Trichilemmoma

Trichilemmomas are benign follicular neoplasms that exhibit differentiation toward the outer root sheath of the pilosebaceous follicular epithelium. Trichilemmomas clinically present as individual or multiple, slowly growing, verrucous papules appearing most commonly on the face or neck. The lesions may coalesce to form small plaques. Although trichilemmomas typically are isolated, patients with multiple trichilemmomas require a cancer screening workup due to their association with Cowden disease, which results from a mutation in the phosphatase and tensin homolog tumor suppressor gene, PTEN. An easy way to remember the association between trichilemmomas and Cowden disease is to alter the spelling to “trichile-moo-moo,” using the “moo moo” sound of an animal cow as a clue linking the tumor to Cowden disease.

The differential diagnosis for trichilemmoma includes inverted follicular keratosis, squamous cell carcinoma in situ, verruca vulgaris, and warty dyskeratoma.