A Case of a Giant Trichilemmal Cyst on the Forehead.

Trichilemmal cysts are the most common benign subcutaneous cysts on the scalp. Approximately 90% of trichilemmal cysts appear on the scalp and have trichilemmal keratinization without a granular layer visible on pathological examination. In addition, proliferating trichilemmal tumors, which occur in 2% of trichilemmal cysts, show local recurrence and ulceration, making them highly locally aggressive and requiring careful differentiation. We report the case of a 56-year-old man with a giant trichilemmal cyst on his forehead. After computed tomography and magnetic resonance imaging, a subcutaneous cyst was suspected and excised, and a pathological diagnosis of trichilemmal cyst was established. This was a rare case as the trichilemmal cyst was not located on the scalp, the most common site, but on the forehead area, and it was exceedingly large, with a maximum diameter of 9 cm.