Abstracts

Intraoperative depth electrode recording (IDER) is a technique used widely to guide the extent of resection in temporal lobectomies for refractory epilepsy based on the assumption that epileptiform discharges recorded intraoperatively relate to outcome. The usefulness of IDER in surgery for temporal lobe epilepsy, however, has not been established. Patients undergoing temporal lobectomy for refractory epilepsy at the University of Maryland from 1997 to 2003 were reviewed. IDER was used to tailor temporal lobe resections in 54 consecutive patients, either with or without mesial temporal sclerosis (MTS). Following resection of temporal neocortex, a depth electrode was placed freehand into the hippocampus for a brief recording of electrical activity. This recording was followed by an initial routine resection of the mesial tissue. Recordings were then repeated using depth electrode insertions following additional resections until no further spikes were evident or no additional resection was possible. Patient outcomes were correlated with the presence or absence of spike activity. 54 patients underwent hippocampal resection with IDER. 34 (63%) patients had spikes detected. The presence of spikes prompted modification of the initial routine resection in 30 (56%) patients. Of 33 patients with spikes identified by IDER and known outcomes, 22 (67%) had Engle Class I/II outcomes 11(33%) had Class III/IV outcomes. Of 16 patients with no spikes recorded by IDER. 14 (87.5%) had Class I/II and 2 (12.5%) had Class III/IV outcomes. Although the presence of spikes detected at any point during surgery was associated with poorer seizure outcomes, this was not statistically significant. Of the 4 patients with residual spikes at the conclusion of surgery, 2 (50%) had Class III/IV outcomes whereas of 25 patients with no residual spikes, 6 (24%) had Class III/IV outcomes. The presence of residual spikes at the conclusion of resection similarly appeared to predict poorer outcome, but the correlation did not reach statistical significance. In 23 patients with MTS, the presence or absence of residual spikes was not predictive of seizure outcome. In 21 non-MTS patients, 68% (13 of 19) of those without residual spikes had Class I/II outcomes compared to 0% (0 of 2) of those with residual spikes. The absence of spikes in non-MTS patients appeared predictive of better seizure outcomes, but the trend was not statistically significant. Only the presence of MTS as evidenced by MRI was significantly predictive of good outcome ( p=0.045). The presence of spikes recorded by IDER either pre- or post- hippocampal resection tended to correlate with poorer seizure outcomes, but did not reach statistical significance. The prognostic value of IDER in the surgical management of temporal lobe epilepsy, especially in comparison to other predictive data, such as MTS, may be limited.