Background: Tarsal tunnel syndrome(TTS)is an entrapment neuropathy of the posterior tibial nerve within the tarsal tunnel below the medial malleolus. An accurate diagnosis is difficult, and TTS is usually diagnosed from clinical symptoms due to the lack of accurate diagnostic tools. We aimed to standardize the diagnosis of TTS using MRI, and report the MRI conditions for clear visualization of the tarsal tunnel.
Methods: We investigated which sequences and MRI conditions would be appropriate for the imaging of the tarsal tunnel in a healthy volunteer. As in routine brain MRI, the imaging time was within 15 minutes. We also performed an MRI study of the tarsal tunnel in two patients with TTS.
Results: Axial images obtained by fat-suppression 3-dimensional T2*-weighted imaging(3D-T2*WI)are the most useful for visualization of the tarsal tunnel. The axial images obtained by T2-weighted imaging(T2WI)and T1-weighted imaging(T1WI)were also useful for visualization of the area around the flexor retinaculum. The appropriate slice thickness was determined to be 1.5 mm, based on the resolution and photographic time. The flip angle, necessary for tissue resolution, was set at 15° because it provided the clearest image and highest contrast between different tissues. The total photographic time was within 14 minutes, and it is acceptable for routine MRI studies of TTS. In the two cases of TTS included in this study, the tarsal tunnel was clearly visible.
Conclusions: For diagnosis of TTS using MRI, axial images obtained by fat-suppression 3D-T2*WI, 2-dimensional(2D)-T2WI, and 2D-T1WI are recommended. A coronal image obtained by reconstruction of fat-suppression 3D-T2*WI might be useful for anatomical understanding. In future studies, we plan to evaluate patients with TTS using the above protocol.