Proliferating trichilemmal tumor (PTT) is a rare adnexal neoplasm that arises from the outer sheath of the hair follicle. It is believed that PTTs originate in trichilemmal cysts. These tumors have the potential for malignant transformation; when this occurs, the tumor is known as a malignant PTT (MPTT). Recurrence after simple local excision is common, and it can cause considerable morbidity. We report a case of MPTT that was initially diagnosed as a benign PTT. The primary tumor had arisen from the skin over the glabella. It was excised, but it recurred 3 years postoperatively. The recurrent tumor involved the eyelid, nasal cavity, and frontal and ethmoid sinuses, and it extended into the orbit. The recurrent tumor was excised via combined endoscopic and open surgery. As far as we know, this is the first documented case of an MPTT that involved the sinuses.
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