"Rice Body"-Like Synovial Particles on Magnetic Resonance Imaging: What Is the Spectrum of Diagnoses?

Background: "Rice body" describes the gross appearance of hyperplastic synovial villi that develop into rice-like fibrinous loose bodies. Rice bodies have historically been associated with tuberculosis and inflammatory arthritis, but no retrospective studies have correlated their magnetic resonance imaging (MRI) appearances to histology or to the underlying diagnoses. Purpose: We sought to correlate the appearance on MRI of rice body-like particles with histology and describe the associated diagnoses. Methods: We conducted a retrospective cross-sectional study of MRI reports in our institutional imaging database in which a radiologist described "rice bodies." The search was performed by a keyword search for "rice," ultimately yielding a total of 100 patients between June 1992 and July 2022. Patients were excluded if their MRI was not available for retrospective review or if there was insufficient follow-up to establish a clear underlying diagnosis. Cases were included if the MRI finding of rice bodies was confirmed by retrospective review of the images and there was clinical follow-up or surgery with histology establishing the underlying diagnosis. Results: Of the 52 patients who met inclusion criteria and were enrolled in our retrospective study, 37% (19/52) had prior surgery, 73% (14/19) being arthroplasty. Diagnoses associated with rice body-like particles on MRI were inflammatory arthritis (52%; 27/52), infection (25%; 13/52), synovial chondromatosis (8%; 4/52), osteoarthritis (6%; 3/52), bursitis (6%; 3/52), and adverse local tissue reaction (4%; 2/52). Among 13 infections, only 1 was mycobacterial while 46% (6/13) were staphylococcal and 31% (4/13) were culture-negative. In the presence of arthroplasty, rice body-like particles were associated with infection in 71% (10/14), followed by adverse local tissue reaction (14%; 2/14), 46% (24/52) underwent surgery after MRI, and 45% (10/22) had rice bodies confirmed on histology. Conclusion: Our retrospective findings suggest that rice body-like synovial particles on MRI are not specific to tuberculosis and inflammatory arthritis. Other diagnoses may also be considered, particularly nonmycobacterial infection when there is an arthroplasty. Level of Evidence: Level IV: retrospective cross-sectional study.