Magnetic resonance imaging in the detection of sacroiliitis.

The value of magnetic resonance imaging (MRI) in establishing the diagnosis of sacroiliitis was studied in 20 patients with established or suspected disease on conventional radiographs and in 10 healthy subjects. Coronal T1 weighted, axial T2 weighted and proton density MRI images of the sacroiliac joints in addition to plain film radiographs were obtained. All films were graded from 0 to 4 according to the modified New York criteria and independently for changes in joint width, erosions, sclerosis and ankylosis. Using the modified New York criteria, more abnormalities were detected by MRI than by conventional radiography (p = 0.04). This was due to the detection of definite abnormalities (grades 2-4) by MRI in joints that were graded normal or suspicious (grades 0-1) on plain films (p = 0.01). MRI tended to be superior to plain films in visualizing erosions. Only MRI detected abnormalities of articular cartilage (19 patients) and in subchondral bone marrow (7 patients). The latter 2 types represented fatty infiltration and inflammatory change. Intraobserver and interobserver variation were similar for the interpretation of MRI scans and plain film radiographs. These results suggest that MRI detects changes of established sacroilitis. Due to its ability to directly image articular cartilage it may be particularly useful in patients with early disease.