Abstract
Recently, intraoperative monitoring of the motor evoked potential (MEP) has become essential during aneurysm surgery to avoid the occurrence of motor deficit. The MEPs are commonly recorded from upper or lower limb muscles after electrical stimulation of the motor cortex. On the other hand, we monitor the MEPs recorded from the spinal cord at the cervical epidural space after the electrical stimulation of the motor cortex during aneurysm surgery. In this study, we describe the usefulness of corticospinal MEP monitoring in aneurysm surgery. Corticospinal MEPs were recorded in 31 patients during aneurysm surgery. Twenty-two patients had internal carotid artery aneurysms, including 12 ruptured aneurysms, and 17 patients had middle cerebral artery aneurysms, including 10 ruptured aneurysms. Preoperatively, an epidural lead for the MEP recording was inserted into the cervical epidural space under radiographic guidance and under general anesthesia with muscle relaxants. After craniotomy, a subdural grid was placed over the sensory and motor cortices and optimum contacts for the electrical stimulation were selected according to the waveforms of somatosensory evoked potentials. Corticospinal MEPs, which were elicited by cortical stimulation and consisted of a D-wave followed by 2 or 3 I-waves were recorded from an epidural lead (bipolar recording). Among these 31 patients, 11 (35.5%) had changes in MEPs. An amplitude reduction less than 50% of the control was observed in 6 patients. An amplitude augmentation of more than 50% was also observed in 5 patients. These MEP changes recovered to the control level after the release of temporary clip or reclipping of aneurysms. MEP monitoring thereby prevented motor deficits. Corticospinal MEPs were constantly recorded and they showed a sensitive response to the blood flow insufficiency of the arteries during aneurysm surgery. Corticospinal MEP monitoring is therefore considered to safely and effectively prevent motor deficits caused during aneurysm surgery.
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