What is a cyst?
A cyst is a lesion that contains fluid or semi-fluid material, so a cyst is fluctuant. Cutaneous cysts are harmless, sac-like growths in the deeper layers of the skin. It is not known why cysts appear. Some people get many cysts because of genetic and / or environmental influences.
What types of cyst are there?
Cutaneous cysts include:
- Epidermal cysts (with soft cheese-like and malodorous keratinous contents, often incorrectly called sebaceous cysts)
- Dermoid cysts (a developmental inclusion cyst)
- Milia (tiny surface white balls often found on the cheeks after sun exposure or following an injury).
- Trichilemmal or pilar cysts (scalp cysts with firm white content, often multiple and familial, arising from hair root sheath)
- Proliferating trichilemmal cysts (growing trichilemmal cysts)
- Steatocystomas, sometimes due to an inherited disorder, steatocystoma multiplex
- Eruptive vellus hair cysts
- Digital myxoid or mucous cyst (cyst at the base of a nail)
- Labial mucous or myxoid cyst (cyst in the lip)
- Apocrine hidrocystoma
- Sudoriferous cyst: clear jelly-like cyst of eyelid
- Bartholin cyst (vulval swelling)
- Cysts associated with pachyonychia congenita
Cysts that are not surrounded by a capsule are better known as pseudocysts. Pseudocysts include:
- Comedones (whiteheads and blackheads)
- Large uninflamed lesions arising in nodulocystic acne and hidradenitis suppurativa
- Solar comedones due to sun damage
- Pseudocyst of auricle (cyst on the external ear that follows trauma)
Multiple epidermal cysts
Large epidermal cyst
Large epidermal cyst
What are ruptured cysts?
Ruptured cysts are red, painful epidermal cysts. They may discharge yellow pus. The contents of the cyst penetrate the capsular wall and irritate the surrounding skin.
Occasionally bacteria enter the cyst and cause an infection which resembles a boil. When this happens, antibiotics, such as flucloxacillin, and minor surgery to incise the cyst and drain the pus may be needed to relieve the pressure and pain.
What is the treatment for cysts?
Small cysts (eg. less than 5 mm) don't usually need treatment, but can be readily removed by a minor surgical procedure if desired. Larger ones are usually removed because they are unsightly or because they have ruptured. It is best to avoid surgery while the cyst is actively inflamed, because surgical site infection is likely.
Cysts are treated by making a small surgical opening into the skin and removing the sac (excision biopsy). This is done under local anaesthetic and may require stitches, which are removed a few days later.
It may be difficult to extract the cyst in entirity. The cyst may then recur. Recurrence of pseudocysts is particularly common.
On DermNet NZ:
- Epidermoid cyst – pathology
- Benign keratinocytic and adnexal tumours – common skin lesions course
- Pigmented follicular cyst pathology
- Medscape Reference dermatology, the on-line textbook, has chapters on several types of cyst.
- Cysts–epidermoid and pilar – British Association of Dermatologists
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