Facial Nerve Conduction Block during Vestibular Schwannoma Surgery: A Rare and Unclarified Transient Neural Dysfunction

Preservation of facial nerve function while achieving sufficient tumor removal is a key objective in vestibular schwannoma surgery, and continuous facial nerve monitoring provides real-time, quantitative, and functional assessment of facial nerve during resection. In our experiences of more than 1,900 vestibular schwannoma surgeries, we have occasionally observed an abrupt and marked decrease in monitoring amplitude without any high-risk manipulation such as direct nerve dissection. This rare phenomenon, illustrated by 2 recent cases in this study, was transient or unrelated to postoperative facial nerve dysfunction, suggesting a mechanism distinct from structural nerve injury. One plausible explanation is a temporary conduction block caused by factors such as local ischemia, torsional stress, or changes in the microenvironment of the nerve. Recognition of this event is clinically important because a decrease in amplitude may prompt unnecessary discontinuation of resection or consideration of nerve reconstruction if misinterpreted as irreversible facial nerve injury. Differentiating conduction block from true injury requires careful correlation with surgical context, nerve anatomy, and subsequent amplitude recovery. Awareness of this pattern can help maintain appropriate surgical progress while minimizing the risk of facial nerve injury. Continuous facial nerve monitoring, by detecting such sudden changes in real time, not only supports safe tumor removal but also enhances intraoperative decision-making in complex vestibular schwannoma surgery.