Radiographic Predictors of Serviceable Hearing Preservation in Vestibular Schwannomas

Introduction: Hearing preservation remains a critical goal in vestibular schwannoma (VS) surgery, yet predicting functional outcomes after resection is challenging. The Koos grading scale is the most commonly used system to describe VS size and anatomical extent. Although it defines tumor extension within the internal auditory canal (IAC), extrameatal space, and brainstem compression—features essential for surgical planning—it lacks quantitative measures and does not reliably predict postoperative functional outcomes. Tumors within the same Koos grade can vary significantly in spatial morphology and compartmental extension. While smaller tumors (Koos I) generally yield higher hearing preservation rates, reported rates for Koos III and IV tumors range from 0% to 30%. Thus, although Koos grading provides a general framework, it fails to capture subtle anatomic features critical for cranial nerve preservation. We evaluated how specific radiographic measures and Koos grade relate to postoperative hearing preservation. Methods: We retrospectively analyzed 75 consecutive patients with sporadic VS and serviceable preoperative hearing (AAO-HNS class A/B) who underwent microsurgical resection via retrosigmoid or middle fossa approach. Preoperative MRI determined Koos grade, allowed for radiographic measurement such as intracanalicular tumor length, and the presence of a fundal fluid cap. Serviceable hearing preservation defined as postoperative AAO-HNS class A or B. We performed univariate analyses comparing patients with and without preserved hearing, and multivariate logistic regression to identify independent predictors, adjusting for age, tumor size, fundal cap, and surgical approach. Results: Seventy-five patients with VS and serviceable hearing (class A, n = 48; class B, n = 27) underwent resection. The mean pure tone average was 25.8 ± 12.2 dB, and median word recognition score was 96% (IQR 92–100). Approaches included retrosigmoid ( n = 55) and middle fossa ( n = 20). Median follow-up was 13 months (range 1–82). Serviceable hearing was preserved in 29.3% ( n = 22). Postoperative good facial nerve function (House–Brackmann I–III) was achieved in 94.7%. On univariate analysis, Koos I–II tumors (OR 3.22; 95% CI: 1.09–9.52[JB1]), shorter overall tumor length (OR 0.91; 95% CI: 0.84–0.97), smaller cisternal diameter (OR 0.94; 95% CI: 0.89–0.99), and shorter intracanalicular length (OR 0.82; 95% CI: 0.68–0.99) correlated with hearing preservation. On multivariate analysis, only Koos I–II tumors (OR 3.88[JB2] ; 95% CI: 1.16–12.94; p < 0.01) and shorter intracanalicular length (OR 0.77; 95% CI: 0.62–0.96; p < 0.01) independently predicted hearing preservation. Presence of a fundal cap, surgical approach, and extent of resection did not significantly influence outcomes. Conclusion: Radiographic measures such as overall tumor length and intracanalicular extension, in addition to Koos grade, correlate with hearing preservation after VS resection. Patients with small tumors (Koos I–II) demonstrated significantly higher hearing preservation rates than those with larger tumors (Koos III–V, OR 3.88, p < 0.01). Intracanalicular tumor length inversely associated with hearing preservation, as shorter IAC involvement favored retained hearing (OR 0.77, p < 0.01), independent of Koos grade. Updating the Koos classification to incorporate quantitative predictors such as intracanalicular tumor length could enhance prognostication, improve patient counseling, and refine surgical planning to optimize functional outcomes. Publication History Article published online: 27 February 2026 © 2026. Thieme. All rights reserved. Georg Thieme Verlag KG Oswald-Hesse-Straße 50, 70469 Stuttgart, Germany