Abstracts

Interhemispheric electrodes (IHE[apos]s) are increasingly used in epilepsy surgery, but the use of IHE[apos]s has been associated with heightened concern about risk of bridging vein disruption [amp] haemorrhage. We hypothesize that the use of IHE is safe and indispensable in localizing epilepsy originating from the mesial surface of the brain., We performed a retrospective review of complication rate, type of resection, EEG findings and surgical outcome of all patients who had undergone interhemispheric intracranial electrode monitoring. The interhemispheric location was anterior in 22 (69 %), and posterior in 10 (31%)., 21 patients had IHE implanted. 17 had interhemispheric grids (curvilinear-doublesided Adtech 2x8 or 3x8 grids), four had 1x8 or 1x4 strip electrodes placed interhemispherically. One patient had two interhemispheric 3x8 grids implanted. The interhemispheric location used was anterior in 22 (69 %), and posterior in 10 (31%).
Complications as a result of IHE[apos]s implantation consisted of temporary leg weakness in two patients which resolved over several days. No hemorrhagic complications or other complication related to electrode implantation were observed.
Of all the patients implanted with IHE[apos]s, 20 (95 %) underwent resective surgery, with 12 (57 %) undergoing mesial resection. Out of those 12 patients, 7 (58%) had normal MRI, while 5 (41%) had a lesion identified on MRI. In the seven patients with normal MRI, localization and resection was only possible due corticography obtained from IHE. In the remaining patients with abnormal MRI IHE determined extent of resection. Four patients had not clearly defined developmental abnormalities on MRI and in one patient with a tumor IHE clearly localized seizure onset zone. Of the 9 patients that did not localize mesially 8 (89%) underwent resection after localizing to other cortical areas. In those patients IHE were helpful in excluding mesial seizure onset. One patient (11%) did not localize and did not undergo any resection. Outcome by Engel Class for all patients that had IHE[apos]s implanted and underwent resection was: Class I- 13 (Ia-12/ Ib-1) (62 %); Class II- 3 (14 %); Class III- 2 (10 %); Class IV- 3 (14 %), Interhemispheric intracranial monitoring electrodes are a safe and effective tool in epilepsy surgery.,