Temporary arterial occlusion during anterior communicating or anterior cerebral artery aneurysm operation under tibial nerve somatosensory evoked potential monitoring.

BACKGROUND

Median nerve somatosensory evoked potentials (SEP) have been used as an indicator of cerebral ischemia in the territory of the middle cerebral artery. This study was designed to examine whether tibial nerve SEPs are a useful technique for detecting ischemia in the territory of the anterior cerebral artery (ACA) during aneurysm surgery.

METHODS

Tibial nerve SEP monitoring was employed in 15 patients who underwent temporary arterial occlusion during surgery for aneurysms of the anterior communicating artery (ACoA) or ACA. To evaluate tibial nerve SEPs, the data after anesthesia induction but before the start of surgery were used as the control and a more than 50% decrease in the amplitude of P40-N50 was regarded as a significant change.

RESULTS

Changes in SEP were recognized in 11 of these 15 patients. Unilateral A1 occlusion resulted in SEP changes in 4/7, while bilateral A1 interruption caused changes in 6/8 of the patient group. The allowable duration of interruption of the ACA cannot be determined by A1 dominance or the extent of development of the ACoA that can be recognized by angiography. The significance of the collateral circulation via the leptomeninges was indicated. Following the release of the occlusion, SEPs were restored to the control level in all patients and no new motor deficits were found.

CONCLUSIONS

It was concluded that tibial nerve SEP monitoring is a useful system to determine the extent of cerebral ischemia of the ACA territory during temporary arterial occlusion associated with surgery for aneurysms involving the ACA system.