Histopathologic Considerations for Indication of Cochlear Implant for Patients With Vestibular Schwannoma

Objective: Predicting cochlear implant (CI) outcomes in patients with vestibular schwannoma (VS) is challenging, even when the cochlear nerve remains anatomically intact. This study examined how cochlear and neural pathology relate to premortem audiometric findings, pure-tone average (PTA) and speech discrimination score (SDS), to explore histopathologic conditions that may be relevant to CI candidacy. Methods: Temporal bones labeled as “acoustic neuroma” were selected from the House Ear Institute Temporal Bone Registry. Twenty-eight patients (34 ears) with well-preserved cochlear structures were included. Clinical data, including audiometry, surgical history, and surgical approach, were reviewed. Histologic analysis assessed residual tumor, fundal involvement, and the status of cochlear hair cells and spiral ganglion cells (SGCs). Pathology was correlated with clinical and audiometric features. Results: Among 34 specimens from 28 patients, 7 were from nonsurgical cases and 27 from surgical cases. In cases with preserved hearing (PTA ≤60 dB or SDS ≥60%), spiral ganglion cell (SGC) counts exceeded 20,000, and hair cells were well preserved. Cases with severe PTA elevation commonly showed hair cell injury, yet SGCs remained partially preserved. In contrast, reduced SDS was consistently associated with SGC loss. After a translabyrinthine approach, SGCs and hair cells were nearly absent within 3 to 27 months in most cases, and cochlear ossification was observed in cases surviving beyond 50 months. In all cases with tumor extension into the fundus of the internal auditory canal, hearing was completely lost, and both hair cells and SGCs showed severe degeneration. Conclusion: SDS may parallel SGC status in VS, possibly more closely than PTA. These findings suggest that early tumor removal before fundal extension and preservation of the cochlear nerve may be associated with cochlear and neural integrity, which could be relevant for future CI candidacy.