Significance of wave I loss of brainstem auditory evoked potentials during microvascular decompression surgery for hemifacial spasm

Objective: We sought to define the significance of wave I loss of brainstem auditory evoked potentials (BAEPs) during microvascular decompression (MVD) surgery for hemifacial spasm. Methods: Out of 670 patients, 36 showed wave V loss during MVD surgery. These patients were classified into the following two groups based on wave I loss: Total wave loss, including wave I loss, and wave V loss with persistent wave I. We analyzed the differences in postoperative complications between the groups. We also investigated when wave I loss occurred during MVD surgery. Results: Of the 36 patients, 24 (66.7%) exhibited wave I persistence and 12 (33.3%) exhibited total wave loss. The patients who showed total wave loss were significantly more likely to exhibit postoperative hearing loss (p = 0.009). In addition, these patients exhibited a significantly higher frequency of postoperative complications such as dizziness and tinnitus (p = 0.002 and p = 0.031, respectively). Total wave loss occurred more frequently after the decompressive procedure of MVD surgery. Conclusions: Total wave loss, including wave I loss, was more closely associated with severe postoperative complications. Total wave loss occurred more frequently after the decompressive procedure of MVD surgery. Significance: These findings suggest the significance of wave I loss of BAEPs.