Dermoid sinus is sometimes also confused with dermoid cyst (a teratoma). Differential diagnosis are ectopic thyroid, enlarged lymph nodes, dermoid cysts and goiter. Mature teratomas include dermoid cysts and are generally benign. A pilonidal cyst can resemble a dermoid cyst, a kind of teratoma (germ cell tumor). Dermoid cyst symptoms are minor and the cysts are usually painless. Dermoid cysts and dysgerminomas are the most common germ cell tumors during pregnancy. Other types include cysts due to endometriosis, dermoid cysts, and cystadenomas. Other common causes of midline neck masses include lymphadenopathy, dermoid cysts, and various odontogenic anomalies. Limbal dermoid is a choristoma, not a teratoma. Skin may surround a cyst and grow abundant hair (see dermoid cyst). Due to its classification, a dermoid cyst can occur wherever a teratoma can occur. Dermoid cysts are formed from the outer layers of embryonic skin cells. Dermoid cysts are present at birth (congenital) and are common. Rarely, a dermoid cyst can develop in the vagina. Other areas where a dermoid cyst may appear are the brain, scrotum and the pharynx.