Teaching Case

A 57-year-old female patient with a history of longstanding seronegative, ANF-positive rheumatoid arthritis presents to the department of orthopedic surgery with shoulder pain.

Plain radiography of the right shoulder revealed degenerative changes at the acromioclavicular joint and sclerotic delineated erosions at the humeral head (Fig. 1). Conventional Arthrography of the right shoulder showed irregular delineation of the joint capsule with multiple intra-articular filling defects and a partial articular infraspinatus tear (Fig. 2). Subsequent MR Arthrography confirmed erosions at the anatomical neck, the partial articular tear of the infraspinatus tendon and the intra-articular foci of intermediate signal on both pulse sequences, in keeping with rice bodies (Fig. 3). Plain radiographies of the hands and feet performed at a previous date showed sequelae of longstanding rheumatoid arthritis (Fig. 4).

The term rice body was originally coined in 1895 due to its resemblance to polished grains of rice [1]. Rice bodies are considered a non-specific response to synovial inflammation, most commonly found in rheumatoid arthritis (RA) [2]. Other causes of rice body formation are tuberculous arthritis, septic arthritis and spondyloarthropathy [3, 4].
Its pathogenesis is not fully understood. Most authors believe that rice bodies result from micro-infarcts in hypertrophic synovium, leading to detachment of synovial free fragments into the joint cavity. Histologically rice bodies consist of acidophilic amorphous core surrounded by fibrin and collagen [3, 4]. They appear to be unrelated to disease activity, severity or duration [1, 2, 5, 6].
Plain radiography (CR) is usually nonspecific and adds little in the diagnosis. Although CR may show marginal erosions as a consequence of longstanding underlying joint disease in RA, direct visualisation of rice bodies, however, is impossible. Conventional arthrography may reveal multiple intra-articular filling defects. Ultrasound shows multiple hyperechoic, intra-articular loose bodies, associated with signs of arthritis including hypervascular synovial inflammation, bursitis and erosions [4]. The imaging modality of choice is MRI or MR arthrography. On MRI, rice bodies appear as multiple intra-articular foci iso- or hypointense to skeletal muscle on T1-weighted images (WI) and hypointense on T2-WI [2-5].
The differential diagnosis on imaging includes synovial chondromatosis, pigmented villonodular synovitis (PVNS) and lipoma arborescens. Synovial chondromatosis may be primary or secondary due to underlying joint disease. The signal intensity of the intra-articular loose bodies is variable according to the stage of the disease. Loose bodies may contain hyaline cartilage in the initial stage, which may later calcify or ossify. PVNS is characterised by hypointense synovial structures on both pulse sequences and shows blooming artefacts on gradient echo imaging, due to the presence of hemosiderin. In joints with a tight capsule bone erosions are often associated. Lipoma arborescens consist of a subsynovial lipomatous soft tissue proliferation which is isointense to fat on T1- and T2-WI [7].
Removal of rice bodies may correlate with clinical improvement in affected joints [1, 2]. Some authors recommend aspiration or arthroscopic lavage or surgical synovectomy as potential treatment options [1, 3, 4].
In conclusion, rice bodies are a relatively uncommon imaging finding in patients with longstanding articular disease. Meticulous analysis of the imaging findings, knowledge of underlying joint disease, such as RA, and correlation with previous imaging allows a correct diagnosis.