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Trichilemmal Cyst (Pilar Cyst) Workup

  • Author: Anne Elizabeth Laumann, MBChB, MRCP(UK), FAAD; Chief Editor: William D James, MD  more...
 
Updated: Apr 07, 2016
 

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

Excision and histopathologic evaluation can confirm the diagnosis. Trichilemmal cysts can usually be extracted more easily than epidermoid cysts.[2]

If a trichilemmal cyst becomes inflamed and ruptures, the cyst should be excised and submitted for histopathology in order to exclude carcinoma, particularly nodular or nodulocystic basal cell carcinomas.[12] Inflamed, ruptured cysts may have an infectious etiology. Wound culture can elucidate infection and guide therapy if necessary.[1]

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Histologic Findings

Trichilemmal cysts are surrounded by fibrous capsules 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. They often have foci of calcification.[7] In contrast, epidermoid cysts have a granular cell layer in the lining epithelium. Epidermoid cysts (nonimplantation variant) have laminated keratin, which is believed to be derived from the follicular infundibulum.[7] Note the slides below.

Pilar cyst, low power. The trichilemmal cyst is li Pilar cyst, low power. The trichilemmal cyst is lined by squamous epithelium with a granular layer (trichilemmal keratinization) and with swelling of the cells close to the cyst cavity, which is filled with homogenous keratin. Calcifications are a common feature.
Pilar cyst, medium magnification. Higher magnifica Pilar cyst, medium magnification. Higher magnification shows the stratified squamous epithelium without a granular layer and shows swelling of the cells closest to the cyst cavity.

Tricholemmal cyst keratin stains with antikeratin antibodies derived from human hair. In contrast, epidermal cyst keratin stains with human callus–derived antikeratin antibodies.[13]

Very rarely, sebaceous or apocrine differentiation occurs in a cyst wall.[14] Calcification may be seen, and a few reports have described ossification.[15, 16]

If cyst wall rupture occurs, a foreign body giant cell reaction may surround the cyst.[5, 7]  Note the slides below.

Ruptured pilar cyst. A ruptured trichilemmal cyst Ruptured pilar cyst. A ruptured trichilemmal cyst showing replacement of the squamous lining by histiocytes and rare multinucleated giant cells.
Ruptured, low power. Another ruptured trichilemmal Ruptured, low power. Another ruptured trichilemmal cyst showing replacement of the epithelial lining by granulomatous reaction with numerous cholesterol clefts and calcifications.
Ruptured, high power. Higher-power image highlight Ruptured, high power. Higher-power image highlighting the cholesterol clefts and calcifications.

Lobules of squamous epithelium in the cyst wall suggest a proliferating trichilemmal cyst.[1] Other histologic characteristics of proliferating trichilemmal cysts may include mitoses, cell atypia, and necrosis. Penetration of tumor cells through the cyst lining suggests malignancy.[2]

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Contributor Information and Disclosures
Author

Anne Elizabeth Laumann, MBChB, MRCP(UK), FAAD Professor of Dermatology, Chief of General Dermatology, Director of the Collagen Vascular Disorders Clinic, 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, Medical Dermatology Society, Society for Investigative Dermatology, Women's Dermatologic Society

Disclosure: Nothing to disclose.

Coauthor(s)

Amanda Champlain, MD Clinical Research Fellow, Department of Dermatology, Northwestern University, The Feinberg School of Medicine

Amanda Champlain, MD is a member of the following medical societies: American College of Physicians, American Medical Association

Disclosure: Nothing to disclose.

Sapna M Amin, MD, FCAP Fellow in Dermatopathology, Department of Pathology, Northwestern University, The Feinberg School of Medicine

Sapna M Amin, MD, FCAP is a member of the following medical societies: American Society for Clinical Pathology, American Society of Dermatopathology, Chicago Dermatological Society, College of American Pathologists, Texas Society of Pathologists, United States and Canadian Academy of Pathology

Disclosure: Nothing to disclose.

Specialty Editor Board

David F Butler, MD Section Chief of Dermatology, Central Texas Veterans Healthcare System; Professor of Dermatology, Texas A&M University College of Medicine; Founding Chair, Department of Dermatology, Scott and White Clinic

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

Disclosure: Nothing to disclose.

