Ultrasound Rivals CT for Feline Otitis Media: 97% Accuracy in New Study

Accuracy and Feasibility of Ultrasound in the Diagnosis of Otitis Media in Cats

Tim Chan, Ramon Almela, Agustina Anson

Background

Otitis media (OM) in cats involves fluid accumulation within the tympanic bulla (TB), usually confirmed via CT or MRI. However, these modalities require anesthesia, are costly, and less accessible. Ultrasound (US) may offer a rapid, low-cost, minimally invasive alternative, but feline-specific data in naturally occurring OM are lacking. Because the feline TB is divided into a dorsolateral (DLC) and ventromedial compartment (VMC), US can only visualize the VMC, raising concerns about underdiagnosis. This study evaluated the diagnostic performance and clinical feasibility of bulla ultrasound (BUS) in cats compared with CT/MRI.

Methods

A prospective, cross-sectional study enrolled 32 client-owned cats (64 ears) undergoing CT or MRI of the head for routine clinical indications (2022–2024). BUS was performed by a blinded radiologist, primarily in awake or lightly sedated cats, with a ventral transducer approach imaging the VMC. Findings were categorized as air (reverberation artifact), fluid (hypoechoic region with visible septum bulla), or acoustic shadow (osseous thickening). CT/MRI served as the gold standard. Sensitivity, specificity, predictive values, and accuracy were calculated.

Results

Of 64 ears, CT/MRI identified 39 as air-filled and 25 with fluid. BUS detected air in 41, fluid in 22, and acoustic shadowing in one ear. Two false negatives occurred when only scant fluid was present. After excluding the acoustic shadowing case, BUS achieved sensitivity 92%, specificity 100%, positive predictive value 100%, negative predictive value 95%, and accuracy 97%. The mean BUS duration was 3.5 minutes; 23 cats were imaged awake, most tolerating the procedure well with or without oral anxiolytics (gabapentin). Bilateral OM (67%) was more common than unilateral. Acoustic shadowing correlated with chronic OM and TB wall thickening.

Limitations

All BUS examinations were performed by a board-certified radiologist; generalizability to practitioners with less imaging expertise is unknown. DLC-only OM was not observed, so the risk of underdiagnosis remains theoretical. Otoscopic exams were variably performed, preventing calculation of otoscopy’s diagnostic performance. No cats had soft tissue masses in the VMC, so differentiation between fluid and mass could not be evaluated.

Conclusions

BUS is a rapid, well-tolerated, and highly accurate tool for detecting OM in cats, reliably distinguishing fluid from air in the VMC. While it cannot replace CT/MRI for staging or detecting DLC-only disease, it offers a valuable, non-invasive point-of-care screening tool. Acoustic shadowing may be an additional ultrasonographic marker of chronic OM. Combined BUS and otoscopy may enhance diagnostic accuracy in clinical practice.

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