Epidermoid (Mixed) Tumors of the Central Nervous System

According to their origin f rom one or more germ layers, these tumors are usually subdivided into epidermoids, 6 which contain only epidermal tissue and debris and lack dermal s t ructures; dermoids, which consist of epidermis, dermis, and dermal glands; teratoids, 2s which contain recognizable tissues of two germ layers; and tera tomas , 2~ whose characterist ic cells are derived f rom all three germ layers. I n m a n y of these complex tumors 26 der ivat ives f rom one or two germ layers tend to overgrow the others, so tha t the final analysis of the to ta l number of germ layers present n m y be difficult.