Assessment of interclass and intraclass variability of specific lesions of sacroiliac magnetic resonance imaging

Aim Sacroiliac joint (SJ) imaging is the key point in the diagnosis of ankylosing spondylitis (AS). The curved anatomy of the SJ makes the interpretation of imaging difficult. The aim of this study is to evaluate the interclass and intraclass reliability of specific lesions (bone marrow edema [BME], joint space narrowing, erosions, effusion, ankylosis, bridging, sclerosis, fat deposition, and other additional pathologies) on SJ magnetic resonance imaging (MRI). Method In a total of 310 randomly chosen patients, 620 SJs were evaluated by three different radiologists with different radiology experiences of specialties other than musculoskeletal radiology. Results The agreement between readers for BME was fair to substantial, for active sacroiliitis was moderate to substantial, for sacroiliac narrowing was fair at best, for erosions was fair to moderate, for SJ sclerosis was none to slight, for chronic sacroiliitis was slight to fair, for degenerative sacroiliitis was none to slight, for normal SJ was slight, for SJ effusion was none to slight, and for fatty deposition was none. Intraclass correlation for readers 1 and 3 was usually good to excellent and for reader 2 was poor to fair. Conclusion This study was designed to assess the agreement between radiologists who were not familiar with SJ MRI. The agreement between readers was usually fair to substantial and even intraclass correlation was poor to fair for reader 2. Future studies can be designed for standardization and validation of each MRI lesion for better interpretation of SJ MRI.