The geyser sign is the flow of arthrographic contrast or joint fluid from the glenohumeral joint across the acromioclavicular joint (ACJ) to form a supraclavicular collection. It is seen in some cases of long-standing rotator cuff tear and advanced degenerative change of the shoulder.
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Clinical presentation
It may present as a pseudotumor above the acromioclavicular joint which is classically described as slow-growing.
Pathology
Chronic rotator cuff degenerative change and full-thickness tearing lead to instability of the humerus in the glenohumeral joint. Eventually, chronic impaction from the humeral head disrupts the inferior acromioclavicular joint capsule, and glenohumeral joint fluid "erupts" superiorly through the acromioclavicular interval from the subacromial-subdeltoid bursa and glenohumeral joint.
Radiographic features
Plain radiography
There is often a high riding humeral head abutting the acromion or acromioclavicular joint indicating rotator cuff tears. There may be signs also of rotator cuff arthropathy.
Conventional arthrography
after injection of arthrogram solution into the glenohumeral joint, the solution will decompress and extend into the subacromial-subdeltoid bursa (through the cuff tear) and into the acromioclavicular joint
Ultrasound
background advanced degenerative changes in the shoulder with a full-thickness rotator cuff tear, as with a bare humeral head sign
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hypoechoic fluid collection above the acromioclavicular joint
ensure that the collection is genuinely fluid and not an exuberant hypoechoic degenerative change of the acromioclavicular joint or mass with color Doppler
MRI
background advanced degenerative change in the shoulder with a full-thickness rotator cuff tear
T2: hyperintense fluid tracks from the glenohumeral joint space into the subdeltoid bursa and into acromioclavicular joint
Differential diagnosis
cystic neoplasm
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