Imaging of foot and ankle nerve entrapment syndromes: from well-demonstrated to unfamiliar sites.

Nerve entrapment at the foot and ankle involves thin and complex anatomic structures and is underdiagnosed because clinical symptoms and electrophysiologic findings may not contribute to the diagnosis. Nerve entrapment can be secondary to acute trauma or repetitive microtrauma. The latter often results from intensive sports-related activity, inappropriate footwear, or internal foot derangement. Various lesions that occur in fibro-osseous tunnels can cause nerve compression (eg, ganglion cysts, varicosities, bone and joint abnormalities, tumors, tenosynovitis, supernumerary or hypertrophic muscles). Accurate nerve examination must be performed, particularly in patients with atypical ankle pain, to detect focal tenderness or paresthesia. Ultrasonography is useful in this setting because it yields both clinical and morphologic findings. High-resolution magnetic resonance imaging provides accurate delineation of the nervous system anatomy. Furthermore, technologic developments in the field of radiology are making it possible to obtain clearer, more accurate images. Radiologists must be aware of the main nerve entrapment syndromes at the foot and ankle and be able to perform accurate nerve examinations with different imaging modalities in patients with foot and ankle pain.