Ictal EEG remains the prominent predictor of seizure-free outcome after temporal lobectomy in epileptic patients with normal brain MRI

PURPOSE While an abnormal pre-operative high-resolution brain MRI portends a favorable outcome in patients undergoing resective epilepsy surgery for medically intractable localization-related epilepsy (LRE), a normal MRI is less favorable. Ascertaining desirable pre-operative predictors for successful anterior temporal lobectomy (ATL) in LRE patients with a normal brain MRI is essential to better anticipate surgical outcome. METHODS Patients with LRE and normal temporal structures on MRI underwent ATL at two epilepsy centers in the southeastern US (FL and NC). Outcome was separated into those patients that were seizure free (SF), and those that were not seizure free (NSF), and those NSF were stratified in accordance with the Engel classification system. Those with a pre-operative history of clinical risk factors, unilateral anterior temporal interictal epileptiform discharges (IEDs), well localized scalp ictal EEG with rhythmic temporal theta at onset, localized PET/ictal SPECT, and Wada asymmetry with >2.5/8, were evaluated for the purpose of predicting outcome. Where appropriate, data is presented as a median (mean +/- S.D.). RESULTS Thirty-nine patients, median age 33 years, were followed up 2 years (3+/-1.2) after ATL. Overall, 22/39 (56.4%) patients were identified as SF, and 17/39 (43.6%) patients were NSF. Ictal EEG with rhythmic temporal theta at onset was the only predictive measure of seizure-free outcome (p=0.001, Fisher's exact test), and also favorably correlated with seizure reduction (p=0.0001, r(2)=0.34, multiple regression analysis). None of the other predictors examined added greater predictive value. CONCLUSIONS ATL is a favorable option for patients with LRE even when high-resolution brain MRI reveals normal temporal structures. Normal brain MRI patients with localizing pre-operative scalp ictal EEG, have better outcomes following ATL.