Abstracts

RATIONALE:_ Epilepsy surgery involving the parietal lobe is an uncommon procedure that may be associated with potential neurologic morbidity, and its intracranial ictal EEG findings have not been well known. We investigated the ictal EEG patterns of epilepsy originating from the parietal lobe and its adjacent areas recorded by intracranial subdural electrode arrays. METHODS: The following intracranial ictal EEG patterns from twenty patients undergone epilepsy surgery from medically intractable parietal lobe epilepsy were studied.: Anatomical ictal onset area (pure parietal [PP], combined parietal and extraparietal such as fronto-parietal, temporo-parietal, fronto-temporo-parietal, temporo-parieto-occipital [EP]); localization within the parietal lobe (lateral, mesial); extent of ictal onset zone (focal [less than four contacts], regional [more than five contacts]); the number of ictal onset zone; frequency and waveform (low voltage fast, recruiting ictal-onset spikes or sharp waves, sinusoidal rhythm in the alpha to delta range). The duration of postoperative follow-up period was 0.5-5 years. The findings between two outcome groups were compared: class I group (seizure-free) and class II to IV group (persistent seizures). RESULTS: Eight patients (40%) had ictal onset from PP (2 mesial, 6 lateral). 12 patients (60%) were seizure-free (5 from PP, 7 from EP) and 8 were with persistent seizures (3 from PP, 5 from EP). Mesial ictal onset were seen only 4 patients (3 of them were seizure-free). Statistically significant correlation with surgical outcome (p=0.028) was shown for only one variable: extent of ictal onset zone. Patients with focal onset zone (n=9) showed better outcome (eight are seizure-free), whereas those with wide ictal onset zone (not with multiple ictal onset zones or not with dispersed ictal onset) demonstrated the poorer outcome. CONCLUSIONS: Extent of individual ictal onset zone correlates with surgical outcome. Intracranial subdural EEG is helpful in predicting the surgical outcome for the parietal lobe and its adjacent lobe epilepsy.