Extra-articular Pigmented Villonodular Synovitis of the Subacromial Space: A Case Report

Pigmented villonodular synovitis (PVNS) is a rare, benign, proliferating disease affecting the synovium of joints, bursae, and tendon sheaths. The knee is the most common site of involvement and accounts for up to 80% of cases. Involvement of the shoulder is extremely rare. Only 1 case of involvement of the subacromial space has been reported worldwide. We report a case of localized extra-articular PVNS of the subacromial space that was satisfactorily treated with marginal excision; the disease has not recurred during an 18-month follow-up period. The clinical manifestation, treatment, and prognosis of extra-articular PVNS are poorly understood, but if the lesion is left untreated, it can invade the surrounding soft tissue and joint. Therefore, we believe that early diagnosis and treatment are important for the satisfactory management of PVNS.