Diagnostic Value of Diffusion Weighted Imaging in Sacroiliitis

Objective: Early diagnosis of acute sacroiliitis and related disorders are quite important for preventing the irreversible results of these diseases (such as ankylosis) and increasing the efficiency of treatment. Magnetic resonance imaging (MRI) is the most important modality in early diagnosis. Routine MRI examinations should include short tau inversion recovery and contrast enhanced fat saturated T1-weighted sequences. In our study, we evaluated the role of diffusion weighted imaging (DWI) MRI sequence in the diagnosis of acute sacroiliitis. Inter-observer and intra-observer reliability was also evaluated. Materials and Methods: Seventy patients suffering from back pain and underwent sacroiliac joint MRI between October 2008 and December 2009 were retrospectively evaluated. Patients who were under age of 18 and had MRI examinations without contrast were excluded. Routine MRI sequences and DWI sequences (b100, b600, b1000) of 84 sacroiliac joints of 42 patients were evaluated retrospectively. Evaluations were made independently without any information about patient's name and clinical findings. First, DWI MRI examinations were evaluated by two radiologists separately (one of the radiologist made another evaluation after one week). After one month, sacroiliac joint MRI's of the patients were evaluated for osteitis and bone marrow enhancement (positive MRI) by two radiologists and decisions were made by consensus. A contrast-enhanced MRI study was accepted as the gold standard for the diagnosis of active sacroiliitis in the statistical evaluation. The sensitivity and specificity of DWI for active sacroiliitis were calculated. Also intra-observer and inter-observer concordances were made by Cohen kappa test in SPSS (Statistical Package for the Social Sciences) version 16 software. Results: For the diagnosis of acute sacroiliitis, sensitivity and specificity values of DWI MRI were calculated as 82.1% and 87.5% respectively in 84 sacroiliac joints. By using Cohen's kappa test, moderate intra-observer correlation for first radiologist [kappa=0.684 (p<0.05)], weak intra-observer correlation for second radiologist [kappa=0.369 (p<0.05)] and moderate inter-observer correlation [kappa=0.512 (p<0.01)] was found. Conclusion: In conclusion, DWI MRI examination is a non-invasive (contrast material administration is not needed), sensitive, fast diagnostic method in the diagnosis of acute sacroiliitis. Besides, DWI MRI may have a potential as a screening method in suspected cases, if supported with large studies.