Subcortical strokes from intracranial aneurysm surgery: Implications for intraoperative neuromonitoring

Forty-five patients underwent surgery for anterior circulation aneurysms us ing intraoperative neurophysiologic monitoring at the Johns Hopkins Hospita l during 1996. There were seven intraoperative strokes. Two were cortical s trokes associated with irreversible somatosensory evoked potential (SEP) ch anges during temporary arterial occlusion. The remaining five were subcorti cal strokes, one of which was associated with transient SEP changes during temporary arterial occlusion, but the other four occurred despite normal SE Ps throughout surgery. Somatosensory evoked potential monitoring is not sen sitive for the detection of subcortical ischemia and infarction in the dist ribution of the deep perforating arterial branches during intracranial aneu rysm surgery. Although attenuation of loss of cortical SEP responses may in dicate cerebral ischemia from inadequate collateral circulation during temp orary arterial occlusion, normal SEPs can not exclude subcortical ischemia sufficient to cause significant postoperative deficits, and may therefore p rovide a false sense of security during these surgeries.