Magnetic resonance imaging of the intracranial epidermoid.

Magnetic resonance imaging (MRI) was performed in five cases of intracranial epidermoid. In three of the five patients, the low-density mass on the CT scans showed as low intensity on the T 1 and high intensity on the T2 weighted images. In the two other patients, the masses with high or isodensity on CT showed as high intensity on the T 1 weighted images and as high or low intensity on the T 2 weighted images. Thus, the intensity of epidermoid on MRI correlated fairly well with the CT density, although the former was more variable. The variety of intensities on MRI reflects differences in the chemical composition of the components in the epidermoid tissue in addition to differences in the solid and liquid state of the tissue. An epidermoid could have similar MRI findings as an arachnoid cyst with regard to intensities but its irregular margin provides a useful guide for differentiation. As in other tumours, MRI is superior for evaluation of the size and the extent of the epidermoid as well as the displacement of important neurovascular structures.