(846) Evaluation of Cochlear Dead Regions in Vestibular Schwannoma Using the Threshold Equalizing Noise Test

Introduction: Hearing loss in vestibular schwannoma (VS) has traditionally been attributed to neural compression by the tumor; however, recent evidence suggests cochlear toxicity mediated by tumor-secreted factors. Despite these findings, the prevalence and characteristics of inner ear dysfunction in VS remain incompletely understood. Cochlear dead regions (CDRs) reflect localized cochlear dysfunction and can be identified using the Threshold Equalizing Noise (TEN) test. This study aimed to evaluate the prevalence and characteristics of CDRs in patients with VS.

Methods: This retrospective clinical study included 48 untreated patients with vestibular schwannoma who underwent Threshold Equalizing Noise (TEN) testing at a single academic institution between 2020 and 2025. Pure-tone average (PTA), speech discrimination score, American Academy of Otolaryngology–Head and Neck Surgery (AAO-HNS) hearing class, and tumor size (Koos classification) were analyzed. The presence of cochlear dead regions was determined using standard TEN test criteria, and associations with audiological and clinical variables were evaluated.

Results: Cochlear dead regions (CDRs) were identified in 20 of 48 patients (41.7%). The prevalence of CDRs did not show a clear association with tumor size (Koos I–IV), with the highest proportion observed in Koos I tumors (46.7%). CDRs were more frequently detected in patients with poorer hearing, with a significantly higher prevalence in those with PTA ≥50 dB compared with PTA < 50 dB (66.7% vs. 28.6%). According to the AAO-HNS hearing classification, CDRs were most prevalent in class C (85.7%) but were also observed in class A and B patients.

Conclusions: Approximately 40% of patients with vestibular schwannoma exhibited cochlear dead regions, independent of tumor size. Cochlear dead regions were observed even in patients with mild hearing loss and favorable AAO-HNS hearing classes, suggesting that cochlear involvement may occur in early-stage vestibular schwannoma and that Threshold Equalizing Noise testing may detect subclinical inner ear dysfunction.