Results of surgery in patients with refractory extratemporal epilepsy withnormal or nonlocalizing magnetic resonance findings investigated with subdural grids

Purpose: To study the efficacy of extensive coverage of the brain surface w ith subdural grids in defining extratemporal cortical areas amenable for re section in patients with refractory extratemporal epilepy (R-ExTE) and norm al or nonlocalizing magnetic resonance imaging (MRI) scans. Methods: Sixteen patients with R-ExTE were studied. Eleven patients had sim ple partial, eight had complex partial, and three had supplementary motor a rea seizures. Seizure frequency ranged from three per month to daily episod es. Interictal EEG showed large focal spiking areas in 11 patients, seconda ry bilateral synchrony in four, and was normal in one patient. Surface icta l recordings were nonlocalizing in six patients, and in 10, they disclosed large ictal focal spiking areas. MRI was normal in 10 patients, and in six patients, focal nonlocalizing potentially epileptogenic lesions were found. All patients were given an extensive coverage of the cortical convexity wi th subdural electrodes through large unilateral (n = 13) or bilateral (n = 3) craniotomies. Bipolar cortical stimulation was carried out through the i mplanted electrodes. Results: Interictal invasive recording findings showed widespread spiking a reas in 13 patients and secondary bilateral synchrony in three. Ictal invas ive recordings showed focal seizure onset in all patients. There were six f rontal, two parietal, one temporooccipital, four rolandic, and three poster ior quadrant resections. Thirteen-patients had been rendered seizure free a fter surgery, and three had greater than or equal to 90% of seizure-frequen cy reduction. Pathologic findings included gliosis (n = 10), cortical dyspl asia (n = 5), or no abnormalities (n = 1). Six patients had transient posto perative neurologic morbidity. Conclusions: Extensive subdural electrodes coverage seems to be an effectiv e way to investigate patients with R-ExTE and normal or nonlocalizing TMRI findings.