Colloid cysts of the third ventricle in identical twins.

A young man presented to our unit with a colloid cyst of the third ventricle. Following successful surgical treatment his parents expressed concern over the possibility of his identical twin brother having a similar cyst. After finding one other case of colloid cysts in identical twins in the world literature we arranged a magnetic resonance scan of the asymptomatic twin. We were sceptical, but much to our surprise the scan also showed a colloid cyst in the third ventricle. Familial colloid cysts of the third ventricle have been reported only rarely. This is the second account of third ventricular colloid cysts in identical twins reported in the world literature. We present case reports of the twins, discuss the world literature on familial colloid cysts and also the genetic implications.