Hypothalamic hamartoma in a dog.

A 10-month-old female, Wire-haired Pointing Griffon dog had a hamartoma of the hypothalamus. Episodes of sudden flaccid collapse had increased in frequency and duration for 7 months. Cerebrospinal fluid pressure was normal. A flat, pedunculated mass, 2.5 X 3.0 X 0.9 cm, covered the brain stem between the pituitary gland and pons. Its 1.2-cm-diameter connection to the hypothalamus obliterated the mammillary bodies and extended to the tuber cinereum, distorting the hypothalamus and displacing the third ventricle which also divided the rostral part of the mass. The tissue of the hamartoma resembled gray matter with bullous cytoplasmic vacuolation of many neurons, spongiform change, gemistocytosis and microscopic foci of calcification.