CASE 18838 Published on 23.01.2025

Acromioclavicular cyst secondary to massive rotator cuff tear

Section

Musculoskeletal system

Case Type

Clinical Case

Authors

Mikel Elgezabal, Constanza Elizabeth Garrido, Borja Canteli

Department of Radiology, Cruces University Hospital, Barakaldo, Spain

Patient

85 years, female

Categories
Area of Interest Musculoskeletal joint ; Imaging Technique MR, Ultrasound
Clinical History

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.

Imaging Findings

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.

Discussion

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.

Written informed patient consent for publication has been obtained.

Differential Diagnosis List
Acromioclavicular joint traumatic injury
Degenerative acromioclavicular joint changes
Acromioclavicular cyst
Soft-tissue tumour
Acromioclavicular cyst secondary to massive rotator cuff tear
Final Diagnosis
Acromioclavicular cyst secondary to massive rotator cuff tear
Case information
URL: https://www.eurorad.org/case/18838
DOI: 10.35100/eurorad/case.18838
ISSN: 1563-4086
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