Researchers at Stanford University and other neurological centers in the United States performed a retrospective review and analysis of the clinical presentation and neuroanatomical features of hypothalamic lesions in 100 cases of gelastic epilepsy. Age of seizure onset was 10.52 +/- 18.12 months. Preoperative brain MRI was delayed a mean of 133.2 +/- 126.7 months after reported onset of seizures. All patients had gelastic seizures; 68 had gelastic epilepsy plus other types of seizures, including partial and generalized. Four had infantile spasms. Cognitive or developmental impairment (IQ <70) occurred in 43% (28% of patients with gelastic seizures only and 50% of those with gelastic plus multiple seizure types; p=0.052). All patients had refractory seizures. Patients with gelastic seizures plus had significantly longer duration of epilepsy (p<0.001). Precocious puberty occurred in 23%. Patients with cognitive impairment and those with precocious puberty had significantly larger lesions involving the anterior and posterior hypothalamus, at the level of the mammillary bodies. 
COMMENT. Lesions causing gelastic seizures are all localized to the mammillary level of the posterior hypothalamus. The longer duration of the epilepsy determines the development of other seizure types.