Trichofolliculoma
Trichofolliculoma is a rare, benign skin lesion that was first described in 1944. While the etiology is largely known, it is considered to be a hamartoma with follicular differentiation that results when the pluripotent skin cells cease to differentiate into the hair follicle. The lesion lacks specific predilection for gender or race but most commonly occurs on the face of adults. Clinically, trichofolliculoma presents as a solitary, skin-colored papule or nodule. It may contain a central sebum-producing pore or have a tuft of white hair protruding from the central pore, although neither of these manifestations are mandatory. Trichofolliculomas generally are asymptomatic and are not associated with any systemic or other cutaneous diseases. Therefore, no treatment is required. However, surgical excision or curettage and electrodesiccation may be performed for cosmetic reasons.
Definitive diagnosis of trichofolliculoma requires a biopsy. The histopathology shows a primary cystic structure within the dermis that may or may not be connected to the epidermis. There are multiple abnormal secondary follicles that radiate from the primary cystic structure, and the entire apparatus is surrounded by a well-circumscribed dense connective tissue. Immunohistochemical studies have revealed that trichofolliculoma is characterized by activated, aberrant cytokeratin-15 (CK15)–positive follicle stem cells that show outer root sheath differentiation while attempting to make hair. This results in disorder of the normal hair cycle.
The clinical differential diagnosis for trichofolliculoma includes dermal nevus, basal cell carcinoma, and pilar sheath acanthoma. These cutaneous entities may be ruled out by histopathology.
The histopathology of basal cell carcinoma consists of tumors of basaloid cells with little cytoplasm and hyperchromatic nuclei. There is palisading around the periphery of the tumor with stromal retraction that leads to a clefting appearance, as well as mucinous change in the stroma.
The histopathology of dermal nevus reveals small nests of melanocytes within the upper dermis that commonly localize around the pilosebaceous units. There is variability in pigmentation and cellularity of the melanocytes, and there is no junctional component.
The histopathology of pilar sheath acanthoma shows dermal proliferation of lobules comprising benign squamous epithelium that arrange themselves around small cystic spaces. The lobules themselves are surrounded by eosinophilic basement membrane.
The case and photo were submitted by Victoria Billero, MS; Adam Wulkan, MD; and Caroline Winslow, MD, all of the department of dermatology, University of Miami (Fla.).
Dr. Bilu Martin is a board-certified dermatologist in private practice at Premier Dermatology, MD, in Aventura, Fla. More diagnostic cases are available at edermatologynews.com. To submit a case for possible publication, send an email to dermnews@frontlinemedcom.com.