Pseudodefect of the talar dome: an anatomic pitfall of ankle MR imaging.

Abstract

To identify a normal groove in the posterior aspect of the talus as a potential pitfall in interpretation of ankle magnetic resonance (MR) images. In 40 patients, T1-weighted spin-echo and T2-weighted fast spin-echo sagittal MR images were retrospectively reviewed from 47 consecutive routine ankle examinations. The patients were referred for evaluation of ligament and tendon abnormalities, such as tendinitis and tear, and suspected osseous and osteochondral injuries. Images were assessed for the presence of an erosion-like defect in the posterior aspect of the talar dome. Radiographs were available in 13 cases. Sagittal T1-weighted spin-echo sequences were also performed in 14 embalmed cadaveric ankles, followed by sectioning and dissection of three specimens. A defect was seen in 45 of 47 ankle MR imaging examinations. Radiographs did not show the defect. All 14 cadaveric ankles demonstrated the defect at MR imaging. At anatomic dissection, the defect was a normal groove for the passage of the posterior talofibular ligament. The pseudodefect of the talar dome is a normal groove for the posterior talofibular ligament and should not be misinterpreted as an articular erosion or osteochondral defect.