RESUMO
The geyser sign is the flow of arthrographic contrast or joint fluid from the glenohumeral joint across the acromioclavicular joint (AC) and occurs when fluid erupts from the superior aspect of the AC joint during arthrography. The cyst's pathogenesis is linked to a rotator cuff tear and an increase in the amount of fluid in the cyst. This fluid escapes through a one-way valve created by a defect in the AC joint capsule. The cysts, which are typically painless and rest over the AC joint, cause discomfort. We present a case of a 65-year-old female with a left shoulder mass. The patient presented to the outpatient department with a history of left shoulder mass for six months. She reported an increase in size with no constitutional symptoms. She was treated with surgical excision. Although rotator cuff tears and AC joint deterioration are rather common in medical practice, cystic swelling over the AC joint is a relatively uncommon symptom. Less than 50 cases have been reported to date. AC joint cyst is a mechanical consequence of a progressive and severe rotator cuff tear that can be misinterpreted as a tumor in older people. Imaging, particularly magnetic resonance imaging (MRI), should be used to rule out malignancy and make a precise diagnosis, including recognizing the "Geyser sign" if it is present.
