Magnetic resonance imaging of a colloid cyst of the third ventricle.

A case of an isodense non-enhancing colloid cyst of the third ventricle which was not easily diagnosed by computed tomography is described. The patient underwent magnetic resonance imaging which clearly showed a colloid cyst of the third ventricle with accompanying obstructive hydrocephalus. Such lesions are potentially life-threatening if undiagnosed. It is suggested that magnetic resonance imaging has an important role to play in rapidly and clearly demonstrating the location, size and complications of such lesions when there is doubt about the aetiology of obstructive hydrocephalus of the lateral ventricles on computed tomography.