Is Cochlear Implantation Effective for Auditory Rehabilitation Following Vestibular Schwannoma Treatment?

Abstract

Hearing loss in patients with vestibular schwannoma (VS), before and after treatment, is known to negatively impact quality of life. A variety of treatment options are available for auditory rehabilitation. Contralateral routing hearing aids (CROS) and osseointegrated conduction devices can shuttle the auditory stimuli to the contralateral ear after treatment in unilateral vestibular schwannoma patients but cannot improve sound localization. Auditory Brainstem Implantation (ABI) is approved by FDA for patient 12 years and older with Neurofibromatosis Type 2 (NF2) and open-set speech after ABI is an exception rather than the rule.1 Increasingly, cochlear implantation (CI) is being recognized as a feasible option in VS patients. In this Triological Society Best Practice, we review the current evidence to determine if CI is an effective intervention for auditory rehabilitation after VS treatment. The largest systematic review to date on CI outcomes following VS resection was published by Wick et al.1 They identified 93 patients across 29 studies that met their inclusion criteria and compared open-set speech and daily device usage between two patient groups. The first group included 46 patients that underwent translabyrinthine (TL) VS resection with simultaneous CI. The second group included 47 patients who underwent delayed CI after tumor resection by TL, middle fossa (MF), or retrosigmoid (RS) approaches with variable time delays to CI across cases. Some of these patients underwent placement of dummy prosthesis to mitigate cochlear obliteration per surgeon preference, while others did not. Authors identified a high degree of heterogeneity in reporting of CI postoperative outcomes between different studies, which was attributed to differences in language and institutional protocols. Four cases were reportedly noted to have cochlear fibrosis causing difficulty with lead insertion, all of these were in the delayed group. Overall, they reported that open-set mean word scores of 52% and 37.9% in the simultaneous and delayed groups, respectively. The mean sentence scores were 65.4% in the simultaneous CI group versus 49.6% in the delayed group. About 70% of NF2 patients reported lower daily CI usage compared to 93% sporadic VS group negatively influencing their CI performance. Subsequently, Dahm et al. studied the value of electrical auditory brainstem response (eABR) testing on patients undergoing simultaneous VS resection and CI.2 The study included five patients with unilateral sporadic VS who underwent TL VS resection. Two patients had a history of presbycusis, one patient had undergone previous RS resection for VS, and another had previous stereotactic radiosurgery (SRS). Preoperative eABR was completed using a trans-tympanic promontory electrode, and it was positive in all tested patients. Intraoperative eABR testing was also performed and was negative in three of five cases after tumor resection. Nonetheless, all five patients underwent CI. Only one of three patients with negative intraoperative eABR subsequently had auditory perception. Three out of five patients were reported as daily users with open-set speech recognition at 12 month follow-up. Four out of five patients in this small cohort completed quality of life (QoL), Speech, Spatial and Qualities of hearing scale abbreviated-12 (SSQ12), the Assessment of Quality of Life-8D (AqoL-8D) and the Tinnitus questionnaires (mini-TQ). The SSQ12 showed an increased or stable hearing specific QoL; the AqoL-8D showed an increase in all patients. The mini-TQ showed more or less stable results except in one patient who had an increase in the score after CI. Authors concluded that CI was a promising option with a favorable complication profile for sporadic vestibular schwannoma patients and that preservation of eABR response following surgical resection predicted good outcome. In 2021, Deep et al. published a retrospective series on CI outcomes in 24 NF2 patients with a mean follow-up of 4 years.3 Of the 24, 12 patients underwent microsurgical VS resection by TL, RS, or MF approach, while the other 12 patients were either observed or underwent SRS. One surgical patient underwent simultaneous CI, while the rest underwent delayed implantation. The inclusion criteria for CI were the presence of an intact cochlear nerve and presence of T2 signal in cochlea. Eight of the 12 surgery patients achieved postoperative open-set speech recognition with mean word score of 43%. Of note, three of those eight patients experienced tumor growth and subsequently lost CI functionality at later follow-up. Partial obliteration of the cochlea was encountered in three cases with reduced preoperative T2 MRI signal. The time delay to their implantation was quite variable, ranging from 6 months to 10 years. The authors concluded that while nonoperative therapies may yield better hearing outcomes for NF2 patients with larger tumors, CI are effective if the cochlear nerve is intact regardless of the modality of tumor management. In addition to presence of eABR and intact cochlear nerve, Patel et al. reported that the presence of fluid signal in the cochlea on T2-weighted MRI is also a predictor of better CI outcome. They studied nine patients with sporadic VS and 13 with retrocochlear pathologies (neurosarcoidosis, pontine stroke, and head neck malignancies post irradiation) who underwent CI with a mean follow-up of 2 years.4 All patients had cochlear fluid signal on imaging and intact cochlear nerve by preoperative promontory stimulation testing; intraoperative electrical testing was not performed. Of the nine patients with sporadic VS group: four underwent TL or MF resection with simultaneous CI and five underwent SRS or observation and CI. A mean Consonant Nucleus Consonant (CNC) word score of 55% post-CI was achieved in patients with retrocochlear pathologies compared to 18% in two sporadic VS patients with follow-up of less than 6 months post-activation. Of the other seven sporadic VS patients, two were nonusers, two used CI for less than 6 hours daily and no data were available for three patients. The authors concluded that patients with sporadic VS exhibited guarded hearing outcomes compared to those with non-VS retrocochlear pathologies. Similarly, Medina et al. investigated the impact of intact cochlear nerve on CI outcome in 14 patients that underwent TL VS resection with simultaneous CI; mean follow-up was 12 months.5 To assess nerve function, they used a disposable intracochlear test electrode to perform intraoperative eABR testing. Nine of 14 patients had positive eABR after resection and all of them obtained auditory perception, defined as sound detection at 50 dB or below, with their simultaneous CI. Only one of five patients with negative intraoperative eABR testing had auditory perception with their CI. The authors concluded that eABR is a useful tool to complement surgeon decision-making regarding implantation after VS resection. Although CI is feasible, only some patients can achieve open-set speech recognition. The presence of cochlear fluid signal on T2-weighted MRI, presence of an intact, functioning cochlear nerve, and positive eABR test following tumor resection may assist in predicting CI outcomes. CI outcome data following treatment for VS are highly variable and there are paucity of quality of life studies in this group of patients. Objective patient reported outcome measures and quality of life data are needed to counsel patients and set realistic expectations about CI outcomes in VS patients. The several case series mentioned in this article each represent level IV clinical evidence. The systematic review which includes both case series and case reports, also represents level IV clinical evidence. Larger scale prospective randomized controlled trials (RCTs) with standardized preoperative and postoperative testing and follow-up are needed. We thank Dr Nathan, Chairman, Dept of Otolaryngology and Head Neck Surgery, LSU Health, Shreveport, for her encouragement and support.