[Neuroradiologic diagnosis of intracranial epidermoid tumors]

Intracranial epidermoids are primarily extracerebral congenital cysts. Intra- and extradural types are differentiated: intradural lesions originate in the intracranial CSF spaces, and extradural lesions in the bony skull. Epidermoids increase in size passively as the result of an increase in the cyst volume and not because of active growth. Clinically epidermoids behave like benign, slow-growing cerebral tumours. Differential diagnosis includes other cysts and cystic tumours. Neuroradiologically epidermoids present as polycystic lesions showing extensive growth in the extracerebral CSF spaces and secondary invagination of the brain. On CT and MR, despite the high cholesterol content, epidermoids show the characteristics of liquor and not those of fat. It can be shown that the typical CT and MR appearance of an epidermoid is due to the different proportions of CSF in the cyst content, which results from diffusion or dehiscence of the cyst capsule. The present study was based on analysis of 6 cases selected from a total of 29 patients with CNS epidermoids.