Pilar cyst
See also in: Hair and ScalpAlerts and Notices
Synopsis
The cysts are smooth and mobile, are keratin filled, and may or may not be tender. They occur most commonly in middle-aged individuals, especially women. They may be present as solitary or multiple lesions. Pilar cysts are the most common type of cutaneous cyst of the scalp and the second most common cutaneous cyst of the head and neck (after epidermal inclusion cysts).
Rarely, these cysts form proliferating pilar tumors (more commonly called proliferating trichilemmal cysts), which are benign but may be locally aggressive or ulcerate. Malignant transformation is very rare but can lead to distant metastasis. Verrucous pilar cysts, or pilar cysts with features of human papillomavirus infection on histopathology, have also been described.
Pilar cysts may be inherited as an autosomal dominant trait with incomplete penetrance. Multiple cysts may develop in these cases. A variant of the PLCD1 gene has been shown to be associated with cyst formation in these families, and recent genetic studies suggest that a somatic mutation on the same allele (a monoallelic two-hit mechanism) is the genetic trigger for cyst development.
Codes
ICD10CM:L72.11 – Pilar cyst
SNOMEDCT:
254677004 – Trichilemmal cyst
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Differential Diagnosis & Pitfalls
- Epidermoid cyst (epidermal inclusion)
- Dermoid cyst
- Proliferating pilar tumor
- Malignant proliferating trichilemmal tumor
- Osteoma cutis
- Pilomatrixoma
- Lipoma
- Neurofibroma
- Pseudolymphoma (lymphocytoma)
- Acne keloidalis nuchae
- Favre-Racouchot syndrome
- Furuncle (if cyst is ruptured)
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Therapy
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References
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Last Reviewed:12/12/2019
Last Updated:01/20/2022
Last Updated:01/20/2022
Patient Information for Pilar cyst
Overview
Pilar (trichilemmal) cysts, sometimes referred to as wens, are common fluid-filled growths (cysts) that form from hair follicles that are most often found on the scalp. The cysts are smooth and mobile, filled with keratin (a protein component found in hair, nails, and skin), and they may or may not be tender. Pilar cysts may run in families. Rarely, these cysts may grow more extensively and form rapidly multiplying (proliferating) pilar tumors (also called proliferating trichilemmal cysts), which are non-cancerous (benign) but may grow aggressively at the cyst site. Very rarely, pilar cysts can become cancerous.Who’s At Risk
- Pilar cysts occur in 5-10% of the population.
- Pilar cysts occur most commonly in middle-aged women.
- Pilar cysts may run in families.
Signs & Symptoms
Pilar cysts are usually found on the scalp. They appear as smooth, movable bumps under the skin. There is often more than one in an area, and they may become quite large. Occasionally, they are tender to the touch.The cysts may spontaneously burst open (rupture), usually causing intense redness and irritation.
Self-Care Guidelines
None necessary.When to Seek Medical Care
See your doctor for an evaluation if you notice any growth you are unsure of or if a known pilar cyst becomes painful.Treatments
Your doctor may:- Cut into (incise) and drain the keratin and other material inside the cyst.
- Prescribe oral antibiotics if the cyst becomes infected (a rare occurrence).
- Surgically remove (excise) the cyst.
References
Bolognia, Jean L., ed. Dermatology, pp.1723-1724. New York: Mosby, 2003.
Freedberg, Irwin M., ed. Fitzpatrick's Dermatology in General Medicine. 6th ed. pp.18, 21. New York: McGraw-Hill, 2003.
Pilar cyst
See also in: Hair and Scalp