Intraoperative Neurophysiological Monitoring During Adult Brainstem Glioma Resection: Association Between Electrophysiological Changes and Early Neurological Outcome

Intraoperative neurophysiological monitoring (IONM) is widely used during brainstem surgery to reduce the risk of neurological injury, although its prognostic value in adult brainstem glioma (BSG) surgery remains unclear. We retrospectively analyzed 22 consecutive adults who underwent surgery for BSGs with multimodal IONM between 2010 and 2023. Monitoring included somatosensory evoked potentials (SSEPs), motor evoked potentials (MEPs), brainstem auditory evoked potentials (BAEPs), corticobulbar MEPs (CoMEPs), and cranial nerves electromyography. The primary endpoint was the association between intraoperative neurophysiological changes and postoperative neurological functional status at hospital discharge, assessed with the modified McCormick Scale (mMCS). Secondary endpoints included postoperative complications and length of hospital stay. SSEP warning criteria were met in 10 patients (45.5%), while 10 patients (45.5%) experienced a ≥50% reduction in MEP amplitude in at least one monitored muscle. Despite these findings, neither SSEP nor MEP amplitude changes were significantly associated with postoperative neurological status. Transcranial MEP stimulation thresholds increased significantly during surgery (p = 0.007), and threshold elevation was associated with postoperative complications (Kendall’s τ = 0.498, p = 0.007). BAEP recordings remained stable throughout all procedures. Conventional amplitude-based IONM changes were not associated with early neurological outcome after adult BSG resection. In contrast, increases in MEP stimulation threshold may represent a sensitive indicator of postoperative complications. Further prospective studies are warranted.