Case Report

The following microscopic pictures are from an excised 0.8 cm skin-colored nodule of the upper lip of a 49-year-old man. The lesion has been present for an unknown period of time.

Figure 1

Fig 1. The raised epidermis is intact. The dermis shows a mostly solid and focally cystic dermal tumor attached to the epidermis. The periphery of the tumor is well circumscribed. Note the cystic space containing eosinophilic material on the left side, peripheral basaloid cells and central sclerotic area infiltrated by small epithelial cells

Figure 2

Fig 2. Higher magnification of the cystic area shows somewhat pale red trichilemmal-type epithelium in the cyst wall and tritilemmal-type compact keratin in the cyst cavity.

Figure 3

Fig 3. Central sclerotic area showing small epithelial cells within the dense stroma

Figure 4

Fig 4. Higher magnification of the sclerotic area showing cords and single small epithelial cells with in dense sclerotic stroma. Note the dense lymphocytic infiltrates on the right.

Diagnosis: Desmoplastic tricholemmoma.

Comment

The purpose of this brief communication is to alert pathologists to the histologic features associated with a rare variant of trichilemmoma, which may easily be mistaken for carcinoma of the skin or adnexa.

Desmoplastic trichilemmoma is a rare trichilemmoma variant arising from the outer root sheath or infundibular epithelium and occurring predominately on the face of affected individuals. The patient commonly presents with a slow-growing, solitary, dome-shaped papule. Simple excision of the lesion is the treatment of choice and is curative. There is no association of the lesion with Cowden’s disease.

Histologically, desmoplastic trichilemmoma shows a biphasic pattern of usual trichilemmal cell lobules at the periphery with a central or sometimes peripheral sclerotic/hyalinized area, containing small epithelial cells with an “infiltrative” appearance. These morphologic features may be misinterpreted as trichilemmal carcinoma, squamous cell carcinoma, sclerosing basal cell carcinoma, and/or basosquamous cell carcinoma.