The MRI geyser sign: acromioclavicular joint cysts in the setting of a chronic rotator cuff tear.

We present the case of a 71-year-old man with a large acromioclavicular (AC) joint cyst successfully managed with surgical excision. AC joint cysts are soft tissue masses generally signifying underlying rotator cuff pathology. Traditionally, these cysts were identified with shoulder arthrography as a "geyser" of fluid escaping through the AC joint. Magnetic resonance imaging (MRI) is today's preferred imaging modality; we describe the MRI equivalent of the "geyser sign," signifying synovial fluid escaping through the cuff defect, across the subacromial bursa, and decompressing superiorly through a degenerated AC joint. Surgical management is preferred for symptomatic cysts. Based on a review of limited retrospective case series, recommendations for management of these lesions are as follows. Repair of the rotator cuff is preferable whenever possible. In the case of an irreparable defect, good results can be achieved through excisional AC joint arthroplasty and resection of the cyst base. Aspiration of these cysts should not be attempted, due to the high recurrence rate and potential for a draining sinus. Hemiarthroplasty also may be effective in indirectly decompressing these cysts; but given the invasive nature of this procedure, it should be reserved for patients who are also symptomatic from cuff arthropathy.