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Pilar sheath acanthoma - Skin
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Pilar sheath acanthoma - 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
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Pilar sheath acanthoma is a benign adnexal tumor without clinically distinguishing characteristics. The process is derived from follicular epithelium.

It exists as an asymptomatic, small, skin-colored papule or nodule with a central opening (comedo), most often upon the head / neck, and especially the upper lip, of middle-aged to elderly persons. Pilar sheath acanthoma may occur at other sites as well.

Pilar sheath acanthoma was originally described as being "less mature" than dilated pore of Winer, but "more mature" than a tumor of follicular infundibulum; indeed, to some degree, all of these lesions lie upon a histologic spectrum.

Histologically, pilar sheath acanthoma consists of a lobular proliferation of benign squamous epithelium surrounding a small cystic space. The acanthotic follicular epithelium consists of banal keratinocytes with an eosinophilic basement membrane and clear cells indicative of outer root sheath differentiation.


L73.9 – Follicular disorder, unspecified

254693008 – Pilar sheath acanthoma

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Differential Diagnosis & Pitfalls

The differential diagnosis occurs chiefly under the microscope, as clinically, pilar sheath acanthoma has a nondescript appearance.
  • Dilated pore of Winer – Consists of a larger central cystic cavity with thinner and radiating strands of epithelium, as opposed to a lobular arrangement.
  • Tumor of the follicular infundibulum – Composed of pale pink cells and sometimes clear cells forming anastomosing narrow strands that run parallel to the epidermis in shallow fashion.
  • Trichofolliculoma – Secondary and tertiary small hair follicles radiate from the wall of cystic cavity, often with a central "tuft" of multiple convalescing hairs.
  • Trichilemmoma – An endophytic proliferation of basaloid and slightly squamous appearing cells derived from follicular epithelium, with rudimentary palisading, but without marked atypia or retraction artifact.
  • Inverted follicular keratosis – An endophytic variant of a seborrheic keratosis with lesser trichilemmal differentiation, lesser palisading than a trichilemmoma, and often, with squamous eddies.

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Last Updated: 01/29/2020
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Pilar sheath acanthoma - Skin
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Pilar sheath acanthoma : Smooth nodule, Smooth papule
Clinical image of Pilar sheath acanthoma
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