An 85-year-old woman with no significant past medical history presented with a rapidly growing mass on her left shoulder (Figure 1), with no history of trauma. On physical examination, the mass was hard and non-mobile.
A shoulder X-ray and ultrasound scan were performed in order to rule out malignancy.
The X-ray (Figure 2) shows a rounded, homogeneous soft-tissue density mass on the left shoulder, located just above the acromioclavicular joint (ACJ). Additionally, the humeral head is seen cranially displaced, with subsequent narrowing of the subacromial space. Osseous degenerative change can be seen in both the humeral head and the ACJ.
On the US exam (Figures 3a, 3b, and 3c), the images show a supraclavicular fluid collection, predominantly anechogenic but heterogeneous, that appears to be erupting superiorly from the acromioclavicular (AC) interval. No Doppler signal is detected. On interrogation of the rotator cuff, the exam shows the absence of the supraspinatus and infraspinatus tendons over the humeral head, as well as bony contour irregularity.
With the presumptive diagnosis of an acromioclavicular cyst secondary to a chronic massive rotator cuff tear, a percutaneous drainage was performed for symptom relief. After cytological analysis, no malignancy was detected, with cellularity (macrophages and lymphocytes on a proteinaceous background) consistent with the diagnosis of a cyst.
Acromioclavicular joint (ACJ) cysts are fluid-filled sacs that form adjacent to the ACJ, often due to underlying degenerative joint disease or rotator cuff tears. These cysts typically result from the extrusion of synovial fluid through a disrupted ACJ joint capsule, leading to pseudocyst formation [1].
Patients typically present with a visible or palpable swelling over the AC joint, along with discomfort or localised pain. The main clinical problem arises from differentiating these cysts from other soft tissue masses [1]. Imaging is crucial to confirm the presence of a cyst and to assess any underlying joint pathology. It is important to convey whether there is evidence of severe AC joint degeneration, rotator cuff damage, or communication between the joint and the cyst.
Ultrasound is typically the first-line imaging modality, allowing visualisation of the cyst and surrounding structures. Key findings include a well-defined, anechoic or hypoechoic mass near the AC joint, although this may not always be the case, as some cysts may show a heterogeneous appearance due to bleeding, infection, or proteinaceous content, as was our case. Ultrasound may also show communication between the joint and the cyst, which confirms its synovial origin (a feature known as “geyser sign” [2] (Figure 3). The absence of internal Doppler signals (Figure 3a) can also be key in ruling out an underlying solid mass. Besides, a fast growing pace (as in the case presented), makes malignancy more unlikely.
MRI is also valuable, particularly when assessing for concurrent rotator cuff tears or AC joint degeneration. X-ray can also be helpful to define the relation of the mass to bony structures and can provide indirect rotator cuff information, with humeral head cranial displacement and subacromial space narrowing often seen in massive cuff tears [3] (Figure 1). Biopsy is rarely necessary for diagnosis.
The treatment of AC joint cysts is typically conservative, focusing on alleviating symptoms by draining the cyst. Recurrence is common unless underlying joint pathology is addressed. In cases where the cyst is large, surgical options may be considered, which often involve resecting the cyst and repairing the joint. The prognosis depends on the severity of the underlying joint condition.
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Acromioclavicular cyst secondary to massive rotator cuff tear
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Based on the provided imaging (including shoulder X-rays and ultrasound images) and clinical information, a clearly prominent soft tissue mass is observed near the left acromion. The X-ray indicates significant degeneration of the acromioclavicular (AC) joint, with a noticeable protrusion seen above the AC joint. According to the ultrasound findings, the mass contains fluid or protein-rich material, appearing as hypo- or slightly mixed echogenic content, possibly communicating with the joint cavity (“geyser sign”). No apparent solid blood flow signals are observed around the mass, and there are no signs of bone destruction. The patient reports that the mass has grown quickly but without a history of trauma, and cytological analysis of the aspirated fluid showed no evidence of malignancy.
Considering the patient’s advanced age, shoulder joint degeneration, aspirate findings, and imaging results, the most likely diagnosis is an acromioclavicular joint cyst (associated with rotator cuff damage or AC joint degeneration). No cytological evidence supports a malignant tumor.
1. Conservative Management:
• Aspiration and Decompression: If the cyst is large and symptomatic, periodic aspiration can be performed to relieve symptoms.
• NSAIDs: Nonsteroidal anti-inflammatory drugs may be used to reduce local pain and inflammation.
• Periarticular Injection: For recurrent fluid accumulation or severe pain, a corticosteroid injection around the joint under medical guidance may help alleviate inflammation.
2. Surgical Treatment:
• If the cyst recurs repeatedly or is associated with a large rotator cuff tear, surgical repair of the cuff and excision of the cyst can be considered to improve AC joint pathology.
• The decision for surgery depends on the patient’s overall health, bone quality, and functional demands.
3. Rehabilitation and Exercise Prescription:
• Early Stage (Low-Intensity, Protective Training):
1) Gentle Range of Motion Exercises: Such as supported passive/active extension, abduction, internal, and external rotation of the shoulder, 1–2 times daily, 5–10 minutes each time.
2) Low-Load Isometric Exercises: Within a safe range, perform isometric contractions of the deltoid, supraspinatus, and surrounding shoulder muscles once a day, avoiding significant pain.
• Intermediate Stage (Moderate Intensity, Functional Improvement):
1) Gradually Increase Active Resistance Training: Use resistance bands or light dumbbells to strengthen shoulder muscles 2–3 times per week, 10–15 minutes each session.
2) Perform movements slowly and in a controlled manner, avoiding aggravation of the cyst or excessive pain.
• Late Stage (Enhancement and Recurrence Prevention):
1) Depending on progress, add shoulder stability exercises and overall coordination (such as light upper-limb functional training, modified push-ups, etc.).
2) Maintain 3–5 sessions of strength and flexibility training per week, gradually increasing resistance and duration.
FITT-VP Principle:
Throughout the process, closely monitor changes in shoulder pain and range of motion. If significant discomfort occurs, seek medical evaluation and adjust the plan under the guidance of a professional rehabilitation therapist or physician.
This report is for reference only and does not replace an in-person consultation or professional medical advice. Specific diagnosis and treatment should be determined by a qualified medical team, based on the patient’s actual condition.
Acromioclavicular cyst secondary to massive rotator cuff tear
