Within the central cystic structure (comedo), a hair shaft and keratin flakes are seen. The lining of the central follicle often has a prominent granular layer.
Smaller secondary hair follicles, some of which have well-developed sebacecous glands (left center), radiate from the central follicle. The caput medusa-like architecture of this hamartomatous lesion is best seen on low power.
Trichofolliculoma is considered a hamartoma of hair follicle components. They are benign and typically occurring on the face of adults. The typical clinical appearance is that of a flesh-colored or whitish nodule on the face (Fletcher, Howard).
Histologically, there is central cystically-dilated follicle filled with keratin flakes ("comedo"). From this central cavity, there are numerous secondary hair follicles with vellus hairs that bud off, creating a "caput medusa" appearance. The central cystic follicle is usually connected to the epidermis. A rare variant of trichofolliculoma is a sebaceous trichofolliculoma in which there are well-developed sebaceous glands surrounding the central comedo cavity (Rapini, Alsaad).
Simple excision (done for cosmetic reasons) is curative.
Alsaad KO, et al. Skin adnexal neoplasms - part 1: An approach to tumors of the pilosebaceous unit. J Clin Pathol 2007;60:129-44.
Fletcher CDM, ed. Diagnostic Histopathology of Tumors. 3rd Ed. Philadelphia, PA: Elsevier; 2007: 1442.
Howard MS, Smoller BR. Trichofolliculoma: eMedicine. Last updated on March 26, 2009. Available at: emedicine.medscape.com/article/1060303-overview
Rapini RP. Practical Dermatopathology. Philadelphia, PA: Elsevier; 2005: 285-6.