eMedicine Specialties > Dermatology > Benign Neoplasms
Pilar Cyst: Differential Diagnoses & Workup
Updated: Mar 25, 2009
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Differential Diagnoses
| Acne Keloidalis Nuchae | Pilomatrixoma |
| Dermoid Cyst | Steatocystoma Multiplex |
| Epidermal Inclusion Cyst | |
| Favre-Racouchot Syndrome (Nodular Elastosis with
Cysts and Comedones) | |
| Lipomas |
Workup
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.
Procedures
- Uncomplicated pilar cysts can be extracted with ease.
- Proliferating cysts need complete excision to prevent recurrence.
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 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.
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 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
More on Pilar Cyst |
| Overview: Pilar Cyst |
 Differential Diagnoses & Workup: Pilar Cyst |
| Treatment & Medication: Pilar Cyst |
| Follow-up: Pilar Cyst |
| Multimedia: Pilar Cyst |
| References |
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References
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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].
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.
Leppard BJ, Sanderson KV, Wells RS. Hereditary trichilemmal cysts. Hereditary pilar cysts. Clin Exp Dermatol. Mar 1977;2(1):23-32. [Medline].
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].
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.
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].
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.
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].
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].
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].
Hanau D, Grosshans E. Trichilemmal cyst with intrinsic parietal sebaceous and apocrine structures. Clin Exp Dermatol. Sep 1980;5(3):351-5. [Medline].
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].
Satyaprakash AK, Sheehan DJ, Sangueza OP. Proliferating trichilemmal tumors: a review of the literature. Dermatol Surg. Sep 2007;33(9):1102-8. [Medline].
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].
Pinkus H. "Sebaceous cysts" are trichilemmal cysts. Arch Dermatol. May 1969;99(5):544-55. [Medline].
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.
Further Reading
Keywords
pilar cysts, trichilemmal cysts, scalp cysts, benign cysts, keratinizing cyst, proliferating pilar cysts, proliferating pilar tumor
