Comparative evaluation of intracranial epidermoid tumors with computed tomography and magnetic resonance imaging

The diagnosis of intracranial epidermoid tumors with computed tomography (CT) is often difficult because of indistinct margins, close proximity to the skull base, and a density similar to that of cerebrospinal fluid (CSF). Recent experience with six histologically confirmed epidermoid tumors served to emphasize the value of magnetic resonance (MR) imaging in studying these lesions. MR images were obtained using varying spin echo and inversion recovery techniques with a 0.5-tesla superconducting magnet. CT with and without enhancement had been performed in each case. In Case 1, CT showed an ill-defined left cerebellopontine angle hypodensity. MR imaging clearly showed the presence of abnormal tissue at that location. Case 2 showed a CSF density mass in the right upper posterior fossa. MR imaging of that area showed a variegated signal of a mass extending supratentorially. CT of Case 3 showed a left medial middle fossa hypodensity with an enhancing rim. MR imaging showed a clearly extraaxial mass in that location. In Case 4, a diffuse cerebellar hemispheric hypodensity was observed on CT and was clearly demarcated by MR studies. A huge lesion, thought initially to be an arachnoid cyst on CT of Case 5, was seen on MR imaging to be a large, extraventricular mass displacing the temporal lobe. Finally, CT in Case 6 was suggestive of a poorly demarcated right cerebellopontine angle lesion, which was seen on MR images to be extraaxial, displacing the brain stem. Various MR images more clearly demonstrate the extent of abnormal tissue than CT of epidermoid tumors.