Epidermoid tumor of the cerebellopontine angle: signal loss in the contralateral cistern.

We report a case of an epidermoid tumor of the right cerebellopontine angle (CPA) in which the contralateral CPA cistern showed abnormal, low signal intensity on T2-weighted fast spin-echo MR images. Diffusion-weighted images showed the epidermoid tumor of the right CPA extending to the prepontine cistern. The cause of the abnormal signal intensity was proved to be an artifactual signal loss due to cerebrospinal fluid flow by phase-contrast MR imaging.