Abstracts

Rationale: Temporal lobe epilepsy (TLE) is one of the most common types of localization-related epilepsy. Although surgical treatment often provides significant seizure control and freedom, identifying epileptic focus can be challenging for non-lesional imaging studies patients and invasive epilepsy monitoring with intracranial electrodes remains the gold standard in determining the epileptic zone. This study aims to compare 18-fluorodeoxyglucose positron emission tomography (PET) to invasive EEG monitoring utilizing intracranial electrodes recording (ICR) in localizing the epileptogenic focus in MRI-negative TLE patientsMethods: 104 adult patients underwent ICR, PET scan, and high resolution MRI brain from 2007 to 2009 at the Barrow Neurological Institute. All patients had standard 4 set of intracranial depth wires (orbitofrontal, lateral frontal, amygdale, and hippocampal in each hemisphere) with 8 contact electrodes per wire. Patients with insufficient number of recorded seizures and those with abnormal brain MRI were excluded. We reviewed the ictal EEG localizations by ICR and preoperative PET retrospectively. Ictal localization was divided into left temporal, right temporal, bitemporal, and poorly localized. PET studies were divided based on the hypometabolism area into left temporal, right temporal, bitemporal, extratemporal, and normalResults: Out of 104 patients, a total of 42 patients had normal MRI and sufficient seizures for ictal-focus localization. All 42 patients had PET prior to ICR that showed unitemporal hypometabolism in 10 (7 left, 3 right), bitemporal hypometabolism in 8, normal in 22, and extratemporal hypometabolism in 2. PET results were compared with those of ICR and the unitemporal group showed concordant results in 9/10 patients (7 left, 2 right) and poorly localized onset in 1 patient; the bitemporal group found to have unitemporal seizure onset in 6 patients (2 left and 4 right), and poorly localized onset in 1 patient; the normal group found to have unitemporal seizure onset in 14 patients (6 left, 8 right), bitemporal seizure onset in 7 patients, and poorly localized onset in 1 patient; and the extratemporal group had left temporal onset in 1 patient and bitemporal onset in 1 patient. It is important to note that none of the patients with unitemporal seizure focus by ICR had contralateral PET findingsConclusions: Our results indicate that the sensitivity of PET scan in detecting the epileptogenic focus is considerably significant (90%) when it shows unitemporal hypometabolism. This study suggest that MRI-negative TLE patients who have unitemporal hypometabolism on PET scan may be considered for epilepsy surgery without the need for further invasive epilepsy evaluation utilizing ICR.