Metaplastic synovial cyst in male breast.

Metaplastic synovial cyst (synovial metaplasia of the skin) refers to a cyst lined by a membrane resembling hyperplastic synovial villi. Synovial-like metaplasia has been described around prostheses and breast implant capsules and may occur in postsurgical cutaneous scars, unrelated to prostheses or implants. We describe a metaplastic synovial cyst occurring in the left breast of a 23-year-old man 2 years after surgical treatment of gynecomastia. The expanding clinicopathologic scenario of metaplastic synovial cyst, in scar tissue in male breast unrelated to mammary implants, and as a potential complication after surgical treatment of gynecomastia is highlighted.