Abstracts

Rationale: FDG-PET is routinely ordered as part of the presurgical workup for children with TSC at our institution. It has been shown that epileptogenic tubers highly correlate with regions of PET hypometabolism. However, in the presurgical workup there is often high concordance between PET and other imaging and neurophysiologic localization modalities. It is unknown whether PET may uniquely identify epileptogenic foci that would not otherwise have been targeted based on EEG, MRI, ictal SPECT, dipole analysis, functional MRI, and MEG.  Methods: A database was kept of all patients with TSC who underwent stereotactic laser ablation (SLA) from 8/2010-5/2019. A retrospective chart review was performed to analyze the Phase II sEEG electrode placement, rationale for each electrode, number of electrodes placed in regions of PET hypometabolism, number of electrodes uniquely identified by PET, and electrode corridors ultimately ablated that were identified or uniquely identified by PET. This included electrodes placed into regions of PET abnormality that would not have been targeted based on data from Phase I EEG, dipole analysis, SPECT, MEG, or resting state fMRI, and were not identified as a dominant, calcified, or enhancing tuber on MRI. Results: Thirty-one patients underwent SLA for TSC at an age of 23 months to 17 years.  Of these, 29 had Phase II sEEG.  All 29 patients underwent prior Phase I EEG, MRI, and PET. In addition, 6 had dipole analysis, 23 had MEG, 20 had resting state fMRI, and 3 had ictal SPECT. 339 electrodes were placed, including 6 surface electrodes in 1 pt.  148 (43.7%) of 339 electrodes were placed in PET lesions, involving 27/29 (93.1%) of patients.  21/339 electrodes (6.2%) were targeted uniquely by PET, in 12/29 (41.4%) patients.  Of the 64 electrodes ablated, 30 (46.9%) were in PET lesions (17/29 patients), including 3 electrodes in 2/29 (6.9%) of patients that were uniquely identified by PET.Eight of the 29 patients had additional electrodes placed after an initial monitoring period, with or without ablation.  This included 10 new electrodes that had not been studied in Phase IIa, involving 4 patients. PET was not considered for the planning of any of these additional Phase IIb electrodes, and they are therefore not included in the electrode count and analysis above.  Conclusions: This study confirmed that PET contributes independently to the presurgical workup of patients with TSC. A significant portion of electrodes studied, and a similar portion of those ultimately ablated, involved regions of PET hypometabolism. PET added to the sEEG array in over 40% of patients, and led directly to the study and ultimate ablation of an epileptic focus in a small but significant number of patients (6.9%).  Funding: No funding