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Proliferating pilar tumor - Skin
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Proliferating pilar tumor - Skin

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Contributors: Whitney A. High MD, JD, MEng, Noah Craft MD, PhD, Lindy P. Fox MD, Lowell A. Goldsmith MD, MPH, Michael D. Tharp MD
Other Resources UpToDate PubMed


Proliferating pilar tumor (PPT), also known as proliferating trichilemmal cyst, is a rare neoplasm, occurring most often on the scalp of elderly women.

Like a common trichilemmal cyst, PPT arises from the isthmus of the outer root sheath of the hair. Clinically, PPT is often large and may grow rapidly. Histologically, PPT manifests features of a common trichilemmal cyst, but there is also epithelial proliferation, variable cytologic atypia, and some mitotic activity.

The malignant potential of PPT is controversial. Only a small number of cases with documented invasion and metastasis have been reported. Some experts have promoted further stratification of PPT into benign, "low-grade" malignant, and "high-grade" malignant variants. There is some subjectivity in analysis, even among experienced dermatopathologists.


L72.12 – Trichilemmal cyst

254678009 – Proliferating pilar cyst

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Differential Diagnosis & Pitfalls

  • Common trichilemmal cyst – with trichilemmal epithelium, but without histologic features of proliferation
  • Epidermoid cyst – from upper third of follicle, with a granular layer and without features of proliferation
  • Pilomatricoma – a cystic structure that arises from the lower one-third of the follicle, often with matrical elements
  • Lipoma – composed of adipose tissue without epithelium
  • Metastases – common on the scalp in elderly persons; excluded by histology

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Last Updated: 12/10/2018
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Proliferating pilar tumor - Skin
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Proliferating pilar tumor : Cyst, Scalp, Smooth nodule, Tumor
Clinical image of Proliferating pilar tumor
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