Dermoid cyst

Overview
A dermoid cyst is a teratoma that contains developmentally mature skin, with hair follicles and sweat glands, sometimes luxuriant clumps of long hair, and often pockets of sebum, blood, fat, bone, nails, teeth, eyes, cartilage, and thyroid tissue. Because it contains mature tissue, a dermoid cyst almost always is benign. The rare malignant dermoid cyst usually develops squamous cell carcinoma.

Some authors use the term dermoid cyst as a frank synonym for teratoma, meaning any teratoma, regardless of its histology or location. Others use it to mean any mature, cystic teratoma. These uses appear to be most common in gynecology and dermatology.

The term dermoid is sometimes used to mean dermoid cyst but this is unfortunately vague.

Location
A dermoid cyst can occur wherever a teratoma can occur.

Periorbital dermoid cysts
Dermoid cysts can also appear in young children, often near the lateral aspect of the eyebrow (right part of the right eyebrow or left part of the left eyebrow). It often has a rubbery feel. These are sometimes watched and sometimes excised. An inflammatory reaction can occur if the dermoid cyst is disrupted.

Dermoid cysts can recur if not completely excised. Sometimes, complete excision is not practical if in a dumbbell configuration where the cyst extends through a suture line in the skull.

If the dermoid cysts appear on the medial aspect, the possibility of an encephalocele becomes greater and should be considered among the differential diagnosis.

A dermoid cyst is not a pilonidal cyst
A small dermoid cyst on the head (skull sutures, and midline: sinus, nose, palate, tongue, under the tongue, etc.) or the coccyx can be difficult to distinguish from a pilonidal cyst. This is partly because both can be full of hair. A pilonidal cyst is a pilonidal sinus that is obstructed. Any teratoma near the body surface may develop a sinus or a fistula, or even a cluster of these. Such is the case of Canadian Football League linebacker Tyrone Jones, whose teratoma was discovered when he blew a tooth out of his nose.

Treatment for dermoid cyst is surgical complete removal, preferably in one piece and without any spillage of cyst contents. Marsupialization, a surgical technique often used to treat pilonidal cyst, is inappropriate for dermoid cyst due to the risk of malignancy.