Abstracts

Rationale: The authors describe their experience with stereotactic implantation of insular depth electrodes in patients with medically intractable epilepsy. Methods: Between 2001 and 2009, nineteen patients with suspected insular involvement during epileptic seizures underwent intracranial electrode array implantation. All of these patients had either one or two insular depth electrodes placed as part of the intracranial array. The need for insular electrodes was determined on the basis of clinical seizure characteristics, scalp EEG findings, MRI, ictal SPECT and interictal PET scans. Results: A total of twenty-seven insular depth electrodes (12 contact, 6.5mm spacing) were placed using a frontal oblique trajectory in nineteen patients. Eleven patients had a single insular electrode placed and eight patients had two insular electrodes placed. One patient had bilateral insular electrodes placed. Post-operative imaging demonstrated satisfactory placement in all cases, and there was no associated morbidity or mortality. Thirteen patients underwent a subsequent resection, involving the frontal lobe (eight patients; three right, five left), temporal lobe (four patients; one right, three left), or fronto-temporal lobes (one patient; right). Follow-up remains preliminary (mean 15.2 months), with Engel class I in eleven patients, class III in one patient and class IV in one patient. A resectable seizure focus was not identified in the remaining six patients. Two patients (11%) had seizures originating within the insula and another six patients demonstrated early specific insular involvement. Neither patient with an insular seizure focus went on to resection. One patient with language function within the seizure onset zone underwent vagal nerve stimulator placement due to clear language participation of the insula, and the other patient declined further surgery. All six of the patients with early specific insular involvement underwent an insula-sparing resective procedure (one right frontal, three left frontal, one right temporal, one left temporal), with Engel class I outcome in all cases. Conclusions: Stereotactic placement of insular electrodes via a frontal oblique approach is a safe and efficient technique of investigating insular involvement in medically intractable epilepsy. This technique localized seizure origin within the insula in approximately 10% of cases and demonstrated early specific involvement in a further 30% of cases. Such information is valuable for appreciating the degree of insular contribution to seizures, allowing localization to the insula or clearer implication of other sites.