Acromioclavicular joint cyst

Case contributed by Dr Michael P Hartung

Presentation

Nonpainful palpable mass in the right shoulder for 2 weeks. History of rotator cuff surgery.

Patient Data

Age: 70
Gender: Female

Round fluid attenuation (10 HU) structure in the right shoulder soft tissues which appears to communicate with the acromioclavicular joint. This corresponds to the area of palpable concern (linear marker present superficially). 

Annotated images

CT

Arrows indicate the location of the cyst in all three imaging planes. 

Case Discussion

Chronic rotator cuff instability can result in tearing of the acromioclavicular joint capsule, allowing glenohumeral joint fluid to "escape" into the shoulder soft tissues, resulting in a fluid-filled mass. This should not be mistaken for malignancy. In this case, a contrast-enhanced CT was ordered by the referring clinician due to the concern of malignancy, which was likely an unnecessarily aggressive work-up, as this could have been quickly diagnosed with ultrasound at lower cost and no radiation. 

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