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]
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]
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.
View Image | Classic microscopic findings of a trichofolliculoma with smaller radially budding hair follicles opening to a large central follicle. A dense eosinop.... |
View Image | Folliculosebaceous cystic hamartoma (sebaceous trichofolliculoma) is a variant of trichofolliculoma with extensive sebaceous differentiation in the fo.... |
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]
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.
Author
Kristen D Fajgenbaum, University of North Carolina at Chapel Hill School of Medicine
Disclosure: Nothing to disclose.
Coauthor(s)
Christopher Sayed, MD, Clinical Assistant Professor of Dermatology, Clinician Educator, Director of Medical Student Education, Director of Hidradenitis Suppurativa Clinic, University of North Carolina at Chapel Hill School of Medicine
Disclosure: Serve(d) as a speaker or a member of a speakers bureau for: Abbvie, Inc.
Craig N Burkhart, MD, MSBS, Assistant Professor, Department of Dermatology, University of North Carolina at Chapel Hill School of Medicine
Disclosure: Nothing to disclose.
Specialty Editors
Michael J Wells, MD, FAAD, Dermatologic/Mohs Surgeon, The Surgery Center at Plano Dermatology
Disclosure: Nothing to disclose.
Jeffrey P Callen, MD, Professor of Medicine (Dermatology), Chief, Division of Dermatology, University of Louisville School of Medicine
Disclosure: Received honoraria from UpToDate for author/editor; Received royalty from Elsevier for book author/editor; Received dividends from trust accounts, but I do not control these accounts, and have directed our managers to divest pharmaceutical stocks as is fiscally prudent from Stock holdings in various trust accounts include some pharmaceutical companies and device makers for i inherited these trust accounts; for: Allergen; Celgene; Pfizer; 3M; Johnson and Johnson; Merck; Abbott Laboratories; AbbVie; Procter and Gamble; Amgen.
Chief Editor
Dirk M Elston, MD, Professor and Chairman, Department of Dermatology and Dermatologic Surgery, Medical University of South Carolina College of Medicine
Disclosure: Nothing to disclose.
Additional Contributors
Craig G Burkhart, MD, MPH, Clinical Professor, Department of Medicine, Medical College of Ohio; Clinical Assistant Professor, Department of Medicine, Ohio University College of Osteopathic Medicine
Disclosure: Nothing to disclose.
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