Multimodality imaging for improved detection of epileptogenic foci in tuberous sclerosis complex

Objective: Using interictal alpha-[C-11]methyl-L-tryptophan ([C-11]AMT) PET scan, the authors have undertaken a quantitative analysis of all tubers visible on MRI or 2-deoxy-2-[F-18]fluoro-D-glucose ([F-18]FDG) PET, to determine the relationship between [C-11]AMT uptake and epileptic activity on EEG. Background: Tuberous sclerosis complex (TSC) is an autosomal dominant disorder, often associated with cortical tubers and intractable epilepsy. The authors have shown previously that [C-11]AMT PET scans show high tracer uptake in some epileptogenic tubers and low uptake in the remaining tubers. Methods: Eighteen children, age 7 months to 16 years, were studied. Patients underwent video-EEG monitoring, PET scans of [C-11]AMT and [F-18]FDG, and T2-weighted or fluid-attenuated inversion recovery (FLAIR) MRI. [C-11]AMT uptake values were measured in 258 cortical tubers delineated with coregistered MRI or [F-18]FDG scans. Uptake ratios were calculated between the [C-11]AMT uptake in tubers and those for normal cortex (tuber/normal cortex). Using the region of epileptiform activity, the authors performed receiver operator characteristics (ROC) analysis and determined the optimal uptake ratio for detecting presumed epileptogenic tubers. Results: Tuber uptake ratios ranged from 0.6 to 2.0. Tuber uptake ratios in the epileptic lobes were higher than those in the nonepileptic lobes (p < 0.0001). All 15 patients with focal seizure activity showed one or more lesions with uptake ratio above 0.98 in the epileptic lobe. ROC analysis showed that a tuber uptake ratio of 0.98 resulted in a specificity of 0.91. Conclusions: Cortical tubers with [C-11]AMT uptake greater than or equal to normal cortex are significantly related to epileptiform activity in that lobe. Together, interictal [C-11]AMT PET and FLAIR MRI improve the detection of potentially epileptogenic tubers in patients with TSC being evaluated for epilepsy surgery.