What causes the pseudotumor above the acriomioclavicular joint?
A geyser ganglion, due to a a long-standing rotator cuff tear and advanced degenerative change of the shoulder.
Chronic full thickness defect of the supraspinatus and infraspinatus tendon with rotator cuff arthropathy.
Degeneration of the acromioclavicular joint with large amount of glenohumeral joint fluid "erupting" superiorly through the acromioclavicular interval into the subdeltoid bursa.