Abstracts

Rationale: Localization of the epileptogenic zone may be challenging in patients with Tuberous Sclerosis Complex (TSC). Previous experience at our institution has identified the single largest calcified tuber as most likely to be epileptogenic. The aim of our study was to analyze whether additional features of the brain MRI could identify the epileptogenic zone in TSC patients independently of other diagnostic and surgical data.Methods: 31 children with TSC who underwent resective epilepsy surgery at Miami Children's Hospital between 1994 and 2010 were retrospectively studied. Surgical planning had been based on multimodal data with emphasis on electrophysiological investigations. MRI s were independently reevaluated by two experts blinded to all other clinical and diagnostic data. Changes typical of both TSC (tubers, calcifications and cystic lesions) and focal cortical dysplasia (increased cortical thickness, abnormal gyration, gray/white matter blurring, transmantle changes) were identified. Localization of the findings was compared with the location of the resection cavity on the postoperative MRI. We then compared the occurrence of individual MRI changes inside and outside the resection site in 23 subjects with favorable postsurgical seizure outcome, and analyzed reasons for surgical failures in 8 subjects with unfavorable outcome.Results: MRI information alone correctly localized the resection cavity in all 23 TSC patients with favorable seizure outcomes. Significant MRI features in the resection site of these subjects included: largest tuber (n=21), calcification (n=15), cystic lesions (n=2), increased cortical thickness (n=14), abnormal gyration (n=11), transmantle changes (n=7) and gray/white matter blurring in 19/21 cases (two infants had unmyelinated white matter). Increased cortical thickness and abnormal gyration occurred only in the resection site. The relation of other MRI features to the resection site was as follows: largest tubers 11/10 (ratio of subjects with the finding only in the resection site to patients with the finding also occurring outside the resection); calcifications 12/3; transmantle changes 6/1 and gray/white matter blurring 7/12. The resection site was localized correctly using MRI in five other patients with unfavorable postsurgical outcomes; all had incomplete resections of the epileptogenic zone due to overlap with eloquent cortex. The resection site was not localized using MRI in three patients with unfavorable seizure outcomes. One of these patients had overlap of the epileptogenic zone with eloquent cortex; two subjects had multifocal epileptiform activity identified by intracranial EEG.Conclusions: Thorough MRI evaluation is able to accurately localize the epileptogenic zone in a significant proportion of TSC patients. Epileptogenic regions were characterized by FCD-like changes outside cortical tubers, especially increased cortical thickness and abnormal gyration. The findings could have important practical consequences for surgical planning in patients with intractable epilepsy due to TSC. Supported by MZOFNM2005-6504 and Kontakt Program ME09042.