Third ventricular choroid plexus arteriovenous malformation simulating a colloid cyst. Case report.

A case of a cystic encapsulated arteriovenous malformation arising from the tela choroidea of the third ventricle is reported. Although the appearance of this lesion on computerized tomography scan suggested a colloid cyst by its location, it was atypical because of the non-homogeneity both before and after contrast infusion. The increased density on the unenhanced scan was due to hemosiderin pigment in the capsule wall caused by old hemorrhage. The diagnosis in this case was made by histological examination.