Abstracts

Rationale: Surgery in frontal lobe epilepsy (FLE) has a worse prognosis regarding seizure freedom than anterior temporal lobectomy. The current study aimed to assess whether intracranial interictal and ictal EEG findings in addition to clinical and scalp EEG data help to predict outcome in a well defined series of patients with FLE surgery.Methods: Patients with FLE who had resective surgery after chronic intracranial EEG recording between 1997 and 2009 at the Jefferson Comprehensive Epilepsy Center in Philadelphia were included in this study. Predictors for outcome were compared in patients with seizure freedom (group 1) and those with recurrent seizures (group 2) at 19 to 24 months after surgery.Results: Twenty-five patients (16 females) were included in this study. Mean age of patients at epilepsy surgery was 32.3 15.6 ys (range, 12 70), mean duration of epilepsy was 16.9 13.4 ys (range, 1 48). MRI revealed frontal lobe lesions in six patients without differences between groups. Nineteen to 24 months after surgery 15 patients (60%) were seizure-free (Engel class I), 10 patients (40%) continued to have seizures (Engel II, 2 patients; Engel III, 3; and Engel IV, 5). Predictors for poor outcome were epilepsy surgery on the left (group 1, 13%; group 2, 70%; p=0.009) and on the dominant (27%; 70%; p=0.049) hemisphere as well as lack of aura (29%; 80%; p=0.036), while sex, age at surgery, duration of epilepsy, and presence of an MRI lesion in frontal lobe or extra-frontal structures were not. Electroencephalographic characteristics associated with poor outcome included the presence of interictal epileptiform discharges in scalp recordings (31%; 90%; p=0.01). Detailed analysis of intracranial EEG revealed focal (?2 cm) (88%; 30%; p=0.01) in contrast to widespread seizure onset as well as longer latency to onset of seizure spread (5.8 6.1 s; 1.5 2.3 s; p=0.019) and to ictal involvement of brain structures beyond the frontal lobe (23.5 22.4 s; 5.8 5.4 s; p=0.03) as predictors for seizure freedom. In nearly all patients the majority of interictal spikes were localized to the seizure onset zone. However, in 12 out of 25 patients, interictal epileptiform activity was seen beyond the seizure onset zone without predicting success of surgery. The distribution of ictal onset patterns was similar in both groups, and fast rhythmic activity in the beta to gamma range was found in 57% of seizure free patients compared to 70% in patients with recurrent seizures. Analysis of the temporal relation between first clinical alterations and EEG seizure onset did not reveal significant differences between both groups of patients.Conclusions: Widespread epileptogenicity as indicated by broad seizure onset zone and rapid spread of ictal activity likely explains poor outcome following focal resective surgery. The negative prognostic impact of surgery on the left and dominant hemisphere is less clear. Future study is needed to determine if neuronal network properties in these hemispheres point to intrinsic interhemispheric differences or if neurosurgeons are restrained by proximity to eloquent cortex.