Two Cases of Intraoperative Hearing Monitoring in Non-Small Acoustic Neuroma and Literature Review

doi:10.11850/j.issn.1009-122X.2025.10.009

Abstract：Objective To summarize the experience of multi-mode hearing monitoring applied during surgery for non-small acoustic neuroma (AN). Methods Two cases of AN patients with maximum tumor diameter exceeding 2.0 cm were retrospectively analyzed. During the operation, auditory brainstem response (ABR), electrocochleography (ECochG), and cochlear nerve compound action potential (CNAP) were combined to monitor hearing function. The intraoperative monitoring experience was summarized, and relevant literature on the application of the three monitoring methods in AN surgery was reviewed. Results The preoperative hearing of the two patients was classified as D grade and A grade according to the American Academy of Otolaryngology-Head and Neck Surgery (AAO-HNS) classification system. For the D-grade patient (Case 1), the CNAP wave at the brainstem end was present at the end of the operation. For the A-grade patient (Case 2), the AP wave of ECochG and the CNAP wave at the brainstem end were present at the end of the operation. Postoperative hearing assessment within 8 days or 2 weeks and 1 year after surgery remained D grade for both patients. Conclusion ABR, as a traditional monitoring method, can objectively reflect the integrity of the auditory pathway, but has limitations during intraoperative use. ECochG reflects the functional status of the cochlea and the distal part of the cochlear nerve. CNAP cannot reflect the status of the brainstem portion of the auditory conduction pathway. Especially for non-small AN, even with the combination of three monitoring modes, it is still possible that hearing preservation is not ideal. However, during the operation, the anatomical integrity of the auditory pathway, especially the cochlear nerve, should be protected as much as possible to preserve the opportunity for subsequent cochlear implantation.