MRI of dorsal mesencephalic lipomas.

We detected 23 intracranial lipomas using MRI. Among them were nine pericallosal lipomas, six lipomas at the dorsal surface of the midbrain, and eight in other locations. In this paper, six lipomas at the dorsal surface of the midbrain were analyzed. Five of these lipomas were in the quadrigeminal cistern and one in the left-sided quadrigeminal cistern. Excluding the smallest lipoma, five of the six lipomas had irregular margins and were broadly based on the surface of the midbrain. In these five cases, deformities of the brain parenchyma were observed adjacent to the lipomas. A mildly dilated ventricular system was observed in one of the largest lipomas in a quadrigeminal cistern. Based on their characteristic shapes and locations, we termed them "dorsal mesencephalic lipomas." Thus, the two preferential sites of intracranial lipomas were pericallosal and dorsal mesencephalic.