Intraoperative vagal nuclei mapping for a safe entry point in lower brainstem cavernoma

Intraoperative vagal nuclei mapping for a safe entry point in lower brainstem cavernoma B. Almasarwah1, D. Giakoumettis1, E. Chiotaki2, P. Pittaras1, G. Vavoulis1, T. Vogiatzoglou1, K. Vlachos1 1Department of Neurosurgery, KAT General Hospital, Athens, Greece 2Consultant in Intraoperative Monitoring, Atron Health, Athens, Greece Objective: Cerebral cavernous malformations are neurovascular low-flow lesions and occur in the brainstem up to 35% of cases. Because brainstem cavernous malformations (BSCMs) can grow and bleed spontaneously, they present considerable risk of severe neurological deficit. Consequently, it is reasonable to undergo microsurgical removal of BSCMs to relieve mass effect and prevent repetitive bleeding. Operative procedures on the brainstem remain challenging and to facilitate BSCM removal while decreasing the substantial risk of iatrogenic deterioration, there is a need for functional real-time monitoring (e.g., intraoperative neuromonitoring [IONM]). Methods: We report the case of a 24-year-old female patient who presented with cavernous malformation of the left medulla oblongata. The patient underwent brainstem surgery with IONM and vagal nuclei neuromonitoring to identify a safe entry zone. Results: A combined midline suboccipital and far-lateral approach was designed and the cerebellar tonsils, the left cerebellar hemisphere, and the lateral and posterior surfaces of the medulla oblongata were exposed. Intraoperative mapping of brainstem nuclei was applied to identify a safe entry zone. Direct low-current frequency stimulation of the vagal nuclei helped confirming the entry zone at the visually noticed bulge. Medullotomy was made under neuromonitoring and the BSCM was reached and completely resected without new neurological deficit shown in IONM. The patient showed a good recovery with no deficit in the 3-month post-op follow-up. Conclusions: The application of IONM during BSCM surgery is useful in preventing postoperative new neurological deficit. The direct low-current frequency stimulation of the vagus nerve nuclei helped in identifying a safe entry zone in the brainstem of the case.