Synonyms: sebaceous cysts (a misnomer as these cysts are not of sebaceous origin).

An epidermoid cyst is a cyst where the cyst sac forms from proliferation of epidermal cells within the dermis.¹
A pilar cyst occurs when the cyst sac forms from cells from the infundibulum of the hair follicles.

There are several different types of cysts. An epidermal inclusion cyst is the result of the implantation of epidermal elements in the dermis. Milia are miniature epidermoid cysts. The aetiology of these cysts remains unclear.

Epidemiology

They are extremely common and probably most people will have one over the course of a lifetime. Often they resolve spontaneously. They are said to be twice as common in men as in women and most frequent in those aged in their 20s and 30s.

Presentation

• Most often they present as a painless skin lump.
• They may present with discharge of a foul cheese-like material.
• If they become infected they are red, inflamed and painful.
• Lesions of the genitals can be painful during intercourse and cause problems with walking or wearing underwear. They can also interfere with micturition.
• Epidermoid and pilar cysts appear as firm, round, mobile, flesh-coloured to yellow or white subcutaneous nodules of variable size.
• A central pore or punctum may tether the cyst to the overlying epidermis and a thick cheesy material can sometimes be expressed.
• In people with dark skin, the cysts may also be pigmented.

Sites affected

• The sites most commonly affected are, in descending order of frequency, the face, the trunk, the neck, the extremities, and the scalp.
• Cysts of the genitals are less common and may appear as a mass in the the vulva, the clitoris, the penis, the scrotum, or the perineum. In cultures that practice female circumcision (or female genital mutilation) cysts on the vulva are common.²
• The ocular and oral mucosae can also be affected, and cysts have been reported on the palpebral conjunctivae, on the lips, on the buccal mucosa, on and under the tongue, and even on the uvula. These are not sites with hair follicles.
• Cysts may occur on the extremities. Subungual cysts can cause changes in the nails, such as onycholysis and subungual hyperkeratosis, which may be mistaken for psoriasis or onychomycosis. These cysts also produce changes in the nails (such as pincer nails) erythema, oedema, tenderness, and pain. Palmoplantar lesions represent a unique subset of epidermoid cysts.

Differential diagnosis

• A lipoma tends to be larger and is very soft.
• A neurofibroma is hard and may be multiple.
• An abscess is hot and red and may resemble an infected sebaceous cyst.
• Multiple cysts in a teenager may suggest Gardner's syndrome.

Investigations

Usually the diagnosis is clear and no investigations are required. In exceptional cases malignancy may be suspected, in which case excision and histology are required.

Associated diseases

Epidermoid cysts are a feature of Gardner's syndrome. Gardner's syndrome is an autosomal dominant condition comprising familial polyposis coli, cutaneous cysts and osteomas or other soft-tissue tumours. The cysts tend to occur at an earlier age than usual (presenting most often in early teenage years). The face may be involved but the extremities tend to be affected more than the trunk. If the syndrome is confirmed, only total colectomy will prevent malignancy from developing in the bowel.³

Simple epidermoid cysts can also run in families.

Management

• Most people with an epidermoid or pilar cyst never seek medical attention.
• If a cyst is uncomplicated then masterly inactivity should be advised. The cyst may disappear spontaneously leaving no trace. Even the most skilful excision will leave a permanent scar. Patients who present with cysts often prefer excision.
• If the cyst is red and hot it is probably infected. An antibiotic effective against staphylococci should be chosen - for example, flucloxacillin. The contents of a cyst have an offensive odour even if not infected. Infection may be mixed and, in lesions of the scalp and anogenital area, anaerobic flora are more likely.⁴
• If the cyst has ruptured, the contents can be expressed. However the cyst may well re-form.
• An inflamed but uninfected cyst may respond to intralesional injection of steroid but it is not easy to tell if an inflamed cyst is infected or not and this is not recommended.
• If the cyst is troublesome or if the patient, after counselling, is eager to have it removed, then it may be excised as a surgical procedure under the enhanced service of minor surgery.The entire cyst wall must be removed.

Excision of an epidermoid or pilar cyst

• The usual preliminaries of informed consent are assumed. Information includes the warning that the cyst may recur if all the wall is not removed.
• Appropriate aseptic precautions should be taken.
• Local anaesthetic such as 1% lidocaine with adrenaline is used (note contra-indications to use of adrenaline in certain areas). The area is infiltrated with local anaesthetic, being careful not to puncture the cyst.
• Make a careful and superficial incision over the cyst avoiding rupture of the cyst. Care should be taken to remove all the cyst wall if the cyst is ruptured.
• Toothed forceps can be used to grip the skin - a blunt dissection of adhesions allows mobilisation of the cyst and removal. A Volkmann spoon or scissors are useful for the blunt dissection.
• If the cyst is large and leaves a significant defect then a resorbable subcutaneous suture should be used to close a potential space for haematoma to form.
• The diagnosis of a epidermoid or pilar cyst is usually obvious. However, it is usually argued that excised tissue should be submitted for histology.

Complications

• Anxiety or cosmetic embarrassment.
• Infection.
• Malignant change is very rare. This may produce rapid growth, friability, and bleeding. Individual cases rather than series are reported.⁶

Prognosis

They will usually grow slowly and only need removal if causing symptoms.⁷ If incised rather than excised, recurrence is to be expected.

Document references

1. Chandrasekaran V, Parkash S, Raghuveer CV; Epidermal cysts - a clinicopathological and biochemical study. Postgrad Med J. 1980 Dec;56(662):823-7. [abstract]
2. Onuigbo WI; Vulval epidermoid cysts in the Igbos of Nigeria. Arch Dermatol. 1976 Oct;112(10):1405-6. [abstract]
3. Leppard B, Bussey HJ; Epidermoid cysts, polyposis coli and Gardner's syndrome. Br J Surg. 1975 May;62(5):387-93. [abstract]
4. Brook I; Microbiology of infected epidermal cysts. Arch Dermatol. 1989 Dec;125(12):1658-61. [abstract]
5. Baldwin HE, Berck CM, Lynfield YL; Subcutaneous nodules of the scalp: preoperative management. J Am Acad Dermatol. 1991 Nov;25(5 Pt 1):819-30. [abstract]
6. Lopez-Rios F, Rodriguez-Peralto JL, Castano E, et al; Squamous cell carcinoma arising in a cutaneous epidermal cyst: case report and literature review. Am J Dermatopathol. 1999 Apr;21(2):174-7. [abstract]
7. Hanson LJ et al; Epidermal Inclusion Cyst, eMedicine, May 2010

Acknowledgements