Isolated synovial cyst of the acromio-clavicular joint associated with joint degeneration and an intact rotator cuff.

The majority of acromioclavicular joint cysts are the manifestation of underlying pathology of the rotator cuff. A chronic rotator cuff tear should be the first option in differential diagnosis, when facing such a condition, although this is not always the case. A case of a 67-year-old male patient, who abruptly developed a painless lump over his right acromioclavicular joint, is presented. Imaging studies were diagnostic for a cystic lesion, and degeneration of the acromioclavicular joint without communication with the subdeltoid bursa and the glenohumeral joint. The rotator cuff was intact. Surgical treatment, with cyst removal and resection of the distal end of the clavicle, was performed. The lesion was proved to be a synovial cyst. Eighteen months postoperatively, the patient was asymptomatic and no recurrence of the cyst was evident.