Juxta-articular myxoma of the shoulder presenting as a cyst of the acromioclavicular joint: A case report

Abstract

Treatment of patients with subcutaneous cystic lesions of the acromioclavicular joint has yielded unpredictable results unless the underlying pathologic process producing the cyst is addressed.4,9 Three causes of this lesion have been reported in the literature: true ganglion,9,2 mechanical irritation of a degenerated acromioclavicular joint by direct contact with the humeral head through a rotator cuff defect,8 and up-welling of glenohumeral joint fluid through a rotator cuff defect (“geyser” sign).3,4 We report a case of juxta-articular myxoma of the shoulder involving both the acromioclavicular joint and the glenohumeral joint in the presence of a large rotator cuff tear as an additional cause of acromioclavicular cyst. The aggressive behavior of this lesion compared with other known causes warrants the attention of surgeons who evaluate and treat this condition. CASE REPORT A 68-year-old right-hand-dominant man had a soft tissue mass over the superior surface of his right acromioclavicular joint compatible with subcutaneous acromioclavicular cyst. The lesion was excised by a general surgeon in the patient’s home district but recurred 5 weeks later. The cyst was reexcised, and a pathologic diagnosis of juxta-articular myxoma was confirmed by the Armed Forces Institute of Pathology. Two months later recurrence in the same location prompted referral to our facility for evaluation and further treatment. Physical examination showed a 2.5-cm marble-sized soft tissue mass superior to the right acromioclavicular joint with marked erythema, shiny skin edges at the previous scar, and dense induration and firm attachment to the underlying acromion. Glenohumeral range of motion was unrestricted; no pain was elicited on motion examination. After routine radiography was performed, computed tomography scan indicated erosion of the acromioclavicular joint and apparent cystic change in the humeral head. Magnetic resonance imaging evaluation of the shoulder with the 1.5-Tesla Siemens Magnetom System suggested a chronic rotator cuff tear, subdeltoid fluid, a synovial or gan