Cutaneous metaplastic synovial cyst of the cheek generated by repetitive minor trauma.

Cutaneous metaplastic synovial cyst (CMSC) refers to a cyst lined by metaplastic synovial tissue including villous structures. It is thought to be a tissue reaction to local trauma, and most cases have a history of preceding surgery or trauma. Clinically, most of the lesion is a tender intradermal nodule that is associated with scar tissue. However, dermatologists have difficulty in diagnosing CMSC because CMSC is reported only rarely and its clinical manifestation can be confused with implantational epidermal cyst, suture granuloma or other cutaneous cysts. Thus, a histopathological exam is mandatory for diagnosis of CMSC. Herein we report the case of an 18-year-old man who developed CMSC on the left cheek on the posterior ramus of the mandible. He had a history of repetitive digital manipulation of the lesion before the onset of CMSC.