eMedicine Specialties > Dermatology > Benign Neoplasms

Pilar Cyst

Author: Anne Laumann, MB, ChB, MRCP(UK), FAAD, Associate Professor, Department of Dermatology, Feinberg School of Medicine, Northwestern University
Coauthor(s): Jenneé A Rommel, MD, Clinical Research Fellow, Department of Dermatology, Feinberg School of Medicine, Northwestern University; Marjan Mirzabeigi, MD, Fellow in Dermatopathology, Department of Dermatology, Northwestern University
Contributor Information and Disclosures

Updated: Mar 25, 2009

Introduction

Background

Pilar cysts are common, occurring in 5-10% of the population.1 Greater than 90% occur on the scalp, where pilar cysts are the most common cutaneous cyst. Pilar cysts are the second most frequent type of cyst on the head and neck.2,3  Pilar cysts are almost always benign, malignant transformation being extremely rare. Pilar cysts may be sporadic or may be autosomal dominantly inherited.4 They contain keratin and its breakdown products and are lined by walls resembling the external (outer) root sheath of the hair.1

In 2% of pilar cysts, single or multiple foci of proliferating cells lead to proliferating tumors, often called proliferating trichilemmal cysts. Proliferating trichilemmal cysts grow rapidly and may also arise de novo. Although biologically benign, they may be locally aggressive, becoming large and ulcerated. Rarely, malignant transformation leads to distant metastases.5 No absolute clinical criteria can distinguish malignant from benign proliferating pilar tumors. The entire lesion must undergo histological evaluation to assess for malignancy, and atypia and a high mitotic rate are suggestive of malignancy.

Pathophysiology

Erroneously but frequently referred to as sebaceous cysts, trichilemmal cysts are derived from the outer root sheath or trichilemma of the hair follicle. The keratinization that occurs in these cysts is similar to that which occurs in the outer root sheath of the hair in the follicular isthmus, where no inner root sheath exists. The squamous epithelium undergoes rapid keratinization, resulting in a cyst wall without a granular layer.6 Trichilemmal cyst keratin stains with antikeratin antibodies derived from human hair. In contrast, epidermal cyst keratin stains with human callus–derived antikeratin antibodies.7

Pilar cysts occur preferentially in areas with dense hair follicle concentrations; therefore, 90% occur on the scalp. Pilar cysts are solitary in 30% of patients and multiple in 70% of patients.8

Frequency

United States

Pilar cysts are common, occurring in 5-10% of the population. Of people with these cysts, 70% have several and 10% have more than 10 lesions.8

Mortality/Morbidity

Pilar cysts are biologically benign, but they may be locally aggressive. Malignant transformation is very rare but may lead to distant metastases.5

Case reports have described Merkel cell carcinoma arising from Merkel cells in trichilemmal cysts.9,10

Race

Pilar cysts have no known racial predilection.

Sex

Pilar cysts are more commonly found in women than in men.8

Age

Pilar cysts are most common in persons of middle age compared with younger persons.8

Clinical

History

  • A family history may be present because the condition can have an autosomal dominant pattern of inheritance.4
  • Pilar cysts may be tender or painful if they have ruptured or become infected.

Physical

  • Pilar cysts manifest as smooth, mobile, asymptomatic swellings, often in the scalp. Overlying hair loss may be noted.3
<BR>A firm, smooth swelling on the scalp.


A firm, smooth swelling on the scalp.

[ CLOSE WINDOW ]
<BR>A firm, smooth swelling on the scalp.


A firm, smooth swelling on the scalp.

  • Unlike epidermoid cysts, no punctum is seen.
  • Multiple cysts may be present.
  • If they are inflamed, they may be tender, red, or both.
  • The contents occasionally extrude to form a soft, cutaneous horn.
  • The wall of a marsupialized cyst may fuse with the overlying epidermis to form a crypt. This may occasionally discharge its contents and then apparently spontaneously heal.

Causes

  • If the cysts are familial, the inheritance pattern is autosomal dominant. Despite attempts at gene mapping, a specific disease locus and the responsible genes are not known.11

More on Pilar Cyst

Overview: Pilar Cyst
Differential Diagnoses & Workup: Pilar Cyst
Treatment & Medication: Pilar Cyst
Follow-up: Pilar Cyst
Multimedia: Pilar Cyst
References
[ CLOSE WINDOW ]

References

  1. Casas JG, Woscoff A. Giant pilar tumor of the scalp. Arch Dermatol. Dec 1980;116(12):1395. [Medline].

  2. Al-Khateeb TH, Al-Masri NM, Al-Zoubi F. Cutaneous cysts of the head and neck. J Oral Maxillofac Surg. Jan 2009;67(1):52-7. [Medline].

  3. Wolff K, Johnson RA, Suurmond D. Miscellaneous Cysts and Pseudocysts. In: Seils A, Englis MR, eds. Fitzpatrick's Color Atlas & Synopsis of Clinical Dermatology. 5th ed. New York, NY: McGraw-Hill; 2005:200.

  4. Leppard BJ, Sanderson KV, Wells RS. Hereditary trichilemmal cysts. Hereditary pilar cysts. Clin Exp Dermatol. Mar 1977;2(1):23-32. [Medline].

  5. Weiss J, Heine M, Grimmel M, Jung EG. Malignant proliferating trichilemmal cyst. J Am Acad Dermatol. May 1995;32(5 Pt 2):870-3. [Medline].

  6. Kirkham N. Tumors and Cysts of the Epidermis. In: Elder DE, Elenitsas R, Johnson BL, Murphy GF, Xu X, eds. Lever's Histopathology of the Skin. 10th ed. Philadelphia, Pa: Lippincott Williams & Wilkins; 2004:694-7.

