MRI findings in patients with tibial nerve compression near the knee

The soleus sling has been recently identified as a site of compression of the tibial nerve resulting in tibial neuropathy. Diagnosis of soleal sling syndrome is difficult, and has been based mainly on clinical examination. Advances in MR imaging with high-resolution 3-Tesla scanners have made direct visualization of nerve pathology possible. With the use of high-resolution imaging and fat-suppression protocols, tibial nerve compression at the soleal fascial arch can be demonstrated in a subset of patients presenting with idiopathic tibial neuropathy. The purpose of this paper is to confirm the ability of MR imaging to demonstrate pathologic changes in the tibial nerve in patients presenting with soleal sling syndrome. Additionally, patients presenting with tibial neuropathy and ganglion cysts, both extra- and intraneural, were examined to determine if the site of compression corresponded to the region of the soleus sling. Nine patients were included in the study, two with idiopathic soleus sling syndrome, four with extraneural, and three with intraneural ganglion cysts. In the patients presenting with idiopathic soleus sling syndrome, MR imaging demonstrated a thickened soleus sling with T2 hyperintensity of the tibial nerve at the level of the sling and denervation changes in muscles of the posterior compartment of the leg. In patients with extraneural ganglion cysts, MR imaging demonstrated a "sandwich"-like compression of the tibial nerve between the cyst and the soleus sling with corresponding tibial nerve T2 hyperintensity and denervation change in posterior compartment muscles. No compression of the tibial nerve at the soleus sling was found in the intraneural ganglion population. We conclude that MR imaging is effective in demonstrating pathologic changes in the tibial nerve at the soleus sling. Based on the MRI findings, we also believe that the soleus sling is a component of the compression when patients present with extraneural ganglion cysts and tibial neuropathy near the knee; in these patients, we recommend release of the soleus sling as part of the definitive management.