Solitary Nodule With White Hairs

The Diagnosis: Trichofolliculoma

Microscopic examination revealed a dilated cystic follicle that communicated with the skin surface (Figure). The follicle was lined with squamous epithelium and surrounded by numerous secondary follicles, many of which contained a hair shaft. A diagnosis of trichofolliculoma was made.

Microscopic examination revealed a dilated cystic follicle that communicated with the skin surface (H&E, original magnification ×40).

Clinically, the differential diagnosis of a flesh-colored papule on the scalp with prominent follicle includes dilated pore of Winer, epidermoid cyst, pilar sheath acanthoma, and trichoepithelioma.^1,2 Multiple hair shafts present in a single follicle may be seen in pili multigemini, tufted folliculitis, trichostasis spinulosa, and trichofolliculoma. On histopathologic examination, a dilated central follicle surrounded with smaller secondary follicles was identified, consistent with trichofolliculoma.

Trichofolliculoma is a rare follicular hamartoma typically occurring on the face, scalp, or trunk as a solitary papule or nodule due to the proliferation of abnormal hair follicle stem cells.^3,4 It may present as a flesh-colored nodule with a central pore that may drain sebum or contain white vellus hairs. Trichofolliculoma is considered a benign entity, despite one case report of malignant transformation.⁵ Biopsy is diagnostic and no further treatment is needed. Recurrence rarely occurs at the primary site after surgical excision, which may be performed for cosmetic purposes or to alleviate functional impairment.