TEMPORAL LOBECTOMY AND INDEPENDENT BITEMPORAL INTERICTAL ACTIVITY - WHAT DEGREE OF LATERALIZATION IS SUFFICIENT

We attempted to determine whether the degree of lateralization of independent bitemporal interictal spikes and sharp waves (ISSW) is correlated with good results after temporal lobectomy. Three observers independently counted ISSW in the scalp EEGs of 59 candidates for temporal lobectomy to determine the degree of lateralization of ISSW. Interobserver correlation in percentage of lateralization was excellent (r = 0.92). Thirty-one candidates were also evaluated with depth EEG (DEEG). Operative success was graded by the number of seizures reported in the second postoperative year. There was a significant progressive decrease in the number of good operative results as the degree of lateralization of ISSW lessened (p = 0.0142). Ninety-two percent of patients with > 90% lateralization had a good surgical outcome, whereas only 50% with < 90% lateralization had a good outcome. Even when all DEEG-recorded seizures emerged from the side of the lobectomy, patients with > 90% lateralization appeared to have better outcomes than patients with < 90% lateralization. We conclude that > 90% lateralization of temporal ISSW is associated with good surgical outcome, and DEEG may not be necessary in these patients. Less than 90% lateralization is associated with poor surgical outcome and the additional information provided by DEEG may be especially useful in such patients.