Dermoid cyst with crystalline inclusions in adjacent cortex: an ultrastructural study.

Dermoids are rare tumors of the central nervous system. So far, no electron microscopic studies of these tumors have been available. We describe the histology and ultrastructure of a dermoid cyst in a patient with situs inversus and discuss the relationship of keratin and aseptic meningitis, a well-known complication. Histological examination showed an epidermal matrix with 2-4 layers, a cyst containing keratin and debris, some hairs and sebaceous glands. In some areas, chronic inflammation had destroyed the matrix of the cyst wall. Gliosis of the adjacent brain parenchyma was evident, as were eosinophilic rod-shaped crystals. Electron microscopy revealed gliosis with Rosenthal fibers in brain parenchyma adjacent to the tumor capsule. Intracellular osmiophilic, crystalline inclusions were prominent within this area. Glial cells and neuropil were spared. No gross intracellular pathology was seen.