Arachnoid cyst of the velum interpositum.

Arachnoid cysts are thin-walled fluid-filled cavities that are uncommon causes of intracranial mass lesions [1 , 2]. These lesions have been found in various locations, both supratentorial and infratentorial [1 , 3-7] . This report describes a case in which the arachnoid cyst arose from the tela choroidea and occupied the cistern of the velum interpositum. The cyst caused symptoms similar to those seen with a third ventricular mass [8, 9] . To our knowledge, this is the first report of an arachnoid cyst in this location.