Abstracts

Rationale: Corpus Callosotomy was first introduced for treatment of medically refractory epilepsy in 1940 by Van Wagenen and Herren. The surgery involves transection of the anterior two thirds of the callosum, sometimes followed by a second operation to complete the disconnection. A significant reduction in seizures has been reported with both procedures. Although corpus callosotomy is most commonly utilized for treatment of generalized seizure types, the use of this technique to assist with localization of partial foci has previously been described. At our center, select patients with epilepsy syndromes that have features of symptomatic generalized epilepsy as well as a localization related epilepsy, corpus callosotomy followed by implantation of bilateral subdural electrodes with chronic interictal and ictal recordings is considered as a diagnostic and potentially therapeutic procedure. This study aims to explore the efficacy of this procedure with regard to clinical outcome, with the secondary goal of identifying potential clinical factors which may better identify candidates for this surgical approach. Methods: A retrospective analysis of all patients undergoing corpus callosotomy with or without placement of subdural electrodes from 1996 to 2008 was performed and 24 subjects were identified who underwent corpus callosotomy. Of these, 11 had subsequent implantation of bilateral subdural electrodes. A complete review of the preoperative surgical workups, intracranial vEEG findings, surgical interventions, and patient outcomes was performed to examine the efficacy of this technique in lateralizing ictal foci in patients with medically refractory poorly lateralized epilepsy syndromes. Results: In this series, 11/24 patients underwent placement of subdural electrodes following the callosotomy procedure. 5/24 underwent complete callosotomy in a single stage procedure without invasive monitoring. The remaining 19/24 patients underwent a standard anterior two thirds disconnection. Of the 11 patients undergoing post-callosal invasive monitoring, four went on to have focal resections. Two of these patients had complete callosotomies. The surgical outcomes are: one had initial decrease in seizures of 80-90% and is currently an Engel Class III (complete callosotomy); one is deceased (complications following status epilepticus); one was Engel Class III following surgery, and now is Class II after VNS; one was seizure free for several months and is currently Engel Class III. Conclusions: Although disconnection with corpus callosotomy may allow for lateralization of foci with rapid secondary bisynchronous discharges, in this series, only 4/11 patients had focal findings resulting in resections. The absence of focal findings in the remaining patients may be related to the underlying epilepsy syndrome or may support a role for delayed monitoring following callosotomy. The degree to which post-operative outcomes were altered by the resection is unclear. These data suggest that immediate invasive monitoring may not identify these foci.