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]
-
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 trichofolliculoma) is a variant of trichofolliculoma with extensive sebaceous differentiation in the follicular buds emerging from the larger central follicle (hematoxylin and eosin, 40x).
