Dermoid cysts are cysts that contain skin elements including squamous epithelium and dermal appendages (adnexa), such as sebaceous and sweat glands and hair.
They are discussed separately according to anatomic location:
Strictly speaking, dermoid cysts are ectodermal inclusion cysts, like epidermoid cysts except for the latter are lined solely by squamous epithelium . However, the term is often used loosely and variably depending on the body part and clinical specialty.
First, the term may refer to multiple histologies. For example, in the floor of the mouth, dermoid cysts may include all histologic types of dysontogenetic (developmental) cysts: epidermoid cysts, (true) dermoid cysts, and teratoid cysts . Since these share a similar embryonic development , they are often discussed together using "dermoid" or "dermoid/epidermoid" as umbrella terms (with teratoid cysts receiving little attention probably due to its rarity).
Second, the term may refer to different etiologies. For example, dermoid cyst has been used interchangeably with mature (benign) cystic teratomas, even though the latter connotes a neoplasm rather than a congenital sequestration-type lesion . This usage most commonly pertains to teratomas (germ cell neoplasms) in the ovaries and testes, but also can rarely apply in the head and neck .