Objective: Auditory nerve monitoring through electrically evoked compound action potentials (eCAP) can be used to assess cochlear neural integrity during vestibular schwannoma (VS) resection. Herein, we report on 5 cochlear implant (CI) patients who underwent VS resection with present eCAP responses both intraoperatively and postoperatively. Patients either did not perceive any sound through their CI or rapidly adapted to electrical stimulation, suggesting that the presence of eCAP does not guarantee auditory nerve function in patients with VS resection. Patients: Five patients who underwent simultaneous VS translabyrinthine resection and cochlear implantation. Interventions: Simultaneous cochlear implantation and translabyrinthine microsurgical VS resection. Main outcome measure: Electrically evoked compound action potential. Results: All patients had eCAP responses present during their VS resection and for at least 50 days post-surgery. Three of the 5 patients did not perceive any sound with their cochlear implant. This shows that the presence of an eCAP alone does not guarantee a functional auditory nerve or auditory perception. The other 2 patients could hear non-speech sounds, but these sounds quickly became inaudible, indicating that their auditory nerve lacked the ability to integrate the electrical stimulus over time. Conclusions: The presence of an eCAP response does not guarantee auditory sensation through a CI. Although eCAP measurements provide insight into the function of the distal end of the nerve, it does not ascertain integrity or function of the larger auditory nerve pathway. Therefore, eCAPs should not be used in isolation to monitor auditory nerve function during VS resection.
Kolberg et al. (2026) studied this question.