Abstracts

RATIONALE: Hypothalamic Hamartomas (HH) are often associated with epilepsy characterized by gelastic seizures (GS). Dipole source localization analysis was performed on spike discharges to investigate the relationship between HH and epileptiform activity. METHODS: Eight patients with GS and HH, aged 3 to 13 years were studied. Dipole source estimations were computed for clinically detected epileptiform spike discharges in 21-channel scalp recorded EEG. Between 16 and 60 spikes were sampled in each patient, for a total 256 spikes. Estimated dipole localizations with a goodness of fit value > 85% were considered significant. RESULTS: Spikes from five patients were topographically lateralized, occurring predominantly in frontal, fronto-temporal, posterior-temporal, and occipital regions. The corresponding dipole solutions were localized to the same hemisphere, mostly in the medial aspect of frontal and temporal regions. In all of these patients, HH were deviated to the side of EEG lateralization. The remaining 3 patients showed irregular, bilaterally diffuse spike discharges. The dipoles in these patients showed wider distribution and no consistent laterality. CONCLUSIONS: The dipole source localization technique has limited applicability for this group of patients. Results could be improved by recording EEG from more electrodes with a higher signal-to-noise ratio and achieving better alignment between measured scalp electrode positions and MRI derived scalp surfaces. However, dipoles from patients with lateralized spikes were consistently localized in the vicinity of midline structures in frontal and temporal regions in the hemisphere ipsilateral to EEG lateralization. These findings suggest that epileptiform discharges are likely to originate in the HH and propagate through the midline structures, mostly in the frontal and temporal regions and to the side of HH deviation.