eMedicine Specialties > Dermatology > Benign Neoplasms

Epidermal Inclusion Cyst

Author: Linda J Hanson, MD, MA, Resident Physician, Department of Dermatology, State University of New York at Buffalo School of Medicine
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
Contributor Information and Disclosures

Updated: Jun 9, 2009

Introduction

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

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.

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.

Clinical

History

  • Epidermoid cysts are usually asymptomatic.
  • Discharge of a foul-smelling “cheeselike” material may be described.
  • Less frequently, the cysts can become inflamed or infected, resulting in pain and tenderness.
  • In the uncommon event of malignancy, rapid growth, friability, and bleeding may be reported.

Physical

  • Epidermoid cysts appear as flesh–colored-to-yellowish, firm, round nodules of variable size. A central pore or punctum may be present.


Unusually large epidermoid cyst with a prominent ...

Unusually large epidermoid cyst with a prominent punctum on the back of a patient. (Ruler is in centimeters.)

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Unusually large epidermoid cyst with a prominent ...

Unusually large epidermoid cyst with a prominent punctum on the back of a patient. (Ruler is in centimeters.)

  • Reportedly, epidermoid cysts are most common (in descending order of frequency) on the face, trunk, neck, extremities, and scalp. Rare cases of epidermoid cysts occurring in bone, breast, and various intracranial locations have been reported.27
  • Epidermoid cysts in the breast and genital area are not uncommon in the general population.
  • The ocular and oral mucosae can also be affected and, cysts have been reported on the palpebral conjunctivae, lips, buccal mucosa, tongue, and uvula.
  • Epidermoid cysts can manifest in various ways on the extremities. Epidermoid cysts on the distal portions of the digits may extend into the terminal phalanx. These lesions may produce changes in the nails such as pincer nails, erythema, edema, tenderness, and pain.28

Causes

Epidermoid cysts likely form by several mechanisms. They may result from the sequestration of epidermal rests during embryonic life, occlusion of the pilosebaceous unit, or traumatic or surgical implantation of epithelial elements. HPV infection, ultraviolet exposure, and eccrine duct occlusion may be additional factors in the development of palmoplantar epidermoid cysts.29 HPV has also been identified in nonpalmoplantar epidermoid cysts.

  • Congenital epidermoid cysts of the anterior fontanelle or those that are orogenital in location presumably result from sequestration or trapping of epidermal rests along embryonic fusion planes during development. Lip and lingual lesions may be related to aberrant fusion of the branchial arches, while genital lesions may result from improper closure of the genital folds.
  • Any benign or malignant process affecting or growing near the pilosebaceous unit may lead to occlusion or impingement of the follicular ostia with subsequent formation of a cyst.
    • Cysts with an acneiform distribution are likely the result of follicular occlusion.
    • In elderly persons, accumulated sun damage can injure the pilosebaceous unit, causing abnormalities such as comedonal plugging and hypercornification, both of which can eventuate in cyst formation.30 This condition is referred to as Favre-Roucouchout syndrome.
  • True epidermal inclusion cysts result from the implantation of epithelial elements in the dermis.
    • Certain injuries, especially of the crushing type, have been associated with subungual or terminal phalanx epidermoid cysts. A crush injury sustained from slamming a car door on a digit is frequently reported.
    • Any surgical procedure can theoretically result in epidermoid cysts. Reports describe the formation of multiple epidermoid cysts after rhinoplasty, breast augmentation, and liposuction.31 The use of dermal grafts, myocutaneous grafts, and needle biopsies has also been associated with the formation of epidermoid cysts.
  • Certain hereditary syndromes are associated with epidermoid cysts. Such syndromes include Gardner syndrome,32  basal cell nevus syndrome,3,10,25 and pachyonychia congenita.33,34 In addition, idiopathic scrotal calcinosis may actually represent an end stage of dystrophic calcification of epidermoid cysts.


Multiple epidermoid cysts on the forehead of a pa...

Multiple epidermoid cysts on the forehead of a patient with Gardner syndrome.

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Multiple epidermoid cysts on the forehead of a pa...

Multiple epidermoid cysts on the forehead of a patient with Gardner syndrome.

More on Epidermal Inclusion Cyst

Overview: Epidermal Inclusion Cyst
Differential Diagnoses & Workup: Epidermal Inclusion Cyst
Treatment & Medication: Epidermal Inclusion Cyst
Follow-up: Epidermal Inclusion Cyst
Multimedia: Epidermal Inclusion Cyst
References
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References

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Further Reading

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Keywords

epidermal cyst, epidermoid cyst, epithelial cyst, keratin cyst, sebaceous cyst, milia, basal cell carcinoma, Bowen's disease, SCC, mycosis fungoides, Gardner syndrome, subungual hyperkeratosis, HPV infection, seborrheic keratoses, nevi, subungual epidermoid cyst, terminal phalanx epidermoid cyst, basal cell nevus syndrome, pachyonychia congenita

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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.

Medical Editor

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

Pharmacy Editor

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.

Managing Editor

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.

CME Editor

Catherine Quirk, MD, Clinical Assistant Professor, Department of Dermatology, Brown University
Catherine 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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