Abstracts

Rationale: The posterior border of the temporal lobe is arbitrary and therefore the posterior border of resection in temporal lobectomy is not well defined. The Vein of Labbe is frequently used as an anatomical marker for the posterior border but it is possible that retained epileptogenic tissue behind the Vein of Labbe could affect surgical outcome. The premise of epilepsy surgery is that the complete resection of epileptogenic tissue will determine outcome and multiple physiologic modalities are used to determine the extent of epileptogenic tissue. The concordance of these modalities for determining the extent of resection in pediatric temporal lobe surgery is unknown. Methods: The records of 9 patients, ages 15 months to 17 years of age, undergoing transcortical anterior temporal lobectomy for intractable lesional epilepsy were reviewed with respect to the pre-operative surface EEG, PET data, and intraoperative ECoG. The PET CT was used when possible for intraoperative guidance with the frameless neuronavigation system (Stealth S7 system, Medtronic, Minneapolis, MN) to help guide the extent of temporal resection. Correlation between areas of hypometabolism on PET, evidence of epileptiform spikes or intraoperative seizures during ECoG, and surface EEG findings were reviewed. Results: Abnormal metabolism correlated with abnormal ECoG in four of the nine. Abnormal ECoG was present with a normal PET scan in three of the nine, and two had an abnormal PET with a normal ECoG. ECoG led to additional resection in three of the nine, two of whom were discordant for PET and ECoG. Surface EEG regionalized the seizure focus in all cases. Seven of the nine are either Engel 1 outcome at greater than one year or seizure free at less than one year follow-up. Of the two that are not seizure free, PET and ECoG were concordant in one and discordant in another.Conclusions: Abnormal PET metabolism correlates with abnormal ECoG in less than half of the cases in this small study. When discordant, abnormal ECoG with normal PET metabolism was more common than the reverse. Due to this high rate of discordance, we recommend multimodal assessment of temporal lobe dysfunction to maximize resection volume. This preliminary study lacks the statistical power to predict the impact of PET/ECoG discordance on the outcome of pediatric temporal lobe surgery, but these findings warrant ongoing study.