Lateralizing semiology predicts the seizure outcome after epilepsy surgery in the posterior cortex

Compared with temporal or frontal resections, epilepsy surgery in the posterior cortex is rarely performed, and the literature concerning clinical predictors for the postoperative seizure outcome in this particular subgroup is sparse. The data of 42 patients with lesional focal epilepsies of the parieto-occipital lobe and the occipital border of the temporal lobe were evaluated retrospectively and related to the seizure outcome 2 years after epilepsy surgery. The investigated parameters included ictal semiology, pre- and postoperative EEG and neuroimaging, histological findings and demographic data. Postoperatively, seizure-free outcome was seen in: (i) 69% of patients with lateralizing auras, but only in 28% of patients without lateralizing auras (P = 0.01); and (ii) 57% of the patients with lateralizing seizures, but only in 17% of patients without lateralizing ictal semiology (P = 0.02). None of the patients with neither lateralizing auras nor lateralizing seizures achieved freedom from seizures (P < 0.01). The proportion of lateralizing seizures (P < 0.01) and auras (P = 0.02) in the total number of recorded seizures and auras was significantly related to the probability of a favourable surgical outcome. No patient with clinical lateralizing signs to the non-lesional hemisphere but 58% without such "false" lateralization achieved freedom from seizures (P = 0.02). The following parameters also proved to be predictive for a favourable seizure outcome: (i) tumoural aetiology; and (ii) absence of epileptiform discharges in the postoperative EEG. The presence and frequency of ictal semiology lateralizing to the lesional hemisphere and the absence of lateralizing signs to the non-lesional hemisphere are highly predictive of a favourable outcome after surgical treatment of epilepsy in the posterior cortex.