Folliculoma Workup

Updated: Jun 19, 2018
  • Author: Kristen D Fajgenbaum; Chief Editor: Dirk M Elston, MD  more...
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Approach Considerations

Trichofolliculomas may be easily diagnosed when they have the classic presentation of a single papule on the face with a central punctum and hair. When presentation is atypical, a biopsy may be necessary to distinguish a folliculoma from more serious lesions.


Laboratory Studies

Once the diagnosis of folliculoma is established, either clinically or histologically, no laboratory workup is indicated.


Imaging Studies

No imaging studies are indicated for this entity.


Histologic Findings

Folliculomas demonstrate a central pore leading to a large cavity in the dermis. The cavity reveals buds of hair roots on the sides and a 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.

Classic microscopic findings of a trichofolliculom Classic microscopic findings of a trichofolliculoma with smaller radially budding hair follicles opening to a large central follicle. A dense eosinophilic stroma surrounds the tumor (hematoxylin and eosin, 40x).
Folliculosebaceous cystic hamartoma (sebaceous tri Folliculosebaceous cystic hamartoma (sebaceous trichofolliculoma) is a variant of trichofolliculoma with extensive sebaceous differentiation in the follicular buds emerging from the larger central follicle (hematoxylin and eosin, 40x).

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. [15] 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.

Trichohyalin is expressed in the secondary hair structures of folliculomas, as demonstrated by their interaction with antitrichohyalin antibody AE 15. [16] The antitrichohyalin antibody AE 15 identifies cell lineage that differentiates into inner root sheath.

Merkel cells in various stages in folliculomas have a distribution similar to the known arrangement of Merkel cells during the normal follicular cycle. [17] This further demonstrates that trichofolliculomas are hamartomas with follicular differentiation. However, the failure of antibodies against neurofilaments to detect innervated Merkel cells in folliculomas distinguishes them from normal follicular cells. [17]

The stroma of folliculomas consists of spindle cells and usually has peripheral inflammation containing lymphocytes, histiocytes, plasma cells, and granulomas. [7] Androgen receptors can be found in the spindle cells of the stroma. [7]

Immunohistochemical studies with cytokeratins reveal that folliculomas differentiate mainly toward the hair bulge and the outer root sheath in the isthmus. [18] CK-17 expression in the inner and outer root sheaths is much stronger than in normal hair follicles. PHLDA1 and BerEP4, which are expressed in normal hair follicles, may also be observed in folliculomas. [7]