Abstracts

Rationale: Despite major advances in diagnostic modalities and surgical techniques, parieto-occipital resections still represent <10% of all epilepsy surgeries. Little is known about their long-term seizure outcome. The aim of this study is to investigate the trends in longitudinal outcome and identify potential prognostic indicators in a cohort of posterior cortex epilepsy patients investigated using modern diagnostic techniques. Methods: We reviewed 57 patients who underwent a parietal, occipital, or parieto-occipital lobectomy between 1994 and 2006 (mean follow-up 3.3 yrs, range 1-12 years). Survival analysis and multivariate regression with Cox proportional hazard models were used to define patterns of seizure recurrence and identify prognostic indicators. A favorable outcome was defined as Engel Class I at last follow-up. Results: Resections were occipital in nine, parietal in 32, and parieto-occipital in 16 cases. Most were lesionectomies (48%), followed by lobectomies(33%) and multi-lobar resections(19%). Forty per cent were female, and 62% had left sided surgery. Most cases were lesional: only one patient had a normal MRI, and 39/43 (91%) of PET scans performed were abnormal. Tumor was the most common epilepsy etiology (39%), followed by malformations of cortical development (34%), encephalomalacea (20%), vascular malformation (5%), and cryptogenic (2%). At last follow-up, 38 patients (67%) were seizure-free. The estimated chance of seizure freedom was 73.1% [95% CI 67-79] at 6 postoperative months, 68.5 % [95% CI 62-75] at 1 year, 65.8% [95% CI 59-73] between 2 and 5 years, and 54.8%[95% CI 43-66] at 6 years and beyond (figure 1). Late recurrences were very rare: 75% of seizure recurrences occurred within the first 6 postoperative months. After multivariate analysis, recurrence risk factors included an epilepsy etiology other than tumor or malformation of cortical development [risk ratio (RR) 2.29 95% CI 1.27-4.25], having a lesionectomy as opposed to lobectomy or multilobar resection [RR 2.10 95% CI 1.20-3.81], ipsilateral temporal spiking on preoperative scalp EEG [RR 2.06 95% CI 1.20-3.69], and ipsilateral spiking on postoperative EEG [RR 2.70 95% CI 1.55-4.87] [Log likelihood-ratio test p-value <0.0001]. About 80% of patients in favorable prognostic categories were seizure-free at 5 years, compared to 40-50% in those with unfavorable outcome predictors. In surgical failures, seizure severity correlated with preoperative seizure frequency and postoperative EEG findings. Successful discontinuation of antiepileptic medication was correlated with disease etiology and postoperative EEG. Conclusions: These data highlight favorable long-term outcomes following PCE surgery. Limited surgical resection and diffuse baseline epileptogenicity may be important predictors of seizure recurrence.