Localization of the epileptogenic foci in tuberous sclerosis complex: a pediatric case report

Alexander Hunold; Jens Haueisen; Banu Ahtam; Chiran Doshi; Chellamani Harini; Susana Camposano; Simon K Warfield; Patricia Ellen Grant; Yoshio Okada; Christos Papadelis

doi:10.3389/fnhum.2014.00175

Localization of the epileptogenic foci in tuberous sclerosis complex: a pediatric case report

Front Hum Neurosci. 2014 Mar 26:8:175. doi: 10.3389/fnhum.2014.00175. eCollection 2014.

Authors

Affiliations

¹ Institute of Biomedical Engineering and Informatics, Ilmenau University of Technology , Ilmenau , Germany.
² Fetal-Neonatal Neuroimaging and Developmental Science Center, Boston Children's Hospital, Harvard Medical School , Boston, MA , USA ; Department of Newborn Medicine, Boston Children's Hospital, Harvard Medical School , Boston, MA , USA.
³ Fetal-Neonatal Neuroimaging and Developmental Science Center, Boston Children's Hospital, Harvard Medical School , Boston, MA , USA ; Department of Neurology, Boston Children's Hospital, Harvard Medical School , Boston, MA , USA.
⁴ Department of Neurology, Boston Children's Hospital, Harvard Medical School , Boston, MA , USA.
⁵ Department of Radiology, Boston Children's Hospital, Harvard Medical School , Boston, MA , USA ; Computational Radiology Laboratory, Boston Children's Hospital, Harvard Medical School , Boston, MA , USA.
⁶ Fetal-Neonatal Neuroimaging and Developmental Science Center, Boston Children's Hospital, Harvard Medical School , Boston, MA , USA ; Department of Newborn Medicine, Boston Children's Hospital, Harvard Medical School , Boston, MA , USA ; Department of Radiology, Boston Children's Hospital, Harvard Medical School , Boston, MA , USA.

Abstract

Tuberous sclerosis complex (TSC) is a rare disorder of tissue growth and differentiation, characterized by benign hamartomas in the brain and other organs. Up to 90% of TSC patients develop epilepsy and 50% become medically intractable requiring resective surgery. The surgical outcome of TSC patients depends on the accurate identification of the epileptogenic zone consisting of tubers and the surrounding epileptogenic tissue. There is conflicting evidence whether the epileptogenic zone is in the tuber itself or in abnormally developed surrounding cortex. Here, we report the localization of the epileptiform activity among the many cortical tubers in a 4-year-old patient with TSC-related refractory epilepsy undergoing magnetoencephalography (MEG), electroencephalography (EEG), and diffusion tensor imaging (DTI). For MEG, we used a prototype system that offers higher spatial resolution and sensitivity compared to the conventional adult systems. The generators of interictal activity were localized using both EEG and MEG with equivalent current dipole (ECD) and minimum norm estimation (MNE) methods according to the current clinical standards. For DTI, we calculated four diffusion scalar parameters for the fibers passing through four ROIs defined: (i) at a large cortical tuber identified at the right quadrant, (ii) at the normal appearing tissue contralateral to the tuber, (iii) at the cluster formed by ECDs fitted at the peak of interictal spikes, and (iv) at the normal appearing tissue contralateral to the cluster. ECDs were consistently clustered at the vicinity of the large calcified cortical tuber. MNE and ECDs indicated epileptiform activity in the same areas. DTI analysis showed differences between the scalar values of the tracks passing through the tuber and the ECD cluster. In this illustrative case, we provide evidence from different neuroimaging modalities, which support the view that epileptiform activity may derive from abnormally developed tissue surrounding the tuber rather than the tuber itself.

Keywords: electroencephalography; epileptogenic zone; equivalent current dipole; magnetoencephalography; pediatric epilepsy; tuberous sclerosis complex.