  7. Cotton DW, Kirkham N, Young BJ. Immunoperoxidase anti-keratin staining of epidermal and pilar cysts. Br J Dermatol. Jul 1984;111(1):63-8. [Medline].

  8. Valencia TD, Swanson NA, Lee KK. Benign Epithelial Tumors, Hamartomas, and Hyperplasias. In: Wolff K, Goldsmith LA, Katz SI, Gilchrest B, Paller AS, Leffell DJ, eds. Fitzpatrick's Dermatology in General Medicine. Vol 1. 7th ed. New York, NY: McGraw-Hill; 2008:1064-5.

  9. Ivan D, Bengana C, Lazar AJ, Diwan AH, Prieto VG. Merkel cell tumor in a trichilemmal cyst: collision or association?. Am J Dermatopathol. Apr 2007;29(2):180-3. [Medline].

  10. Su W, Kheir SM, Berberian B, Cockerell CJ. Merkel cell carcinoma in situ arising in a trichilemmal cyst: a case report and literature review. Am J Dermatopathol. Oct 2008;30(5):458-61. [Medline].

  11. Eiberg H, Hansen L, Hansen C, Mohr J, Teglbjaerg PS, Kjaer KW. Mapping of hereditary trichilemmal cyst (TRICY1) to chromosome 3p24-p21.2 and exclusion of beta-CATENIN and MLH1. Am J Med Genet A. Feb 15 2005;133A(1):44-7. [Medline].

  12. Hanau D, Grosshans E. Trichilemmal cyst with intrinsic parietal sebaceous and apocrine structures. Clin Exp Dermatol. Sep 1980;5(3):351-5. [Medline].

  13. Mehrabi D, Leonhardt JM, Brodell RT. Removal of keratinous and pilar cysts with the punch incision technique: analysis of surgical outcomes. Dermatol Surg. Aug 2002;28(8):673-7. [Medline].

  14. Satyaprakash AK, Sheehan DJ, Sangueza OP. Proliferating trichilemmal tumors: a review of the literature. Dermatol Surg. Sep 2007;33(9):1102-8. [Medline].

  15. McGavran MH, Binnington B. Keratinous cysts of the skin. Identification and differentiation of pilar cysts from epidermal cysts. Arch Dermatol. Oct 1966;94(4):499-508. [Medline].

  16. Pinkus H. "Sebaceous cysts" are trichilemmal cysts. Arch Dermatol. May 1969;99(5):544-55. [Medline].

  17. Rook A, Wilkinson DS, Ebling FJG, et al, eds. Trichilemmal cyst. In: Textbook of Dermatology. Vol 2. 6th ed. London, England: Blackwell Science; 1998:1667-8.

[ CLOSE WINDOW ]

Further Reading

[ CLOSE WINDOW ]

Keywords

pilar cysts, trichilemmal cysts, scalp cysts, benign cysts, keratinizing cyst, proliferating pilar cysts, proliferating pilar tumor

[ CLOSE WINDOW ]

Contributor Information and Disclosures

Author

Anne Laumann, MB, ChB, MRCP(UK), FAAD, Associate Professor, Department of Dermatology, Feinberg School of Medicine, Northwestern University
Anne Laumann, MB, ChB, MRCP(UK), FAAD is a member of the following medical societies: American Academy of Dermatology, Association of Professors of Dermatology, Chicago Dermatological Society, Chicago Medical Society, Illinois Dermatological Society, Illinois State Medical Society, Illinois State Medical Society, Medical Dermatology Society, and Society for Investigative Dermatology
Disclosure: Nothing to disclose.

Coauthor(s)

Jenneé A Rommel, MD, Clinical Research Fellow, Department of Dermatology, Feinberg School of Medicine, Northwestern University
Disclosure: Nothing to disclose.

Marjan Mirzabeigi, MD, Fellow in Dermatopathology, Department of Dermatology, Northwestern University
Marjan Mirzabeigi, MD is a member of the following medical societies: American Society for Clinical Pathology and College of American Pathologists
Disclosure: Nothing to disclose.

Medical Editor

R Stan Taylor, MD, Professor of Dermatology, University of Texas Southwestern Medical School; Director of Skin Surgery and Oncology Clinic, Department of Dermatology, University of Texas Southwestern Medical Center
R Stan Taylor, MD is a member of the following medical societies: American Academy of Dermatology, American College of Mohs Micrographic Surgery and Cutaneous Oncology, American Medical Association, American Society for Dermatologic Surgery, Christian Medical & Dental Society, and Society for Investigative Dermatology
Disclosure: Nothing to disclose.

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
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

Jeffrey Meffert, MD, Assistant Clinical Professor of Dermatology, University of Texas Health Science Center-San Antonio
Jeffrey Meffert, MD is a member of the following medical societies: American Academy of Dermatology, American Medical Association, Association of Military Dermatologists, and Texas Dermatological Society
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.

 
 
HONcode

We subscribe to the
HONcode principles of the
Health On the Net Foundation

All material on this website is protected by copyright, Copyright© 1994- by Medscape.
This website also contains material copyrighted by 3rd parties.

DISCLAIMER: The content of this Website is not influenced by sponsors. The site is designed primarily for use by qualified physicians and other medical professionals. The information contained herein should NOT be used as a substitute for the advice of an appropriately qualified and licensed physician or other health care provider. The information provided here is for educational and informational purposes only. In no way should it be considered as offering medical advice. Please check with a physician if you suspect you are ill.