Imaging appearance of petrous apex dermoid cysts containing little or no fat.

Intracranial dermoid cysts are rare congenital lesions with typical imaging findings of well-defined fat-containing masses located along the midline and infratentorial regions. We report two rare cases of petrous apex dermoid cyst, one in the petrous apex and the other in the interdural space, with unusual imaging appearances mimicking epidermoid cysts because of the presence of little or no fat. Dermoid cysts with little or no lipid contents, as in these cases, may be radiologically misdiagnosed as epidermoid cysts. Careful evaluation of preoperative computed tomography and magnetic resonance images is necessary because the surgical approaches used for this region vary depending on the accurate location and histopathology.