Pilar sheath acanthoma
It presents as an asymptomatic, small, skin-colored papule or nodule with a central opening (comedo), most often on the head / neck, and especially the upper lip, of middle-aged to elderly people. Pilar sheath acanthomas may occur at other sites as well.
L73.9 – Follicular disorder, unspecified
254693008 – Pilar sheath acanthoma
Differential Diagnosis & Pitfalls
- 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 follicular infundibulum – Composed of pale pink cells and sometimes clear cells forming anastomosing narrow strands that run parallel to the epidermis in a 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.