory polyps, inflammatory hyperplastic lesions, and neoplasms (benign and malignant). Computed tomography (CT) is frequently used to assess extent, but its ability to predict histopathological diagnosis had not been systematically evaluated. This study characterized CT features of EEC masses and tested whether CT can differentiate histologic categories.

Methods

Retrospective, single-center study of 70 dogs (71 EEC masses) seen 2011–2022 at a referral hospital. Inclusion required otoendoscopic identification of an EEC mass, same-day head CT, and histopathology within 1 month (via otoscopy-guided sampling or surgery). Three readers (two board-certified radiologists and a resident) reviewed anonymized CTs using predefined qualitative and quantitative grids; consensus readings were recorded. Masses were grouped as inflammatory polyps, inflammatory masses (chronic otitis context), benign tumors, malignant tumors, or unclassified. Statistical testing compared CT variables across groups, and optimal cut-points were explored.

Results

Seventy-one masses were classified as inflammatory polyps 31/71 (44%), malignant tumors 17/71 (24%), inflammatory masses 15/71 (21%), benign tumors 4/71 (6%), and unclassified 4/71 (6%). French Bulldogs were overrepresented (26/70, 37%) and predominantly had inflammatory lesions (22/26, 85%). CT delineated 59/71 (83%) masses seen on otoscopy; 12/71 (17%) were not recognized as a discrete mass on CT. Ipsilateral tympanic bulla (TB) soft tissue content occurred in 53/71 (75%). An enhancing pedicle at the medial aspect of the mass was observed only with inflammatory polyps (11/31, 35%), and most pedicles were mineralized (9/11). No other CT variable reliably distinguished groups. Retropharyngeal lymph node width ratio was higher in malignant tumors than polyps (optimal cut-point 1.12; accuracy 69%, sensitivity 88%, specificity 58%), but overlap limited clinical utility. Features suggesting local aggressiveness (eg, temporal bone lysis, intracranial enhancement) were infrequent overall.

Limitations

Group sizes—especially benign tumors and unclassified lesions—were small, reducing statistical power; multiple variable testing raises type I/II error risks. Histopathologic classification has inherent challenges (eg, metaplasia potentially obscuring polyp origin; adenoma vs well-differentiated carcinoma distinctions). Lymph node cytology/histology was not available to confirm metastatic status. Retrospective design limited standardization of sampling and reporting.

Conclusions

CT detects most EEC masses and frequently reveals concurrent middle ear involvement, but it has limited accuracy for predicting histopathological type. A variably mineralized, enhancing medial pedicle is a useful CT sign that strongly suggests an inflammatory polyp; otherwise, CT features largely overlap among inflammatory and neoplastic categories. Given the 24% prevalence of malignant tumors in this cohort and CT’s limited specificity, biopsy with histopathology is recommended for any canine EEC mass, and systematic evaluation of the tympanic bulla should be included in imaging workups.

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