Surgical Strategy of Epilepsy Arising from Parietal and Occipital Lobes

두정엽 및 후두엽 간질에 대한 수술전략

Purpose : Resection of the epileptogenic zone in the parietal and occipital lobes may be relevant although only few studies have been reported. Methods : Eight patients with parietal epilepsy and nine patients with occipital epilepsy were included for this study. Preoperatively, all had video-EEG monitoring with extracranial electrodes, MRI, 3D-surface rendering of MRI using Allegro(ISG Technologies Inc., Toronto, Canada), and PET scans. Sixteen patients underwent invasive recording with subdural grid. Eight had parietal resection including the sensory cortex in two. Seven had partial occipital resection. Two underwent total unilateral occipital lobectomy. The extent of the resection was made based mainly on the data of invasive EEG recordings, MRI, and 3D-surface rendering of MRI, not on the intraoperative electrocorticographic findings as usually done. During resection, electrocortical stimulation was performed on the motor cortex and speech area. Results : Out of eight patients with parietal epilepsy, three had sensory aura, two had gustatory aura, and two had visual aura. Six of nine patients with occipital epilepsy had visual auras. All had complex partial seizures with lateralizing signs in 15 patients. Four had quadrantopsia. One had mild right hemiparesis. Abnormality in MRI was noticed in six out of eight parietal epilepsy and in eight out of nine occipital epilepsy. 3D-surface rendering of MRI visualized volumetric abnormality with geometric spatial relationships adjacent to the normal brain, in all of parietal and occipital epilepsy. Surface EEG recording was not reliable in localizing the epileptogenic zone in any patient. The subdural grid electrodes can be implanted on the core of the structural abnormality in 3D-reconstructed brain. Ictal onset zone was localized accurately by subdural grid EEGs in 16 patients. Motor cortex in nine and sensory speech area in two were identified by electrocortical stimulation. Histopathologic findings revealed cortical dysplasia in 10 patients ; tuberous sclerosis was combined in two, hamartoma and ganglioglioma in one each, and subpial gliosis in six. Eleven patients were seizure free at follow-up of 6 months to 37 months(mean 19.7 months) after surgery. Seizures recurred in two and were unchanged in one. Six produced transient sensory loss and one developed hemiparesis and tactile agnosia. One revealed transient apraxia. Two patients with preoperative quadrantopsia developed homonymous hemianopsia. Conclusion : This study suggests that surgical treatment was relevant in parietal and occipital epilepsies with good surgical outcome, without significant neurologic sequelae. Neuroimaging studies including conventional MRI, 3Dsurface rendering of MRI were necessary in identifying the epileptogenic zone. In particular, 3D-surface rendering of MRI was very helpful in presuming the epileptogenic zone in patients with unidentifiable lesion in the conventional MRI, in planning surgical approach to lesions, and also in making a decision of the extent of the epileptogenic zone in patients with identifiable lesion in conventional MRI. Invasive EEG recording with the subdural grid electrodes helped to confirm a core of the epileptogenic zone which was revealed in 3D-surface rendered brain.