The Role of Intraoperative Neurophysiological Monitoring (IONM) in Brainstem Cavernous Malformation Surgery

Introduction: Intraoperative neurophysiological monitoring (IONM) is widely used to predict and minimize neural damage during neurosurgery. Brainstem cavernous malformation (BSCM) surgery is challenging with high postoperative neurologic deficit risk. We aimed to investigate how the use of IONM affect the results of BSCM surgery.

Methods: This is a retrospective, single-center, single-surgeon study that includes patients’ data who underwent surgery for BSCM in the past 7 years. Demographic parameters, lesion location and size, intraoperative electroencephalography (EEG), somatosensory (SSEP), motor (MEP) and brainstem auditory evoked potential (BAEP) recordings, early/late postoperative modified Rankin Scale (mRS) and neurological exam changes, complications and extent of resection parameters were collected.

Results: A total of 105 cases (53 female) were included. The mean age 43.2±16.1 years and the mean BSCM diameter was 1.7±0.7cm. The majority of the BSCMs were located in the pons (63.8%). EEG and SSEP recordings were available in all, MEP in 46 and BAEP in 67 patients. No EEG change was observed in any patient. SSEP monitoring showed temporary disturbance in 7 (6.7%), permanent changes in 25 (23.8%) patients. MEP signals decreased temporarily in 3 (6.5%), permanently in 6 patients (13% of 46 available). BAEP was disturbed temporarily in 9 (13.4%), permanently in 18 (26.9% of 67 available) patients. The complete resection rate was 99% with no surgical mortality. While 47.6% had worsening mRS in the immediate postoperative period, permanent operative morbidity rate was 12.9%. There was a significant association between permanent SSEP change and permanent long-term morbidity (p=0.019).

Conclusion : IONM is a valuable tool to guide safe resection and predict postoperative neurological deterioration in BSCM surgery. However, given that most temporary and some permanent changes do not translate into long-term morbidity, these alterations should be interpreted judiciously and not preclude complete resection in BSCM surgery, where leaving a remnant may potentially lead to catastrophic outcomes.