Objective
Intraoperative somatosensory evoked potentials (SEPs) are widely used for the early detections of cerebral ischemia during temporary occlusive procedures of the parent vessels in aneurysm surgery. This study intended to evaluate the usefulness of median nerve SEPs during intracranial aneurysm surgery.

Method
Between September 1995 and June 1997, we monitored 42 aneurysm patients in Uijongbu St. Mary's hospital. Median nerve SEPs were detected on scalp and cervical spine during surgery. We measured latencies, amplitudes of N20 and N13 waveforms and central conduction time (CCT, N20-N13). We analyzed pre- and post-surgical radiologic findings and changes of neurologic signs.

Results
The delayed latencies, CCT, and reduced amplitudes of median nerve SEPs during intraoperative monitoring were closely related to neurological deficits after surgery.

Conclusion
Intraoperative SEPs are useful in preventing clinical neurological injury during surgery of intracranial aneurysm and in predicting which patients will have unfavourable outcomes.