Abstracts

Rationale: Work from our group and others have shown that a certain proportion of medically intractable epilepsy patients have an epileptogenic zone that involves the insula. Surgery of the insular region is however associated with non-negligeable risks of injury to the opercula, branches of M2 segment of the middle cerebral artery and deeper structures such as the arcuate fasciculus, internal capsule and basal ganglia . Growing evidence supports the use of gamma knife surgery (GKS) in the treatment of seizure caused by brain tumors, arteriovenous malformations, cavernous hemangiomas and hypothalamic harmatomas. We report our experience with gamma knife surgery for pharmacoresistant insular cortex epilepsy (ICE). Methods: Retrospective study of all patients with refractory ICE treated by GKS between January 2005 and January 2010. All patients underwent an extensive presurgical evaluation prior to treatment, including video-EEG monitoring, high-resolution structural MRI, ictal SPECT and neuropsychological assessments. Radiosurgical treatment was performed by using a Leksell Gamma Knife 4C (Elekta Instruments AB). Seizure frequency after treatment was assessed and compared to baseline. Results: Three cases of medically intractable ICE treated by GKS were found (2M/1F). Mean age was 48 (range 38 to 64). Marginal and maximum radiation doses delivered were 20 Gy and 40 Gy, respectively. Treatment volume ranged from 1.2 to 3.2 cc. Case 1 had nonlesional ICE proven by depth insular electrodes but only transiently improved after left posterior insulectomy (Engel 3). Complementary GKS targeting the residual superior portion of the posterior insula led to an Engel 1 outcome after a latency of 15 months (FU = 4yrs). Case 2 had refractory ICE due to a left insular cavernoma. Seizure-freedom was attained 5 months after GKS (FU = 3.5 years) though antiepileptic withdrawal was not possible. Case 3 has refractory ICE associated with a nonspecific millimetric signal abnormality over the left posterior insula. An intracranial study confirmed the insular epileptogenic zone but was complicated by transient dysphasia from contusion of the left superior temporal gyrus. Intracerebral electrodes were removed without resective surgery. GKS was performed only 5 months ago and a longer period of follow-up is required prior to assessing efficacy (outcome at one year will be available at the meeting in December 2010). None of the patients had complications after GKS. Conclusions: To our knowledge, this is the first series of GKS performed for refractory ICE. Preliminary results indicate that GKS is a safe and promising method to control insular seizures.