Frequency-Specific hearing changes in vestibular schwannoma and the greater sensitivity of ABR in small tumors

BACKGROUND: Vestibular schwannoma (VS) is a benign vestibular nerve tumor. The association between tumor size and auditory dysfunction, especially in small VSs, remains unclear. OBJECTIVES: To assess audiological changes with increasing tumor size in VS and identify tumor-size thresholds related to hearing impairment. MATERIAL AND METHODS: We retrospectively analyzed 430 patients with sporadic VS treated between 2008 and 2025. Patients were classified by Koos grade. Clinical features, pure-tone audiometry, speech discrimination score, auditory brainstem response (ABR), and magnetic resonance imaging findings were reviewed. Multivariate regression and receiver operating characteristic analyses were performed. RESULTS: Annual detection of small VS (Koos I-II) increased substantially. Hearing deteriorated with rising Koos grade, showing high-frequency impairment. Pure-tone and speech discrimination were comparable between Koos I and II, whereas ABR differed significantly; over 60% of Koos I patients with serviceable hearing had abnormal ABR. ROC identified thresholds of 17.4 mm for loss of serviceable hearing and 13.4 mm for ABR abnormality. CONCLUSIONS AND SIGNIFICANCE: Audiological impairment worsens progressively as VS growth, with clear differences between small and medium-to-large tumors. ABR has superior sensitivity for early retrocochlear dysfunction in small VS and may serve as a preoperative predictor for hearing preservation to support clinical decision-making.