Dermoid cyst
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A dermoid cyst, or benign cystic teratoma, also mature cystic teratoma, is a nonmalignant tumor containing a cyst lined by epidermal cells. It can contain all the elements of the dermis, including skin, hair follicles and sweat glands, and the cyst often contains sebum. The lesion may harbor hair and calcified bone or teeth. The calcification will be apparent on x-ray. On gynecologic ultrasonography the sebum appears bright. Other cell types may be present as derivatives of the ectoderm, mesoderm or endoderm.
Dermoid.Sonography.jpg
Dermoids usually occur in the ovary, often bilaterally, and account for about 25 % of all ovarian neoplasms. Mostly they are seen in the reproductive years, but they can be found in girls and women after the menopause. The size varies, and may exceed that of the ovary as such lesions are usually asymptomatic.
As a teratoma dermoid cysts belong to the group of germ cell tumors and develop from an unfertilized primordial oocyte (a totipotential cell), thus any cell type could be present in a lesion. On a rare occasion, a benign cystic teratoma is found in the brain, where they are thought to occur when embryonic nests of tissue become trapped during the closure of the neural tube.
Dermoid cysts are almost always curable by surgical removal. On a rare occasion tissue within a lesion is hormonally active (struma ovarii) or undergoes secondary malignant degeneration. Those rare tumors which are malignant usually contain squamous cell carcinoma.
Reference
Danforth's Obstetrics and Gynecology, Ninth Edition. Lippincott Williams & Wilkins. Philadelphia 2003. ISBN 0-7817-3730-3