Various pathologic conditions extending from the lumbar and pelvic regions to the lower leg may manifest as foot drop, or weakness of ankle dorsiflexion. Potential causes of foot drop include L5 radiculopathy, lumbosacral plexopathy, sciatic neuropathy, and peroneal neuropathy. Although the first-line test in lesion localization is most commonly electrodiagnostic testing, MR neurography has emerged as a useful tool to verify lesion site, to accurately characterize the cause of the neuropathy, and to guide patient treatment. MR neurography, when tailored and focused, can help overcome potential pitfalls in clinical and electrodiagnostic evaluation and is commonly performed in the authors' practice. MR neurography studies are protocoled in advance after careful review of clinical notes and electrodiagnostic findings and often after discussion with the referring clinician. Radiologists who interpret MR neurography studies should have a sound understanding not only of peripheral nerve anatomy and common pathologic conditions, but also of the clinical and electrodiagnostic evaluation performed in patients with foot drop. In this way, the radiologist can actively guide the referring clinician in ordering the most appropriate imaging examination, efficiently reaching the correct diagnosis, and deciding appropriate treatment.
