Acromioclavicular joint cysts are benign lesions, either ganglionic or synovial in etiology.
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Clinical presentation
Patients present with a soft, slightly painful mass above the acromioclavicular joint (ACJ), sometimes slightly limiting the shoulder range of motion.
Pathology
Classification
They can be divided into two types per the Hiller classification according to their etiology 3:
type 1: in advanced acromioclavicular joint arthritis without rotator cuff tear from degenerative changes in the acromioclavicular joint irritating the synovium, with overproduction of fluid and subsequent formation of superficial cysts at the joint
type 2: in chronic rotator cuff tear with superior migration of the humeral head, resulting in irritation and deterioration of the acromioclavicular joint capsule, increased synovial fluid production causes glenohumeral joint fluid to leak into the communicating acromioclavicular joint to produce cysts (Geyser sign)
Radiographic features
Plain radiograph
Swelling of the acromioclavicular joint that shows arthritic changes.
Ultrasound
Anechoic formation, sometimes sepimented, over the acromioclavicular joint, without blood flow.
MRI
High T2 signal in homogeneus multilocular mass on the acromioclavicular joint.
Treatment and prognosis
The treatment of AC joint ganglion cysts can be either conservative or surgical, with surgical options including:
type 1: surgical excision with resection of the lateral clavicle
type 2: reverse shoulder arthroplasty (RSA)
In elderly patients with no symptoms and no discomfort, a conservative treatment approach is often preferable.
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