MR imaging of radiation osteitis in the sacroiliac joints

The purpose of this study was to analyze magnetic resonance (MR) images of radiation osteitis of sacroiliac joints, retrospectively. Seven patients with radiation osteitis, which was diagnosed by pelvic plain radiographs and CT images, underwent MRI. T1-weighted spin echo images and T2-weighted fast spin echo images were obtained in all patients. Four patients were examined after gadolinium injection. Major signal changes of radiation osteitis were distributed on the iliac side. T1-weighted images showed diffuse low intensity both in sacral and iliac sides. T2-weighted images showed very low intensity adjacent to sacroiliac joints, but mixed intensity was illustrated apart from joints, and high intensity in the peripheral areas. Radiation osteitis showed slight to mild, but irregular enhancement in four patients after gadolinium administration. MRI can illustrate abnormal bone change distribution and is useful for diagnosing this entity by characteristic intensity patterns on T1-weighted images with and without gadolinium and T2-weighted image. However, the diagnosis of accompanied insufficiency fractures in the area of radiation osteitis is occasionally difficult with conventional MRI.