Proliferating Trichilemmal Tumor of the Knee Mimicking Prepatellar Bursitis on Ultrasonogram: A Case Report

Proliferating trichilemmal tumor is a rare benign tumor of skin appendage. It is usually solitary, more common in women after the fourth decade of life, and almost exclusively confined to the scalp and back of the neck. We report herein an unusual case of proliferating trchilemmal tumor which occurred on the knee.