Teaching Case

Cafe-au-lait spots, and axillary freckling

The patient was a member of a family with known neurofibromatosis type 1. She had multiple cafe-au-lait spots, and axillary freckling. CT and MRI studies were performed several times. On the recent follow-up by MRI, a diffusion imaging protocol was added to the conventional T1 and T2-weighted sequences.

Neurofibromatosis type 1 (NF1) is primarily a disease of nerves and astrocytes, and its intracranial manifestations mainly include optic gliomas, astrocytomas, hamartomas, and neurofibromas. Its incidence is approximately 1:2000-3000. On the other hand, NF2 is a disease of coverings of the central nervous system, and its intracranial manifestations mainly include schwannomas and meningiomas. Its incidence is approximately 1:50000. In patients with neurofibromatosis, myelin vacuolization represents a characteristic histopathological change in which layers of myelin separate from each other as they spiral around the axon. These occur at the regions where myelin is dysplastic, and they are commonly seen in the cerebellar white matter, pons, midbrain, callosal splenium, and internal capsule. On MRI areas of myelin vacuolization characteristically appear as multiple nodular lesions which are hyperintense on T2-weighted images. They usually are not seen on T1-weighted images, and there is no contrast-enhancement after intravenous administration of contrast medium, and they do not cause vasogenic edema, hence no mass effect. These features distinguish regions of myelin vacuolization from a developing astrocytoma.