Editor-In-Chief: C. Michael Gibson, M.S., M.D. 
Hypothalamic hamartoma (abbreviated as HH) is a congenital condition consisting of a mass of disorganized neuronal or glial tissue on or near the hypothalamus. HH is generally not detected on CT scans, and on MRI it is isointense to gray matter. The size of HHs varies from less than 1 cm to more than 3 cm. It is estimated that HH occurs in about one out of a million or two million individuals. These lesions can be pedunculated or sessile, a distinction that carries with it some differences in presenting symptoms.
The classic HH presenting syndrome is that of gelastic, or laughing, epilepsy, often mixed with other kinds of seizures; precocious puberty; and behavioral disorders. The seizures often begin when the patient is very young, although studies have shown that the onset of epilepsy can occur in adulthood. In HH, the seizures are now known to originate in the hamartoma itself, and the lesion is considered to be “intrinsically epileptogenic.” In the past, these seizures have been localized to other parts of the brain, including the temporal lobe, and sometimes resections of other brain tissue have been carried out, to poor results. Current thinking is that as the hamartoma generates constant seizures in one part of the brain, the neocortex learns to generate seizures on its own, leading to many different kinds of seizures. These seizures can have an antagonistic relationship with the characteristic behavioral disorders, which include aggressive behavior, also known as “hypothalamic rage.” Cognitive decline is often present, as manifested by poor school performance and socialization.
HH may be associated with Pallister-Hall syndrome, which is a syndrome consisting of multiple malformations, including polydactyly and imperforate anus. HH in Pallister-Hall syndrome causes less severe neurological symptoms than isolated cases of HH. Patients with isolated hamartomas often find that standard anticonvulsant treatments do not stop their seizures, leading many patients to consider surgery.
Classically, surgical resection of HH has produced poor results, with no or little reduction in seizures or behavioral disorders, and some patients have developed panhypopituitarism, which can be fatal if untreated. More recently, surgical centers such as the Barrow Neurological Institute have begun treating patients with HH, and new surgical techniques, such as the endoscopic or transcallosal approaches, have produced much better results. When these surgical techniques are used, there is often a reduction of seizure activity and behavior problems, and fewer hormonal side effects. Surgery to remove the hamartoma can also help reverse precocious puberty and the cognitive problems that affect many of the children with this disorder.
Citation: A Note on Gelastic Epilepsy. J.M.S. Pearce. European Neurology 2004;52:172-174