Jeffrey Meffert, MD Associate 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, Texas Dermatological Society

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, Society for Investigative Dermatology

Disclosure: Nothing to disclose.

Additional Contributors

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 Medical Association

Disclosure: Nothing to disclose.

Acknowledgements

Mohsin Ali, MBBS, FRCP, MRCP, MRCPI Consulting Staff, Department of Dermatology, Amersham General Hospital, UK

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.

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

Disclosure: Nothing to disclose.

References
  1. Thomas VD, Snavely NR, Lee KK, Swanson NA. Benign Epithelial Tumors, Hamartomas, and Hyperplasias. Goldsmith LA, Katz SI, Gilchrest BA, Paller AS, Leffell DJ, Wolff K, eds. Fitzpatrick's Dermatology in General Medicine. 8th ed. New York, NY: McGraw-Hill; 2012. 1334.

  2. James WD, Berger TG, Elston DM. Andrews’ Diseases of the Skin: Clinical Dermatology. 12th ed. Philadelphia, Pa: Saunders Elsevier; 2015. 673.

  3. 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].

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

  5. Stone MS. Cysts. Bolognia JL, Jorizzo JL, Schaffer JV, eds. Dermatology. 3rd ed. St. Louis, MO: Saunders Elsevier; 2012. 1820-21.

  6. 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].

  7. Kirkham N. Tumors and Cysts of the Epidermis. Elder DE, Elenitsas R, Johnson BL, Murphy GF, Xu X, eds. Lever's Histopathology of the Skin. 10th ed. Philadelphia, PA: Lippincott Williams & Wilkins; 2009. 801-3.

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

  9. 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. 2008 Oct. 30(5):458-61. [Medline].

  10. Melikoglu C, Eren F, Keklik B, Aslan C, Sutcu M, Zeynep Tarini E. Trichilemmal cyst of the third fingertip: a case report. Hand Surg. 2014. 19(1):131-3. [Medline].

  11. Seidenari S, Pellacani G, Nasti S, Tomasi A, Pastorino L, Ghiorzo P, et al. Hereditary trichilemmal cysts: a proposal for the assessment of diagnostic clinical criteria. Clin Genet. 2012 Oct 15. [Epub ahead of print]:[Medline].

  12. Abreu Velez AM, Brown VM, Howard MS. An inflamed trichilemmal (pilar) cyst: Not so simple?. N Am J Med Sci. 2011 Sep. 3(9):431-4. [Medline].

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

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

  15. Pusiol T, Morichetti D, Zorzi MG, Piscioli F. Ossifying trichilemmal cyst. Am J Dermpathol. Dec 2011. 33(8):867-8. [Medline].

  16. Mommers XA, Henault B, Aubriot MH, Trost O, Malka G, Zwetyenga N. Kystes trichilemmaux ossifiants multiples du cuir chevelu : un cas familial [Multiple ossifying trichilemmal cysts of the scalp: a familial case]. Rev Stomatol Chir Maxillofac. 2012 Feb. 113(1):53-6. [Medline].

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

  18. Ibrahim AE, Barikian A, Janom H, Kaddoura I. Numerous recurrent trichilemmal cysts of the scalp: differential diagnosis and surgical management. J Craniofac Surg. Mar 2012. 23(2):e164-8. [Medline].

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

 
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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.
Pilar cyst, low power. The trichilemmal cyst is lined by squamous epithelium with a granular layer (trichilemmal keratinization) and with swelling of the cells close to the cyst cavity, which is filled with homogenous keratin. Calcifications are a common feature.
Pilar cyst, medium magnification. Higher magnification shows the stratified squamous epithelium without a granular layer and shows swelling of the cells closest to the cyst cavity.
Ruptured pilar cyst. A ruptured trichilemmal cyst showing replacement of the squamous lining by histiocytes and rare multinucleated giant cells.
Ruptured, low power. Another ruptured trichilemmal cyst showing replacement of the epithelial lining by granulomatous reaction with numerous cholesterol clefts and calcifications.
Ruptured, high power. Higher-power image highlighting the cholesterol clefts and calcifications.
 
 
 
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