SUMMARYObjective: Genetic loss of Tsc1/Tsc2 function in tuberous sclerosis complex (TSC) results in altered mammalian target of rapamycin (mTOR) signaling and abnormal brain development. Although earlier studies have focused on characterization of cortical tubers, in this study we sought to examine the unique cellular and molecular features of the perituberal cortex in order to better understand its contribution to epileptogenesis, cognitive dysfunction, and autism. Methods: Standard histologic and immunohistochemical labeling was used to assess structural abnormalities and cell-specific pattern of mTORC1 activation in surgically resected cortical tubers and perituberal cortex. Western blotting was performed to quantify the expression of the mTORC1 and mTORC2 biomarkers phospho-S6 (Ser235/236), phospho-S6 (Ser240/244), and phospho-Akt (Ser473), in addition to evaluating the differential expression levels of several neuronal and glial-specific proteins in tubers and peritubers, as compared to non-TSC epilepsy specimens. Results: Tubers demonstrated mild to severe disruption of cortical lamination, the presence of pS6-positive dysplastic neurons and giant cells, an overall increase in mTORC1 and a decrease in mTORC2 activity, increased axonal connectivity and growth, and hypomyelination. Perituberal cortex presented similar histologic, immunohistochemical, and molecular features; however, they were overall milder. Axonal growth was specific for TSC and was negatively correlated with deficient myelination. Significance: Our results show an extension of cellular dysplasia and dysregulated mTOR signaling in the perituberal tissue, and demonstrate for the first time aberrant connectivity in human TSC brain. This study provides new insights into the pathophysiology of neurologic dysfunction associated with TSC and supports the intrinsic epileptogenicity of normal-appearing perituberal cortex.

Object Tuberous sclerosis complex (TSC) is a multisystem autosomal dominant disorder resulting in hamartomas of several organs. Cortical tubers are the most prominent brain lesions in TSC. Treatment-resistant epilepsy often develops early in life in patients with TSC and is associated with severe intellectual and behavioral impairments. Seizures may remit following epilepsy surgery in selected cases, yet it remains unclear whether the tuber or the perituberal cortex is the source of seizure onset. In this study, the authors reviewed the onset of seizures in patients in whom depth electrodes had been placed within or adjacent to cortical tubers. Methods After obtaining institutional review board approval, the authors retrospectively reviewed data from 12 pediatric patients with multifocal TSC and treatment-resistant epilepsy who had undergone invasive intracranial electroencephalographic monitoring. Tubers were identified on postimplantation MRI, and all depth electrodes were located. Depth electrode contacts were classified visually as either tuber/perituberal cortex or nontuber/nonperituberal cortex. Board-certified clinical neurophysiologists reviewed the seizures to identify all electrodes involved in the ictal onset. Results Among 309 recorded seizures, 104 unique ictal onset patterns were identified. Of the 11 patients with electrodes recording in a tuber, 9 had seizure onsets involving the tuber. Similarly, of the 9 patients with perituberal recording electrodes, 7 had perituberal ictal onsets. Overall, there was no difference in the percentage of contacts involved in seizure onset between the tuber and perituberal cortex. In a subset of 7 patients in whom at least 1 depth electrode contact was within the tuber and 1 was in the perituberal cortex, there was no difference between the percentage of tuber and perituberal onsets. Conclusions Findings demonstrated heterogeneity in the ictal onset patterns as well as involvement of the tuber and perituberal cortex within and between patients. Although the data are limited by the restricted region(s) sampled with intracranial electrodes, they do suggest that cortical hyperexcitability in TSC may derive from the tuber or surrounding cortex.