Bicipital Synovial Cyst in Systemic-Onset Juvenile Idiopathic Arthritis

Abstract

Figure. Contrast CT scan. Sagittal view (left) and transverse view (right) showing a large multiloculated collection of fluid along the margin of the biceps muscle extending from the synovium. A 4-year-old girl with systemic-onset juvenile idiopathic arthritis (s-JIA) relapsed while on prednisolone and ibuprofen therapy. She presented with swelling of upper left arm. The masses were firm and slightly tender, and the skin was slightly warm but not hyperemic. Ultrasonography revealed a large collection of hypoechogenic fluid (30 15 mm) along the margin of the biceps muscle. Contrast computed tomography (CT) scan showed moderate joint effusion with synovial hypertrophy. A large multiloculated collection of fluid was found along the margin of the biceps muscle extending from the synovitis (Figure). Magnetic resonance imaging (MRI) also demonstrated fluid collection with synovial hypertrophy. A large multiloculated cystic mass, hyperintense on T2-weighted MRI and hypointense on T1-weighted MRI, was seen along the margin of the biceps muscle extending from the synovitis. The collected fluid was hyperintense on fat-suppression T1-weighted MRI, suggesting that the cyst had inflammatory contents. A diagnosis of brachial synovial cyst was made. The swelling decreased and then disappeared with control of disease activity. How bicipital synovial cysts arise remains unclear. The findings in this patient demonstrate communication between the shoulder and the cyst. This might suggest that the fluid arises within the shoulder joint and then descends into the contiguous bicipital tendon sheath. The tendon eventually ruptures, leading to collection of fluid in the bicipital area. Another possibility is that the cyst arises as a collection of fluid secreted by the inflamed synovial sheath of the biceps tendon extending from the synovium of the shoulder joint. Even though bicipital synovial cyst is a rare manifestation of s-JIA, synovial cyst should be considered in the differential diagnosis in all children with s-JIA presenting with swelling of the upper arm. n