Role of Intraoperative Monitoring in Cerebrovascular Surgery

Object: Here, we evaluated the role of various methods of intraoperative monitoring in cerebrovascular surgery. Materials and Methods: A total of 263 patients underwent cerebrovascular surgery using intraoperative monitoring after the introduction of a 16-channel Neuromaster. There were 229 cerebral aneurysm (85 ruptured, 144 unruptured), five arteriovenous malformation (AVM), 19 bypass, seven carotid endarterectomy (CEA), and three cavernous angiomas cases. Motor-evoked potential (MEP), somatosensory-evoked potential (SEP), and visual-evoked potential (VEP) were selected considering the pathogenesis types and sites. MEP contained transcranial and direct cortical stimulation and SEP, median nerve (upper extremity) and posterior tibial nerve (lower extremity) stimulation. Bilateral regional saturation of oxygen (rSO2) using near-infrared spectroscopy (NIRS) was also monitored in patients who underwent CEA. Results: Intraoperative monitoring was successfully performed in all 263 cases. MEP could not be recorded and an upper-extremity SEP was performed in three cases because of preexisting hemiparesis. In 15 cases, MEP disappeared after temporary occlusion of the parent artery or aneurysmal clipping but reappeared after release of the temporary occlusion or re-clipping; one patient whose MEP amplitude recovered to 50% of the control developed transient hemiparesis (4/5). Another two patients, in whom the MEP disappeared until the end of surgery, developed permanent hemiparesis (4/5). In a patient with a posterior cerebral artery (PCA) aneurysm, VEP was transiently decreased after temporary PCA occlusion. In a patient with the premotor AVM, the MEP was transiently decreased after the precentral artery was temporarily occluded. In a patient with an occipital cavernous angioma, the VEP transiently decreased after dissection around the posterior horn and the patient was discharged from the hospital without any visual field disturbances. Three patients with CEA in whom the transcranial MEP and upper extremity SEP decreased, recovered after insertion of the internal shunt. Conclusions: In cerebrovascular surgery, various methods of monitoring enable us to detect intraoperative ischemia and feedback to the operative maneuvers.