Purpose: To analyze the type and frequency of abnormalities of the sacroiliac joint (SIJ) in early seronegative spondylarthropathy (SpA) by MR in comparison with CT and radiography, assess the most appropriate MR sequences to be used, and introduce a new way of grading MR abnormalities of the SIJ.
Material and methods: The SIJs of 41 patients with early SpA (median duration of inflammatory low back pain of 19 months) were evaluated by MR imaging using STIR, T1, T2, and T1 fat saturated (FS) sequences before and after i.v. Gd contrast medium followed by staging of abnormalities. The findings were compared with those obtained by CT and radiography.
Results: MR and CT had equal efficacy superior to radiography in staging of erosions and osseous sclerosis. Only MR allowed visualization and grading of active inflammatory changes in the subchondral bone and surrounding ligaments in addition to bone marrow fatty accumulations. T2-weighted sequences did not contribute to assessment of sacroiliitis.
Conclusion: MR of the SIJs is reliable in its visualization of joint erosions in early SpA and allows differentiation between active and chronic sacroiliitis. We recommend the following sequences: semicoronal T1 and both semicoronal and semiaxial STIR. If these images are normal, the examination can be finished; otherwise additional semicoronal T1 FS before and after i.v. contrast has to be performed as well as semiaxial post-contrast T1 FS.