Randomized controlled trial of 2.5-cm versus 3.5-cm mesial temporal resection in temporal lobe epilepsy-part 1: intent-to-treat analysis

Only one prospective randomized study on the extent of mesial resection in surgery for temporal lobe epilepsy (TLE) exists. This randomized controlled trial (RCT) examines whether 3.5-cm mesial resection is leading to a better seizure outcome than a 2.5-cm resection. Three epilepsy surgery centers using similar MRI protocols, neuropsychological tests, and resection types for TLE surgery included 207 patients in a RCT with pre- and postoperative volumetrics. One hundred and four patients were randomized into a 2.5-cm resection group and 103 patients into a 3.5-cm resection group, i.e., an intended minimum resection length of 25 versus 35 mm for the hippocampus and parahippocampus. Primary outcome measure was seizure freedom Engel class I throughout the first year. The study was powered to detect a 20% difference in class I outcome. Seizure outcome was available for 207 patients, complete volumetric results for 179 patients. Outcome analysis was restricted to control of successful randomization and an intent-to-treat analysis of seizure outcome. The mean true resection volumes were significantly different for the 2.5-cm and 3.5-cm resection groups; thus, the randomization was successful. Median resection volume in the 2.5-cm group was 72.86% of initial volume and 83.44% in the 3.5-cm group. At 1 year, seizure outcome Engel class I was 74% in the 2.5-cm and 72.8% in the 3.5-cm resection group. The primary intent-to-treat analysis did not show a different seizure freedom rate for the more posteriorly reaching 3.5-cm resection group. It appears possible that not maximal volume resection but adequate volume resection leads to good seizure freedom.