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Author: Megan Lam, Michael G. DeGroote School of Medicine, McMaster University, Ontario, Canada. DermNet NZ Editor in Chief: Adjunct A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. Copy edited by Gus Mitchell. April 2020.
An epidermoid cyst is a benign cyst derived from the infundibulum or upper portion of a hair follicle, encapsulated in a thin layer of epidermis-like epithelium. Epidermal cysts are typically filled with keratin and lipid-rich debris [1,2].
Synonyms for an epidermoid cyst include:
Epidermoid cysts most commonly occur in adults, particularly when young-to-middle aged. They occur twice as frequently in men than in women .
Genetic disorders which may increase the risk of developing multiple epidermoid cysts include :
Syndromes associated with epidermoid cysts
An epidermoid cyst generally results from an occluded pilosebaceous unit.
On non-hair-bearing areas of the body, such as the buttock, palm of the hand, or sole of the foot, an epidermoid cyst may be due to traumatic implantation of epidermal cells into the dermis where keratin accumulates within an epithelium-lined sac .
The clinical features of an epidermoid cyst include :
Epidermoid cysts are most common on the central trunk and face but can occur almost anywhere on the body. They are generally asymptomatic.
The rupture of the cyst contents into the dermis results in swelling, redness, and tenderness. This can be due to trauma or bacterial infection, commonly by Staphylococcus aureus, Escherichia coli, and group A streptococcus .
Cutaneous squamous cell carcinoma may very rarely arise from a cyst [5,6].
The diagnosis of an epidermoid cyst is usually made clinically.
Biopsy is usually not required but the lesion may be excised for cosmetic reasons or due to complications. Histological features of an epidermoid cyst include :
Ultrasound can be used in the initial evaluation of a soft tissue mass but is not usually required for a typical epidermoid cyst.
Differential diagnoses for an epidermoid cyst include:
Most small uncomplicated epidermoid cysts will not require treatment.
The most effective treatment for an epidermoid cyst is complete surgical excision with an intact cyst capsule. Removal of the entire cyst lining decreases rates of recurrence . This can be difficult to achieve following cyst rupture.
In cases of infection, initial incision and drainage may be indicated.
Epidermoid cysts are typically benign and slow growing, rarely undergoing malignant transformation. Occasionally, they resolve spontaneously without intervention .
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