Localization of the Epileptogenic Zone Based on 3D-Reconstruction of the MRI

ABSTRACT

PURPOSE: Conventional MRI may not visualize the structural abnoramlity in large proportion of patients with intractable extratemporal lobe epilepsy. METHODS: Five patients with intractable extratemporal lobe epilepsy underwent resective surgery. Preoperatively, all patients underwent video-EEG monitoring using extracranial electrodes and MRI. Three had PET scans and four had MRS. 3D-reconstruction of the MRI was performed in all patients. Then, subdural grid electrodes were implanted on the suspected lesion in 3D-reconstructed brain; One had bitemporal depth electrodes insertion, and subdural grid electrodes implantation on bilateral frontal lobe. Two had frontal resection and including supplementary sensorimotor area in one. Parietal and parieto-temporal resection was performed in each. One had partial occipital lobe resection. RESULTS: All had complex partial seizures and four of them had lateralizing signs. Standard surface EEG recordings were not reliable in lateralizing or localizing the epileptogenic zone in any of patients. Conventional MRI revealed subtle abnormality in the superior parietal lobule, and atrophic changes in parietal lobe and posterior portion of the superior temporal gyrus, in each. Three did not show any structural abnormalities. MRS showed abnormal NAA/Ch: Cr ratio in two; one in the lesion and one in the bilateral hipocampus. PET showed hypometabolism in the extensive area in three with limitation in localizing the epileptogenic zone. All had abnormal gyral and sulcal paterns in 3D-reconstructed brain; two in the frontal lobe, superior parietal lobule, and inferior parietal and posterior portion of the superior temporal gyrus, in each, and one in the occipital lobe. Histopathologic findings revealed cortical dysplasia in all. Three were seizure free and two were class I in Engel's classification during follow-up between 4 to 24 months. CONCLUSIONS: This study suggests that in the surgical treatment of the extratemporal lobe epilepsy without prominent abnormalities in conventional MRI, 3D-reconstruction of the MRI may be of value in localizing the epileptogenic zone.