MR imaging of the normal and abnormal retrocalcaneal bursae

OBJECTIVE. The aim of this study was to define the MR imaging criteria for normal and abnormal retrocalcaneal bursae. SUBJECTS AND METHODS. Fifty ankles in 25 asymptomatic volunteers and 30 ankles in patients with Achilles tendon disorders underwent MR imaging. Increased signal intensity consistent with fluid or synovium outlining the retrocalcaneal bursa was measured. RESULTS. Of 80 bursae, 77 (96%) had measurable fluid or synovial signal intensity revealed by MR imaging. Asymptomatic volunteers had average bursal dimensions of 1 mm in the anteroposterior dimension, 6 mm in the transverse dimension, and 3 mm in the craniocaudal dimension. Bursal dimensions greater than 1 mm, 11 mm, or 7 mm, respectively, were not seen in asymptomatic subjects but were seen in 16 (53%) of 30 ankles of patients with Achilles tendon disorders. CONCLUSION. On MR imaging, the asymptomatic retrocalcaneal bursa normally contains detectable high-signal-intensity fluid or synovium or both. A bursa larger than 1 mm anteroposteriorly, 11 mm transversely, or 7 mm craniocaudally is abnormal.