Gamma Knife surgery for hypothalamic hamartomas causing refractory epilepsy: preliminary results from a prospective observational study

OBJECT: Hypothalamic hamartomas (HHs) are congenital lesions typically presenting with medically refractory epilepsy. Open or endoscopic surgical procedures to remove or disconnect the hamartoma have been reported to be effective but are associated with significant morbidity. The authors of studies on Gamma Knife surgery for HHs have reported an encouraging rate of epilepsy resolution with minimal side effects. At the Centre Hospitalier Universitaire de Sherbrooke, the authors have undertaken a prospective observational study of the outcomes of patients who underwent radiosurgery for HHs. METHODS: Patients were included in the study if they had an HH, refractory epilepsy, and no other suspected seizure focus. After radiosurgery, seizure status was assessed every 3 months and reported using the Engel Classification. Quality of life evaluation was performed annually using a standardized questionnaire, and neuropsychological evaluation was performed after 2 years. RESULTS: Nine patients were included in the study. They ranged in age from 12 to 57 years. Epilepsy began in infancy in all cases and was refractory to standard antiepileptic drugs. The patients received an average of 2 antiepileptic drugs before undergoing radiosurgery. Using the Régis Classification, 6 patients had smaller hamartomas (Grade I-III) and underwent treatment of the entire lesion, using a margin dose of 14-20 Gy. Treatment volume ranged from 0.3 to 1.0 ml. Three patients had larger lesions (Grade IV-VI) for which a radiosurgical disconnection was attempted, targeting the area of attachment to the hypothalamus. For those patients, the margin dose was 15 or 16 Gy, with treatment volume ranging from 0.8 to 1.8 ml. In all patients, the radiation dose received by the optic pathways was kept below 10 Gy. Disconnection led to no improvement in epilepsy (Engel Class IV). Four patients in whom the entire lesion was treated are now seizure free (Engel Class I), with another having only rare seizures (Engel Class II). Quality of life and verbal memory were improved in those patients with more than 3 years of follow-up. No adverse event occurred after radiosurgery. CONCLUSIONS: Radiosurgery safely and effectively controlled the epileptic disorder in patients with HHs when the entire lesion could be targeted. Radiosurgical disconnection is ineffective and cannot be recommended.

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