Dermoid cyst

A dermoid cyst is a developmental cyst resulting from inclusion of embryonic epithelium at sites of embryonic fusion. Unlike epidermoid cysts, dermoid cysts contain various adnexal structures (hair, sebaceous, eccrine or apocrine glands) and, rarely, other tissues such as bone, teeth and nerves.

This chapter is set out as follows:

• Often present at birth, nearly all present before the age of five years

Distribution

• Skin - they arise in lines of fusion, predominantly on the head and neck. Peri-orbital and midline scalp lesions are the most common
• Non-cutaneous - lesions can also be intra-cranial, intra-abdominal or arise in other parts of the body

Morphology of cutaneous cysts

• Firm skin-coloured swellings
• Can be several cm in diameter
• On the scalp they are often adherent to the periosteum or form a bulging mass over the anterior fontanelle

• Untreated, dermoid cysts persist and may later grow

• They may have deep connections and so if lesions need to be excised the patient should be referred to an appropriate specialist - it is sometimes necessary to perform imaging prior to surgery to find out the extent of the lesion eg midline tumours of the face can have intra-cranial connections and those of the back intra-spinal connections