Extra-articular pigmented villonodular synovitis of the subacromial space

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 open excisional biopsy and subacromial bursectomy after diagnostic glenohumeral arthroscopy. We visualized the glenohumeral joint to rule out articular invasion and intra-articular pathology with an arthroscope, which revealed a highly vascular synovium protruding into the intra-articular area of the rotator interval, with no direct invasion by the extra-articular mass. An open excisional biopsy and subacromial bursectomy was performed. 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, early diagnosis and treatment are important for the satisfactory management of PVNS.