Epidermoid cyst (syn. epithelial cyst. Sebaceous cyst is a misnomer)

Latest update 16/06/09

This chapter is set out as follows:

Aetiology

A very common cyst that contains keratin and its breakdown products, surrounded by an epidermoid wall
Many result from inflammation around a pilosebaceous follicle and can therefore follow on from the more severe lesions of acne vulgaris
Some may result from deep implantation of the epidermis by a blunt penetrating injury (implantation epidermoid cysts)

Key diagnostic features

Age of presentation – most frequently affect young and middle-aged adults, rare in childhood
Distribution – commonly on the face, neck, shoulders and chest. Often multiple
Appearance
- The cyst is situated in the dermis and raises the epidermis to produce a firm elastic dome-shaped protuberance that is mobile over the deeper structures
- Tethered to the epidermis, a central keratin-filled punctum may be present
- Cysts found near the skin surface are yellow-white
- Lesions enlarge slowly and may become inflamed
Traumatic Inclusion cysts usually occur on the palmar or plantar surfaces, buttock or knee. A history of penetrating injury is not always obtained

Additional information

Gardner's syndrome is a rare autosomal dominant disorder. It is associated with multiple epidermoid cysts (usually irregularly distributed on the face, scalp and extremities), polyposis of the colon, osteomas (mainly of the skull) and fibromas

Management

Cysts can be dissected out. Any recent infection must be allowed to settle for at least six weeks before removing a cyst. An epidermoid cyst that has been frequently infected may be difficult to dissect out and may be better managed by excision
Beware of cysts that have been present from birth, or which arose in the first first few years of life as they could represent dermoid cysts. These arise in lines of fusion and are most commonly seen on the head and neck (particularly around the eyes, in the midline or on the scalp). Dermoid cysts can have deep connections, sometimes intra-cranially, and so if need to be removed the patient must be referred to an appropriate specialist. For more information refer to the chapter on dermoid cysts

	Figure 1 – Epidermoid cyst on forehead Note the central punctum
	Figure 2 – Epidermoid cyst close to eye Lesions found close to the surface are often yellow-white
	Figure 3 – Infected epidermoid cyst on the back
	Figure 4 – Epidermoid inclusion cyst