Abstracts

The surgical management of medically intractable epilepsy (MIE) arising in the occipital lobe and the parieto-occipital and temporo-occipital regions is not well characterized in the existing literature. Reasons include the relative uncommonness of epilepsy arising in this region and the paucity of outcomes data following posterior resections. The goal of this review is to elucidate the pathological processes responsible for these epilepsies, the surgical strategies adopted and the outcomes following resection. 38 patients (age at surgery 3 months to 46 yrs, median 13 years) underwent posterior resections for MIE, at our institution, between 1994 and 2003. In 90% of these cases, non-invasive ictal electroencephalography (EEG) was localized to or predominant over one posterior quadrant. To facilitate the localization of eloquent cortex or the localization of the ictal onset zone, subdural grid electrodes (10 patients) or intra-operative electrocorticography (5 patients) were utilized. In the remaining cases, resection was tailored based on an obvious lesion on magnetic resonance imaging scans. Outcomes were categorized using the Wieser classification. In 82% of cases, abnormalities were detected by MRI scans, within and restricted to the zone of resection. Resections were restricted to the occipital lobe (12), or combined with resections of the temporal (7), parietal (5) or temporo-parietal (14) lobes, based on imaging and EEG. 22 resections were left sided, 16 were right sided. Outcomes were assessed only for the 31 patients with at least a six month follow-up. At 26 to 481 (median 108) weeks of follow up, 26 patients (84%) had no seizures or only aura (Class 1 or 2), 2 patients experienced worthwhile improvement (Class 3 or 4), while 3 had minimal or no improvement. The most common histo-pathological findings were cortical dysplasia (50%), gliosis (26% - usually related to occipital infarction) and low grade developmental neoplasms (13%). There was no unexpected procedure related morbidity in this series. Individualized surgical plans based on the MRI and localization of seizure onset can result in excellent outcomes in selected patients with posterior quadrant epilepsy. Overall, 90% of patients experienced a significant benefit from surgery. Tailored occipital resections are of value in patients with lesional epilepsy arising from the posterior quadrant. More extensive (parieto-occipito-temporal) resections, sparing the central lobe, are designed to preserve motor function in patients with less discrete disease.