Pilar Cyst (Trichilemmal Cyst) Workup

  • Author: Anne Elizabeth Laumann, MBChB, MRCP(UK), FAAD; Chief Editor: William D James, MD   more...
 
Updated: Nov 8, 2011
 

Imaging Studies

  • Radiography of the head, CT scanning, and MRI may be needed to differentiate midline scalp lesions that may have a connection to the meninges or the central nervous system.
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Procedures

  • Uncomplicated pilar cysts can be extracted with ease.
  • Proliferating cysts need complete excision to prevent recurrence.
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Histologic Findings

Pilar cysts are surrounded by a fibrous capsule against which rest layers of small, cuboidal, dark-staining basal epithelial cells in a palisade arrangement with no distinct intercellular bridging. These merge with characteristic squamous epithelium composed of swollen pale keratinocytes, which increase in height as they mature and transform abruptly into solid eosinophilic-staining keratin without the formation of a granular cell layer.

The trichilemmal cyst is lined by a squamous epithThe trichilemmal cyst is lined by a squamous epithelium without a granular layer and with swelling of the cells close to the cyst cavity, which is filled with homogenous keratin. At higher magnification, the cyst is lined by a sqAt higher magnification, the cyst is lined by a squamous epithelium without a granular layer and with swelling of the cells close to the cyst cavity, which is filled with homogenous keratin.

Regardless of the age or size of the cysts, focal calcification occurs in 25% and cholesterol clefts are often present. Rupture of a cyst may lead to an intense foreign body giant cell reaction.[6]

Numerous cholesterol clefts are identified within Numerous cholesterol clefts are identified within the homogenous keratin of the trichilemmal cyst.

Very rarely, sebaceous or apocrine differentiation occurs in a cyst wall.[12]

Areas of proliferation may be found, and lobules of squamous epithelium suggest a proliferating trichilemmal cyst. Although rare, malignant transformation of a pilar cyst into a malignant proliferating trichilemmal cyst can occur.[8]

In contrast, epidermoid cysts have a granular layer in the lining epithelium. Epidermoid cysts (nonimplantation variant) have laminated keratin, which is believed to be derived from the follicular infundibulum.[6]

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Contributor Information and Disclosures
Author

Anne Elizabeth Laumann, MBChB, MRCP(UK), FAAD  Associate Professor, Department of Dermatology, Northwestern University, The Feinberg School of Medicine

Anne Elizabeth Laumann, MBChB, MRCP(UK), FAAD is a member of the following medical societies: American Academy of Dermatology, Association of Professors of Dermatology, British Association of Dermatologists, 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: Abbott Grant/research funds Other; Regeneron Grant/research funds Other; Centocor Grant/research funds Other; OSI Grant/research funds Other; Celgene Grant/research funds Other; Lilly Grant/research funds Other

Coauthor(s)

Jenneé A Rommel, MD  Resident Physician, Combined Internal Medicine/Dermatology Residency Program, Washington Hospital Center, Georgetown University School of Medicine

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.

Specialty Editor Board

R Stan Taylor, MD  The JB Howell Professor in Melanoma Education and Detection, Departments of Dermatology and Plastic Surgery, Director, Skin Surgery and Oncology Clinic, 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 Surgery, American Dermatological Association, American Medical Association, American Society for Dermatologic Surgery, Christian Medical & Dental Society, and Society for Investigative Dermatology

Disclosure: Nothing to disclose.

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.

Jeffrey Meffert, MD  Assistant Clinical Professor of Dermatology, University of Texas School of Medicine at 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.

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

William D James, MD  Paul R Gross Professor of Dermatology, Vice-Chairman, Residency Program Director, Department of Dermatology, University of Pennsylvania School of Medicine

William D James, MD is a member of the following medical societies: American Academy of Dermatology and Society for Investigative Dermatology

Disclosure: Elsevier Royalty Other

Additional Contributors

The authors and editors of Medscape Reference gratefully acknowledge the contributions of previous author, Mohsin Ali, MBBS, FRCP, MRCP, to the development and writing of this article.

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.

 
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A firm, smooth swelling on the scalp.
Surgical removal of an intact pilar cyst through an elliptical excision.
Closure of the defect after surgical removal of the pilar cyst.
The trichilemmal cyst is lined by a squamous epithelium without a granular layer and with swelling of the cells close to the cyst cavity, which is filled with homogenous keratin.
At higher magnification, the cyst is lined by a squamous epithelium without a granular layer and with swelling of the cells close to the cyst cavity, which is filled with homogenous keratin.
Numerous cholesterol clefts are identified within the homogenous keratin of the trichilemmal cyst.
 
 
 
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