Epidermal Inclusion Cyst 

  • Author: Linda J Hanson, MD, MA; Chief Editor: Dirk M Elston, MD   more...
 
Updated: May 6, 2010
 

Background

Epidermoid cysts represent the most common cutaneous cysts. While they may occur anywhere on the body, they occur most frequently on the face, scalp, neck, and trunk.[1]

Historically, epidermoid cysts have been referred to by various terms, including follicular infundibular cysts, epidermal cysts, and epidermal inclusion cysts. The term epidermal inclusion cyst refers specifically to an epidermoid cyst that is the result of the implantation of epidermal elements in the dermis. Because most lesions originate from the follicular infundibulum, the more general term epidermoid cyst is favored. The term sebaceous cyst should be avoided because it implies that the cyst is of sebaceous origin. Finally, the term milia refers to very small, superficial epidermoid cysts.

Epidermoid cysts are benign lesions; however, very rare cases of various associated malignancies have been reported.[2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]

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Pathophysiology

Epidermoid cysts result from the proliferation of epidermal cells within a circumscribed space of the dermis. Analysis of their lipid pattern demonstrates similarities to the epidermis. In addition, epidermoid cysts express cytokeratins 1 and 10, which are constituents of the suprabasilar layers of the epidermis. The source of this epidermis is nearly always the infundibulum of the hair follicle, as evidenced by the observation that the lining of the 2 structures is identical.[13]

Inflammation is mediated in part by the horny material contained in epidermoid cysts. Extracts of this material have been shown to be chemotactic for polymorphonucleocytes.

Studies have suggested that human papillomavirus (HPV) and exposure to ultraviolet light (UV) may play a role in the formation of epidermoid cysts.[14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25]

The manner in which carcinomas may arise within epidermoid cysts is unclear. In a series of epidermoid cysts with carcinoma, immunohistochemical results for HPV were negative, suggesting that HPV is not likely to play a role in the development in squamous cell carcinoma (SCC) in epidermoid cysts. Chronic irritation or repetitive trauma to the epithelial lining of the cyst has been suggested to play a role in malignant transformation; however, this relationship has not been established.

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Epidemiology

Mortality/Morbidity

Epidermoid cysts are usually asymptomatic; however, they may become inflamed or secondarily infected, resulting in swelling and tenderness. Rarely, malignancies, including basal cell carcinoma, Bowen disease, SCC (most common of these rarities), mycosis fungoides, and melanoma in situ, have developed in epidermoid cysts.[13]

Race

No racial predilection has been identified. Pigmentation of epidermoid cysts is common in individuals with dark skin. In a study of Indian patients with epidermoid cysts, 63% of the cysts contained melanin pigment.[26]

Sex

Epidermoid cysts are approximately twice as common in men as in women.

Age

Epidermoid cysts may occur at any age; however, they most commonly arise in the third and fourth decades of life. Small epidermoid cysts known as milia are common in the neonatal period.

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Contributor Information and Disclosures
Author

Linda J Hanson, MD, MA  Resident Physician, Department of Dermatology, State University of New York at Buffalo School of Medicine

Linda J Hanson, MD, MA is a member of the following medical societies: American Academy of Dermatology

Disclosure: Nothing to disclose.

Coauthor(s)

Nathalie C Zeitouni, MD, CM, FRCPC  Interim Chair of Dermatology, Chief, Dermatologic Surgery, Associate Professor of Dermatology, Roswell Park Cancer Institute and State University of New York at Buffalo

Nathalie C Zeitouni, MD, CM, FRCPC is a member of the following medical societies: American Academy of Cosmetic Surgery, American Academy of Dermatology, American College of Mohs Surgery, Dermatology Foundation, International Society for Dermatologic Surgery, and Royal College of Physicians and Surgeons of Canada

Disclosure: Nothing to disclose.

Specialty Editor Board

Julie C Harper, MD  Assistant Program Director, Assistant Professor, Department of Dermatology, University of Alabama at Birmingham

Julie C Harper, MD is a member of the following medical societies: American Academy of Dermatology

Disclosure: Stiefel Honoraria Speaking and teaching; Allergan Honoraria Speaking and teaching; Intendis Honoraria Speaking and teaching; Coria Honoraria Speaking and teaching; Sanofi-Aventis Honoraria Speaking and teaching

David F Butler, MD  Professor of Dermatology, Texas A&M University College of Medicine; Chair, Department of Dermatology, Director, Dermatology Residency Training Program, Scott and White Clinic, Northside Clinic

David F Butler, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, American Medical Association, American Society for Dermatologic Surgery, American Society for MOHS Surgery, Association of Military Dermatologists, and Phi Beta Kappa

Disclosure: Nothing to disclose.

Christen M Mowad, MD  Associate Professor, Department of Dermatology, Geisinger Medical Center

Christen M Mowad, MD is a member of the following medical societies: Alpha Omega Alpha, American Academy of Dermatology, and Phi Beta Kappa

Disclosure: Nothing to disclose.

Catherine M Quirk, MD  Clinical Assistant Professor, Department of Dermatology, University of Pennsylvania

Catherine M Quirk, MD is a member of the following medical societies: Alpha Omega Alpha and American Academy of Dermatology

Disclosure: Nothing to disclose.

Chief Editor

Dirk M Elston, MD  Director, Department of Dermatology, Geisinger Medical Center

Dirk M Elston, MD is a member of the following medical societies: American Academy of Dermatology

Disclosure: Nothing to disclose.

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Unusually large epidermoid cyst with a prominent punctum on the back of a patient. (Ruler is in centimeters.)
Multiple epidermoid cysts on the forehead of a patient with Gardner syndrome.
Cyst containing keratinous material (hematoxylin and eosin, original magnification X1.6).
Higher-magnification view of the cyst wall of the cyst in Media File 3 demonstrates a true epidermis with a granular layer and adjacent laminated keratinous material (hematoxylin and eosin, original magnification X20).
 
 
 
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