MR imaging of the tarsal sinus and canal: normal anatomy, pathologic findings, and features of the sinus tarsi syndrome.

After definition of the normal anatomic features of the tarsal sinus and canal at magnetic resonance (MR) imaging, 123 ankle MR imaging studies in 116 patients were reviewed. Abnormalities of the tarsal sinus and canal were seen on MR images in 33 cases (26.8%), were highly associated with tears of the lateral collateral ligament, and could be categorized according to the pathologic findings in patients with sinus tarsi syndrome: (a) diffuse infiltration with low T1- and T2-weighted signal intensity (n = 17) consistent with fibrosis, (b) diffuse infiltration with low T1-weighted signal intensity and increased T2-weighted signal intensity (n = 11) consistent with chronic synovitis and nonspecific inflammatory changes, and (c) multiple abnormal fluid collections (n = 5) consistent with synovial cysts. Absence of the anterior microrecesses of the posterior subtalar joint was a common finding on normal MR imaging studies (46 of 90) and may reflect lack of iatrogenic joint distention. Tears of the posterior tibial tendon may have a previously unrecognized association with the sinus tarsi syndrome.