A case of septum pellucidum subependymoma with a subtle imaging appearance simulating a cavum septum pellucidum.

Subependymoma is a rare benign slowly growing tumor which usually appears as a well-defined lobulated entirely intraventricular mass, in the fourth or lateral ventricles. We report a case of subependymoma involving the septum pellucidum in a 28 year old female demonstrating a subtle and unusual radiological appearance. It showed very low attenuation on computed tomography, with very high signal on T2- and low signal on T1 weighted magnetic resonance images, merging with the ventricular wall, without definite focal mass. This appearance made the tumor difficult to differentiate from the cerebrospinal fluid and simulating a cavum septum pellucidum. The patient was treated by craniotomy and gross total resection of the mass.