Evaluation with alpha-[11C]methyl-L-tryptophan positron emission tomography for reoperation after failed epilepsy surgery.

PURPOSE: Reoperation after failed cortical resection can alleviate seizures in patients with intractable neocortical epilepsy, provided that previously nonresected epileptic regions are accurately defined and removed. Most imaging modalities have limited value in identifying such regions after a previous surgery. Positron emission tomography (PET) using alpha-[11C]methyl-L-tryptophan (AMT) can detect epileptogenic cortical areas as regions with increased tracer uptake. This study analyzed whether increased cortical AMT uptake can detect nonresected epileptic foci in patients with previously failed neocortical resection.

METHODS: Thirty-three young patients (age 3-26 years; mean age, 10.8 years) with intractable epilepsy of neocortical origin, and a previously failed cortical resection performed at various epilepsy centers, underwent further presurgical evaluation for reoperation. AMT-PET scans were performed 6 days to 7 years after the first surgery. Focal cortical areas with increased AMT uptake were objectively identified and correlated to ictal EEG data as well as clinical variables (age, postsurgical time, etiology).

RESULTS: Cortical increases of AMT uptake were detected on the side of the previous resections in 12 cases. In two patients scanned shortly (within a week) after surgery, diffuse hemispheric increases were observed, without any further localization value. In contrast, in 10 (43%) of 23 patients scanned >2 months but within 2.3 years after surgery, focal cortical increases occurred, concordant with seizure onset on ictal EEG. Age, etiology (lesional vs. cryptogenic), epileptiform EEG activity during PET, or time of the last seizure were not significantly related to the presence of increased AMT uptake. All patients with localizing AMT-PET, who underwent reoperation, became seizure free (n = 5) or showed considerable improvement of seizure frequency (n = 2).

CONCLUSIONS: AMT-PET can identify nonresected epileptic cortex in patients with a previously failed neocortical epilepsy surgery and, with proper timing for the scan, can assist in planning reoperation.