[Congenital epidermoid tumors of the temporal bone. 1: Pathogenesis].

Epidermoids (congenital cholesteatomas) of the mastoid air cells lying behind an intact tympanic membrane are not as rare as previously supposed. We discuss the current hypotheses of their pathogenesis critically, and favour the hypothesis of germ scattering. We summarize some not so well known details of the early stages of development of the normal involution of the first branchial cleft and of the first pharyngeal pouch as well as the subsequent development of the external meatus, the tubotympanic recess and the pneumatized spaces of the temporal bone. On this basis the transfer of ectodermal cells to the entoderm, the subsequent transmission from the embryonal closing membrane to the definite pneumatic spaces of the middle ear, and the variable frequency of recurrence of epidermoids in these diverse spaces are explained.