Is Transient Mixed Hearing Loss a Distinct Audiometric Feature in Patients With Inner Ear Schwannoma?

Objective: To characterize the transition of audiometric features in patients with inner ear schwannoma (IES) with a special focus on transient mixed hearing loss.

Patients: Twelve patients were clinically diagnosed with an IES.

Interventions: All patients underwent otoscopic and audiological examinations, including serial pure-tone audiometry and magnetic resonance imaging (MRI) scans. Additional audiometric measurements, including impedance audiometry, distortion product otoacoustic emissions, speech audiometry, and auditory brainstem responses were performed in selected patients.

Main Outcome Measures: All available audiograms were reviewed, and the configuration patterns, type of hearing loss, and air-bone gaps were analyzed. The relationship between audiometric features and radiologically identified tumor locations was examined.

Results: On the initial audiograms, 5 (41.7%) of the 12 patients showed U-shaped configurations, and 4 (33.3%) showed rising configurations. Serial audiograms demonstrated transient mixed hearing loss with air-bone gaps, predominantly in the low to mid frequencies in 9 (75.0%) patients, despite normal otoscopic findings. The incidence of mixed hearing loss (75.0%) was significantly higher than that of other inner ear disorders (4.1-12.8%). Progressive deterioration of hearing thresholds was observed in all patients, with severe-to-profound hearing loss in 11 (91.7%) patients.

Conclusions: In the early stage, the most common audiometric features in patients with IES are sensorineural hearing loss with a U-shaped or rising configuration with air-bone gaps at low to mid frequencies, followed by rapidly progressive hearing deterioration. Transient mixed hearing loss appears to be a distinct audiometric feature of patients with IES.