Trichilemmal Cyst with Ossification and Marrow Formation: A Case Report

Trichilemmal cysts, also known as sebaceous or pilar cysts, are found as solitary or multiple intradermal or subcutaneous nodules with a predilection for the scalp. They are derived from the isthmus of the hair follicle. They have keratinous material, which may contain cholesterol clefts and calcifications, in the lumen. Ossification with marrow formation is extremely rare. Here, we report an unusual case of ossifying trichilemmal cyst in a 40-year-old healthy woman. The possible mechanism is the formation of bone from osteogenic stromal elements secondary to cyst wall rupture.