Ictogenesis and symptomatogenesis of gelastic seizures in hypothalamic hamartomas: an ictal SPECT study

To topographically localize the ictogenic zone within hypothalamic hamartomas (HHs) and the symptomatogenic zone for gelastic seizure (GS), we analyzed data from both interictal and ictal single photon emission computed tomography (SPECT).

Ictal SPECT was performed immediately after GS onset in 21 patients with HH (aged 2-36 years, mean 13.8 years) who underwent stereotactic radiofrequency thermocoagulation (SRT). SPECT data were statistically analyzed by means of subtraction ictal SPECT coregistered to magnetic resonance imaging (MRI) (SISCOM) and statistical parametric mapping (SPM). Topographic localization of ictal hyperperfusion areas was evaluated.

SISCOM obtained in 27 studies demonstrated ictal hyperperfusion in the HH interface zone in 16 studies of 13 patients (hot HH group). In these patients, HHs were significantly larger than those without hyperperfusion of HH in 11 studies of 8 patients (21.4 ± 10.3 vs. 12.3 ± 7.3 mm in diameter, p < 0.05, t-test). In all patients and in the hot HH group, SPM group analysis of individual differences between interictal and ictal data revealed significantly (p < 0.001) hyperperfused areas in the ipsilateral hypothalamus, mediodorsal (MD) nucleus of the thalamus and putamen, bilateral pontine tegmentum, and contralateral inferior semilunar lobule of the cerebellum. There was no hyperperfusion in the mammillothalamocingulate pathway.

The present study confirmed that ictogenesis occurs in the HH interface zone, which should accordingly be the target for SRT. We suggest that a thalamopontocerebellar circuit plays an important role for stereotypical and automatic symptomatogenesis of GS and that the hypothalamus and MD nucleus of the thalamus are potentially involved in epileptic encephalopathy.