- Author: Craig G Burkhart, MD, MPH; Chief Editor: Dirk M Elston, MD more...
Once the diagnosis of folliculoma is established, either clinically or histologically, no laboratory workup is indicated.
No imaging studies are indicated for this entity.
Folliculomas demonstrate a central pore leading to a large cavity in the dermis. The cavity reveals buds of hair roots on the sides and base of numerous well-formed sinuses. These maldeveloped hair follicle units possess a dermal papilla, a hair matrix, and the rudiments of root sheaths. Some of these hamartomatous hair units may form fine hair shaft structures, while others only produce keratinous fragments.
Pilomotor muscles and sebaceous glands are either not present or rudimentary in appearance. Some have described the sinus tracts as secondary follicles branching from the walls of the primary or main cavity. In the outer sheaths of these secondary follicles, large amounts of glycogen can be found. Additionally, these secondary epithelial proliferations may contain small keratinous cysts and vellus hair shafts.
Using antibodies to Ki67, proliferative Merkel cells have not been detected in folliculomas. Trichohyalin has been expressed in the secondary hair structures of folliculomas by antitrichohyalin antibody AE 15.
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