Value of unenhanced spin-echo MR imaging in distinguishing between synovitis and effusion of the knee.

OBJECTIVE: We performed a study to determine if unenhanced spin-echo MR imaging can be used to differentiate effusion from synovitis of the knee joint.

MATERIALS AND METHODS: Unenhanced spin-echo MR imaging examinations of 1051 consecutive patients referred for evaluation of internal derangement of the knees were reviewed. Twelve of 550 knees with significant joint effusion also had thickened or irregular synovium. Of these, the cause of synovitis was proved in 10 patients. In the other two, the cause was unknown.

RESULTS: Thickened synovium was of intermediate signal intensity on T1-weighted MR images compared with the lower signal intensity of joint effusion. In eight cases, the thickened synovium had an intermediate signal intensity on T2-weighted images relative to the high signal of the joint effusion. MR images in the other four cases showed increased signal intensity indistinguishable from that of joint effusion.

CONCLUSION: Our experience suggests that unenhanced spin-echo MR images can be used to distinguish synovitis from effusion in the knee joint.