Histopathological Considerations for Indication of Cochlear Implant for Patients with Vestibular Schwannoma

Objective: When determining candidacy for cochlear implantation (CI) in patients with vestibular schwannoma (VS), not only hearing thresholds but also the integrity of cochlear and neural structures are important. This study aimed to clarify the conditions under which CI is likely to be effective by examining the relationship between pathological findings in cochlear and neural structures and premortem audiometric data—including pure-tone average (PTA) and speech discrimination score (SDS)—in various VS cases, including post-surgical specimens.

Methods: Pathological specimens were obtained from an institutional Temporal Bone Registry. Ultimately, 34 specimens from 28 patients were included for analysis, five patients had neurofibromatosis 2. Clinical data including audiometric results, surgical history, and surgical approach were reviewed. Pathological assessment of hematoxylin and eosin–stained temporal bone sections examined the presence of residual tumor, tumor invasion into the fundus, and the condition of spiral ganglion cells (SGCs) and cochlear hair cells. These pathological findings were then correlated with premortem clinical and audiometric data.

Results: Of the 29 patients included, seven were managed non operatively; the remaining underwent VS resection either via middle fossa craniotomy (MFC, 4), retrosigmoid/retrolabaryntine (RS/RL, 5) or translabaryntine (TLC,15) approach. Several cases demonstrated preserved SGCs despite severe hearing loss on PTA, whereas cases with low SDS typically showed significant SGC loss (Figue 1). Severe loss of hair cells and SGCs was also observed after TLC or prolonged hearing loss. All cases with tumor invasion into the fundus demonstrated marked SGC degeneration. Conversely, cases with preserved hearing had clear survival of SGCs. Along the same lines, post-surgical cases without fundal residual showed SGCs and hearing preservation.

Conclusion: This study demonstrates that SDS reflects the preservation of SGCs and neural structures in VS patients, making it a useful indicator for evaluating CI candidacy. Severe hearing loss and fundal invasion are associated with irreversible cochlear neural degeneration, predicting likely poor postoperative CI outcomes. Additionally, early loss and progressive degeneration of hair cells and SGCs were observed after TLC, suggesting afferent nerve dysfunction contributes to cochlear neural degeneration. These findings highlight the importance of timely tumor resection, with focus on removal of fundal tumor.

[Fig. 1] Pathological specimen in patients managed non-operatively (top), with inner-ear preserving surgery (middle), or translabaryntine surgery (bottom). Top: left specimen with well-preserved cochlear structures, with spiral ganglion cell counts exceeding 20,000 and well preserved hair cells in all cochlear turns,, in comparison to right specimen with poor structural preservation with tumor invasion into fundus. Middle: Post operative hearing function associated with degree of preservation of cochlear structures, SGC and hair cells. Bottom: Structural preservation early after TLC but significant cochlear ossification and cell loss seen years after surgery. For each specimen: Left – Overall view of the cochlea; Center – SGC; Upper right – Hair cells in the apical turn; Middle right – Hair cells in the middle turn; Lower right – Hair cells in the basal turn. PTA: Pure Tone Average, SDS: Speech Discrimination Score, SGC:Spiral ganglion cells, MFC: Middle Fossa Craniotomy, RS:Retrosigmoid Approach, TLC: Translabyrinthe Craniotomy.

Publication History

Article published online:
27 February 2026