Trichofolliculoma ICD-10 D23.9
Trichofolliculoma is a benign tumor of the skin arising from hair follicle tissue. It is most commonly found on the face and nose. It appears as a flesh-colored nodule, which occasionally is whiteish. Histologically, it is often described as a hamartoma with differentiation towards the hair follicle.
Trichofolliculoma has been reported in all age groups, but most reports involve adults. Some studies have found a slight male predominance, however, the exact incidence is unknown.
Etiology and Pathophysiology
The etiology of trichofolliculoma is unclear. A link with inhibition of BMP signaling in P-Cadherin positive skin stem cells has been suggested in animal models. Artificially blocking BMP signaling in skin stem cells was found to produce trichofolliculoma-like growths in mice models.
Trichofolliculoma is characterized by a primary follicle in a large cystic space lined by squamous epithelium. It is surrounded by branches of secondary and tertiary follicle sprouts. The sprouts are often only partially developed and growth appears to have terminated prematurely. The growths appear in multiple phases of the normal development of a hair follicle (anagen, catagen, telogen). There is keratinized stratified epithelium present with keratohyaline granules. Cytokeratin has been used to study the origin of trichofolliculoma and has shown that it is differentiated towards development into the outer root sheath and hair bulge. It has been suggested that trichofolliculoma further develop into other lesions, such as folliculosebaceous cystic hamartoma, but this is disputed. There is evidence that older trichofolliculoma begin to display sebaceous elements, however, this could be due to differential expression and not an evolution of the primary lesion.
Trichofolliculoma is mostly found on the face with the most common locations being the nose, cheek, and ear. A variety of other locations have also been reported. Trichofolliculoma is isolated and has not been shown to be associated with any systemic conditions.
There are reports of trichofolliculoma appearing on the upper and lower eyelids, but it is exceedingly rare with only a handful of case reports mentioning this presentation.  There is one reported case of recurrent trichofolliculoma following excision.
The lesions are most often asymptomatic and frequently are without significant growth. The nodule is most often fleshy with an umbilicated central depression. Characteristic white hair may be present. Patients may complain of a nodule or growth on the eyelid, discomfort with blink, whitish discharge, or abnormal hair growth. Patients report frequently traumatizing the area and may pull or pluck the hair. 
The diagnosis is confirmed by histopathologic analysis after biopsy.
The differential diagnosis for trichofolliculoma is broad and should include both benign and malignant conditions:
- Molluscum contagiosum
- Basal cell carcinoma
- Dermal Nevus
- Epidermal inclusion cyst
- Sebaceous hyperplasia
Management is simple and involves excision of the lesion. Care should be taken during histological analysis to exclude malignant conditions. Recurrence has been reported in only one case. The lesion should be examined to ensure complete removal.
Prognosis and Complications
The prognosis for trichofolliculoma is very good. There are no systemic manifestations and the tumor is benign without a single report of metastasis and only one of invasion. Possible complications could include bleeding and infection. If the tumor occurs on the medial canthus, damage to the canalicular system is a possibility during removal. Follow up should include close examination of the excision site for signs of infection.
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