Abstract
Changes in the somatosensory evoked potentials (SEPs) were monitored during the application of temporary clips in 97 aneurysm procedures. SEPs in response to median nerve stimulation were used as an index of cortical function. Aneurysm locations were as follows: middle cerebral artery (MCA): 46 cases, internal carotid artery (ICA): 51 cases.The period of temporary occlusion ranged from 2 minutes to 70 minutes, and the mean occlusion time was 20.3 minutes at the M1 segment of MCA and 15.8 minutes at the cervical ICA.In 8 patients with MCA aneurysms and 33 patients with ICA aneurysms, no changes in SEPs during temporary occlusion were seen. Among these 41 patients, however, there were 3 patients with postoperative motor deficits (false negative), 2 of which improved markedly within a few days.In 14 patients (8 MCA aneurysms, 6 ICA aneurysms), temporary occlusion caused a significant prolongation in central conduction time (CCT). None of these 14 patients showed any postoperative deficits.In 42 patients (30 MCA aneurysms, 12 ICA aneurysms), the SEP cortical component (N20) became flat during temporary vascular occlusion. In thirty nine of these 42 patients, the N20 peak reappeared immediately following recirculation and returned to the baseline recordings. None of these 39 patients showed postoperative neurological deficits. The length of disappearance of the N20 ranged from 2 to 38 minutes (mean of 12.3 minutes). Therefore, it is likely that the postoperative outcome can be expected to be favorable if the temporary clip is released within about 10 minutes after attenuation of the N20. The remaining three patients with ICA aneurysms whose SEP did not recover following recirculation showed postoperative morbidity. In these three patients, vascular occlusions were done at multiple sites (ie, ICA. MCA and ACA), and SEPs disappeared rapidly after temporary occlusion. Judging from this result, rapid disappearance of SEPs following temporary occlusion can be considered a danger signal.In conclusion, intraoperative SEP monitoring during temporary occlusion was useful in detecting the severity of ischemia if the vascular territory of the occluded vessel includes the sensory pathways.
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