Abstracts

Rationale: Although it has been well documented that gelastic seizures are seen most commonly in cases of hypothalamic hamartoma, this phenomenon has also been described in other cases such as temporal or frontal lobe epilepsy. Although the propagation pathway of gelastic seizures in temporal lobe pathology is not completely understood, the proposed pathway is believed to begin with ictal activation in the temporal lobe, followed by involvement of the insular cortex and limbic system, such as the amygdala, hypothalamus, and thalamus. The activation of the limbic system is believed to result in the manifestation of laughter. We describe a case of gelastic seizures in a patient with a right posteriolateral temporal lobe tumor. The results of a SPECT study performed for presurgical evaluation is described and may aid in understanding the nature of gelastic seizures when originating from the temporal lobe.Methods: A 14 year old, right handed boy of Yemen descent with a history of a low-grade posterior temporal lobe tumor and refractory gelastic seizures was evaluated with long term video EEG (LTM), as well as ictal, interictal SPECT with MRI co-registration subtraction analysis performed by a method known as Registration to Structural Images of Subtraction Ictal SPECT (RESIST). Previous MRI with and without gadolinium showed a mildly enhancing, superficial, right posteriolateral temporal lobe lesion. MR Spectroscopy was consistent with a low grade glioma. Since hyperventilation induced his typical complex partial seizures, the ictal SPECT procedure was performed following a hyperventilation-induced complex partial seizure.Results: Interictally, periodic lateralized epileptiform discharges and continuous slowing were noted at the right posterior temporal region. Ictally, ten typical complex partial seizures, in which the patient experienced sudden unexplained laughter, automatisms, and alteration of consciousness were captured. All ictal patterns originated from the right posterior temporal region. Ictal SPECT was performed at the onset of one of these seizures, which was provoked by hyperventilation. The ictal SPECT activation demonstrated hyperperfusion most extensively in the right posteriolateral temporal cortex around the tumor site, suggesting an epileptogenic focus in this region. In addition moderate to severe ictal activation was noted in the right hypothalamus. The patient underwent electrocorticography and lesionectomy, with a favorable seizure-freedom post-operative course.Conclusions: The use of SPECT in cases of hypothalamic hamartoma has been widely studied. To the best of our knowledge, there have been no documented cases of ictal SPECT analysis in gelastic seizures originating from a temporal lobe tumor. The SPECT result in this case provides evidence of hypothalamic ictal propagation in gelastic seizures when seen in temporal lobe epilepsy. The involvement of the limbic system and the hypothalamus could reflect a complex seizure network of gelastic seizures when associated with temporal lobe epilepsy.