Folliculoma 

Updated: Jun 19, 2018
Author: Kristen D Fajgenbaum; Chief Editor: Dirk M Elston, MD 

Overview

Background

Folliculoma, also known as trichofolliculoma, is a type of benign cutaneous adnexal tumor.[1] Cutaneous adnexal tumors are neoplasms that are classified based on their morphologic differentiation towards at least one type of normal skin structure: hair follicles, apocrine glands, eccrine glands, or sebaceous glands.[2, 3]

A folliculoma is a rare, asymptomatic tumor of the hair follicle. This is a hamartoma of the hair follicle, a malformation of cells and tissues that resembles a normal hair follicle. Clinically, it appears as a small, solitary, skin-colored papule or nodule on the face or scalp. A tuft of vellus hair often protrudes from a central punctum. Folliculomas usually present in middle-aged adults, but they have been found at birth and can develop throughout life.

Pathophysiology

Trichofolliculomas represent a hamartomatous, adnexal tumor originating from the hair follicle.[4] The tumor is a benign malformation of hair follicle cells and structures. All stages of follicular development can be observed in the lesion.

A variant of the trichofolliculoma is the sebaceous trichofolliculoma. Schulz and Hartschuh suggest folliculosebaceous cystic hamartoma is a folliculoma at its very late stage.[5] Cole et al suggest no pathogenetic relationship exists with giant, congenital folliculosebaceous cystic hamartomas.[6]

Etiology

Folliculomas are caused by a maldevelopment of the hair follicle unit. Folliculomas undergo anatomical changes corresponding to the regressing normal hair follicle in its various cycles.

Epidemiology

Frequency

United States

Folliculomas are uncommon. Given their benign nature, no large screening has been performed in the general population. As a result, an exact incidence has not been determined.

International

The condition has been reported worldwide. It is a rare entity among all nationalities.

Race

A study performed with military personnel demonstrated that folliculomas are more common in whites than in any other race.

Sex

Folliculomas occur predominantly in males.

Age

The mean age of manifestation is 45 years, but lesions can be congenital or occur much later in life.[7]

Prognosis

The prognosis is excellent. Folliculomas are benign, asymptomatic lesions with no malignant potential. 

Patient Education

Patients should be informed of the benign nature of these lesions and that they require no follow-up care.

Clinically, trichofolliculomas may be confused with a more serious entity, such as basal cell carcinoma. Thus, the lesion may need to be excised to confirm the diagnosis. If excision is performed for diagnostic or cosmetic purposes, recurrence can occur if the lesion is not completely removed.[8]

 

Presentation

History

Patients present with a papule on the face, usually localized to the nose.[7] They are also found on the malar/cheek area, ears, scalp, or neck. Although one report describes multiple lesions, folliculomas usually present as solitary nodules. Lesions are asymptomatic and slow growing, with a diameter usually of 0.2-1 cm. Lesions have a central punctum, in which patients may note the presence of a vellus hair protruding.

Physical Examination

A folliculoma is a solitary tumor, most commonly found on the face or occasionally the scalp, ears, or neck. One reported case describes a congenital folliculoma on the cheek.[9] Folliculomas have also been identified in the vulva[10] and on the abdomen.[11]

The lesion is a firm, slightly elevated, pearly tumor with a central punctum. The central punctum contains keratinous material or a wisp of white, wool-like or cottony hairs protruding from it. If hairs protrude from the punctum, the diagnosis of folliculoma is strongly suggested.

On dermatoscopic examination, a distinct "firework" pattern has been described. A central hair shaft and several smaller radial dark-brown projections are scattered peripherally that correlate to nests of cells of pigmented follicular epithelium.[12] Description of a second case was less specific, with a bluish nodule, shiny-white structures, dotted vessels, and some central scale.[13]

Complications

Folliculomas are completely benign growths. No cancerous tendencies have been reported and they are not usually associated with complications. Rarely this condition has been associated with focal acantholytic dyskeratosis.[14]

 

DDx

Diagnostic Considerations

Clinically, a hair protruding from the central punctum is highly diagnostic of a folliculoma. Folliculomas are benign and require no specific therapy.

Many atypical presentations have been observed, where lesions have no central hair and occur anywhere on the body. In these cases, it may be difficult to diagnose a folliculoma clinically.

To ensure that the lesion is not a more serious entity, such as a basal cell carcinoma, a biopsy or removal is appropriate. 

Differential Diagnoses

 

Workup

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]

 

Treatment

Medical Care

Since folliculomas are benign, they require no specific therapy. Excision of the entire growth for diagnostic or cosmetic purposes is available.

Folliculomas have also been successfully treated with carbon dioxide and Er:YAG lasers.[19]

Surgical Care

Folliculomas are benign and require no specific therapy. To ensure that the lesion is not a more serious entity, such as a basal cell carcinoma, a biopsy or removal is appropriate. Patients may also opt for excision because of cosmetic reasons. Complete local excision is an adequate treatment for this entity. If folliculomas are not completely removed, regrowth can occur.[8]

Long-Term Monitoring

Folliculomas are benign, asymptomatic lesions with no malignant potential. Once diagnosed, they require no long-term monitoring.