Disease directory
Trichilemmal cyst
Published: September 18, 2026Updated: September 18, 2026
Important: Informational content intended for healthcare professionals. It does not replace clinical evaluation or establish a doctor-patient relationship.
Overview
- Alternative names. Trichilemmal cyst, pilar cyst, “isthmus-catagen cyst”. Headington 1976 Headington 1976
- First description. Pinkus coined the term that many “sebaceous cysts” were actually trichilemmal cysts (1969). Pinkus 1969. The proliferating trichilemmal tumor (PTT) —a neoplasm that can arise from a cyst—was described by Wilson-Jones in 1966 (as a “proliferating epidermal cyst”). Satyaprakash 2007 .
- Epidemiology. This is a common benign lesion, predominantly found on the scalp and in middle-aged to older women; it can be multiple and familial (autosomal dominant). Ramaswamy 2013 , Al Aboud 2023 , Headington 1976 .
- Codes. ICD-10: L72.11 (pilar cyst); L72.1x (tricholemmal cyst family). ICD-11: EK70.1 (trichilemmal cyst)
- Diagnostic checklist (quick)
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Clinical presentation: firm, smooth nodule/cyst, without punctum; scalp; ± multiple.
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Cutaneous ultrasound (optional): hypoechoic with enhancement and hyperechoic foci; low Doppler.
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Biopsy/excision: sample with intact wall.
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Histology: trichilemmal keratinization, without granular layer, thick capsule, ± calcification.
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IHC (if in doubt with CE/TTM): CD34 (positive in outer sheath), Ki-67/p53 (high indices suggest proliferation/malignancy).
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Rule out TTP/TTM if: rapid growth, >5 cm, ulceration, infiltration.
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