We investigated the usefulness of motor evoked potential (MEP) for detecting the cerebral blood flow insufficiency (BFI) during aneurysm surgery.
The study population consisted of 269 patients with intracranial aneurysms who underwent surgery via a standard frontotemporal craniotomy. After the dura mater had been opened, a grid electrode strip with 16 small electrodes was inserted subdurally into the hand motor cortex from the edge of the craniotomy. The hand motor cortex was stimulated by short train stimuli. The MEPs were recorded from the contralateral thenar muscles in all but 3 patients who had severe preoperative motor paresis. We evaluated intraoperative MEP findings, causes of MEP changes and motor outcomes in the 266 patients in whom MEPs could be recorded. Out of 232 patients whose MEP remained unchanged, one developed mild and transient hemiparesis, and the other 231 had no postoperative motor paresis. Thirty-two of the other 34 patients manifested transient MEP changes. The transient MEP changes were thought to be attributable to BFI of the cortical branches in 4 patients, of the perforating artery in 15, and of either the cortical branches or the perforating artery in 13 patients. Of these 32 patients, 24 did not show any postoperative motor paresis; transient motor paresis was recognized in the other 8. In 2 patients, MEP disappeared and did not recover. These patients developed severe hemiparesis, and a postoperative CT scan revealed a new low-density area in the corona radiata, putamen and internal capsule.
The findings of this study suggest that the monitoring method introduced here is safe and reliable for detecting intraoperative BFI in both the perforating artery and cortical branches. MEP monitoring is useful in preventing postoperative motor paresis in aneurysm surgery.
