A 7-year-old girl presented with painful swelling of the right knee and a history of juvenile idiopathic arthritis (JIA). MRI revealed a large joint effusion with thick synovial enhancement (Fig. 1) containing multiple near-uniform-size punctate hypointense lesions on T2-W images consistent with rice bodies (Fig. 2). Significant hyperemia was seen within the articular cartilage (Fig. 2).

Fig. 1
figure 1

Synovial enhancement (arrows)

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Fig. 2
figure 2

Rice bodies (arrowheads) and articular cartilage hyperemia (white arrow)

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Rice bodies were initially described in patients with tuberculous arthritis [1]. The term “rice body” comes from its macroscopic resemblance to grains of polished rice. Microscopically these contain mostly fibrin and collagen products as well as inflammatory cells and a few blood vessels [2]. Alternative diagnostic considerations include chronic nontuberculous septic arthritis, pigmented villonodular synovitis (unlikely, because of a lack of signal consistent with hemosiderin), nonpyogenic inflammatory arthritis such as JIA, as seen in our patient, and less likely, because of the child’s age, primary synovial chondromatosis [2]. In our patient, the acute manifestations of JIA were manifested by synovitis and cartilage hyperemia, and the chronic changes were manifested by the innumerable rice bodies.