Efficacy of diffusion weighted imaging in sacroiliac joint MRI in children.

Objective: Because of the immature bone marrow signal in children, assessment of the sacroiliac joint is more difficult than in adults. Aim of this study is to evaluate the efficacy of diffusion-weighted imaging (DWI) in sacroiliac joint magnetic resonance imaging (MRI).

Methods: Sacroiliac joint MRI, including DWI sequences, were evaluated by two pediatric radiologists in 54 patients with sacroiliitis and 85 completely normal controls. In MRI evaluation, subchondral bone marrow edema and contrast enhancement in the sacroiliac joints were considered as active sacroiliitis. Apparent diffusion coefficient (ADC) measurements were made in six areas from each sacroiliac joint. A total of 1668 fields were evaluated retrospectively without their diagnosis being known.

Results: When the postcontrast T1W series were referenced, the sensitivity, specificity, positive predictive value, and negative predictive value of short time inversion recovery (STIR) images in the diagnosis of sacroiliitis were 88%, 92%, 83% and 94% respectively, compared to contrast-enhanced images. False positive results in STIR images were observed secondary to the flaring signal in the immature bone marrow. ADC measurements obtained from diffusion-weighted images were recorded in all patients and healthy groups. The ADC values were 1.35x10 mm/s (SD: 0.21) in the areas of sacroiliitis, 0.44x10 mm/s (SD: 0.71) in the normal bone marrow and 0.72x10 mm/s (SD: 0.76) in the immature bone marrow areas.

Conclusion: Although STIR studies are an effective sequence in the diagnosis of sacroiliitis, they cause false positive results in immature bone marrow in children in inexperienced hands. DWI is an objective method that prevents errors in the assessment of sacroiliitis by means of ADC measurements in the immature skeleton. In addition, it is a short and effective MRI series that makes important contributions to the diagnosis without the need for contrast-enhanced examinations in children.