MRI-validation of SEP monitoring for ischemic events during microsurgical clipping of intracranial aneurysms

ObjectiveDuring surgical clipping of intracranial aneurysms, reduction in SEP amplitude is thought to indicate cortical ischemia and subsequent neurological deficits. Since the sensitivity of SEP is questioned, we investigated SEP with respect to post-operative ischemia.MethodsIn 36 patients with 51 intracranial aneurysms, clinical evaluation and diffusion-weighted MRI (DWI) was performed before and within 24 h after surgery. During surgery, time of temporary occlusion was recorded. MRI images were reviewed for signs of ischemia.ResultsFor 43 clip applications (84%), we observed neither pathologic SEP events nor ischemia in MRI. In two cases where reduction lasted >10 min after clip release, SEP events correlated with ischemia in the MRI. Only one of the ischemic patients was symptomatic and developed a transient hemiparesis.ConclusionsWhile pathologic SEP events correlated with visible ischemia in MRI only in two cases with late SEP recovery, ischemia in MRI may have been transient or may not have reached detection threshold in the other cases, in agreement with the absence of permanent neurological deficits.SignificanceIn complex aneurysm cases, where prolonged temporary occlusion is expected, SEP should be used to detect ischemia at a reversible stage to improve the safety of aneurysm clipping.

► After aneurysm clipping, ischemia may appear in MRI without concomitant neurological deficits. ► Ischemia may appear outside the path monitored by SEP. ► SEP should be used in particular if prolonged temporary occlusion is expected.