[SEP monitoring during balloon occlusion test or operation for vertebro-basilar aneurysms]

SEP (somatosensory evoked potential) monitoring was carried out on seven patients with vertebro-basilar aneurysms during balloon occlusion test, during operation, or after operation. In the patient (case 5) with basilar tip aneurysm, the amplitude of N20 remarkably decreased and this finding closely correlated with disturbed consciousness during transient balloon occlusion of the basilar artery. In another patient (case 6) with vertebral dissecting aneurysm, cerebellar retraction caused transient prolongation of N20 latency during operation. In another case, postoperative SEP monitoring revealed marked reduction of N20 amplitude in the patient (case 7) who showed disturbed consciousness and bilateral oculomotor palsy after operation for basilar aneurysms, but who showed no abnormality in postoperative ABR (auditory evoked brainstem response). The other four patients showed no neurological deterioration and no SEP change during transient balloon occlusion of the parent arteries. Because of the high rate of "false-negative" findings, it remains unclear whether SEP monitoring during surgery for vertebrobasilar aneurysms is of value to predict postoperative deficit due to brainstem ischemia. In our study, however, the changes of SEP were well correlated with neurological deterioration and/or the location of postoperative infarction. In conclusion, SEP monitoring during balloon occlusion tests or operations for vertebro-basilar aneurysms is considered to be useful in predicting ischemic complication of the brainstem caused by the occlusion of the parent artery. However other methodologies have to be developed in order to monitor the pyramidal tract and reticular activating system of the brainstem more accurately.