Hypothalamic hamartoma: A benign tumor of the hypothalamus, the area of the brain that controls body temperature, hunger, and thirst. (In technical terms, the hypothalamus lies beneath a structure known as the thalamus and forms the floor of the third ventricle of the brain.)
A small hypothalamic hamartoma can cause the person to feel as though they have to laugh. The tumor also causes the patient to have mild epileptic seizures. The seizures can usually be controlled with medication; the laugh cannot.
Larger hypothalamic hamartomas often cause more serious symptoms, including changes in mental ability and behavioral problems.
Patients with possible hypothalamic hamartomas should have MRI scans, which should be thoroughly scrutinized, since the growths are small and sometimes difficult to detect.