Electroencephalography Electrode Configuration and Source Imaging

Electroencephalography (EEG) source imaging is being used more extensively in planning for surgery in case of medically intractable epilepsy. Interictal spikes, generally found in the EEG recordings of patients diagnosed with partial focal epilepsy, are fed into the inverse algorithms to estimate the current density distribution of electrical dipoles modeling the neuronal activity. The usefulness of applying EEG source analysis techniques to estimate the epileptogenic foci has been shown in multiple studies In this study, we report our pilot study in a patient with epilepsy. Methods One patient with medically intractable epilepsy was studied using a protocol approved by the Institutional Review Boards of the University of Minnesota and University of Alabama at Birmingham. Interictal spikes were observed in the pre-operative EEG recordings of the patient. The patient underwent surgical resection and was seizure free during a 3-year follow up after the surgery. Magnetic resonance imaging (MRI) images were taken preceding and following the operation. The patient underwent invasive electrocorticography (ECoG) recording before the surgery and the physician identified the seizure onset zone (SOZ) for the patient, using the ECoG recordings. Electrode location (on head) for the patient was not available, thus a generic electrode location file, which was provided by the EEG system vendor (Electrical Geodesics Inc., Eugene, OR), was used to obtain the electrode locations. The sensors were projected to patient's head using their MRI images. For configurations with other electrode numbers, the electrodes were selected in a manner to uniformly cover the whole head, trying to be as close as possible to the modified 10-20 system. Four EEG configurations (128, 96, 64, and 32 electrodes) were studied. Eighteen interictal spikes were selected from the EEG recordings and the peak time of the spikes was used to solve the inverse problem. A realistic boundary element method (BEM) model extracted from patient's MRI images was used to model the head. The BEM model assumed three layers with conductivities of 0.33 S/m, 0.0042 S/m, and 0.33 S/m corresponding to scalp, skull, and brain tissue, respectively Results I

Chronic Granulomatous Herpes Encephalitis in a Child with Clinically Intractable Epilepsy

Most patients with herpes simplex virus Type I encephalitis experience an acute, monophasic illness. Chronic encephalitis is much less common, and few late relapses are associated with intractable seizure disorders. A 10-year-old boy was admitted to our institution for intractable epilepsy as part of an evaluation for epilepsy surgery. His history was significant for herpes meningitis at age 4 months. At that time, he presented to an outside hospital with fever for three days, with acyclovir treatment beginning on day 4 of his 40-day hospital course. He later developed infantile spasms and ultimately a mixed seizure disorder. Video electroencephalogram showed a Lennox-Gastaut-type pattern with frequent right frontotemporal spikes. Imaging studies showed an abnormality in the right frontal operculum. Based on these findings, he underwent a right frontal lobectomy. Neuropathology demonstrated chronic granulomatous inflammation with focal necrosis and mineralizations. Scattered lymphocytes, microglial nodules and nonnecrotizing granulomas were present with multinucleated giant cells. Immunohistochemistry for herpes simplex virus showed focal immunoreactivity. After undergoing acyclovir therapy, he returned to baseline with decreased seizure frequency. This rare form of herpes encephalitis has only been reported in children, but the initial presentation of meningitis and the approximate 10-year-time interval in this case are unusual