Imaging of peripheral nerve lesions in the lower limb.

Lower limb peripheral neuropathy may have a variety of causes. This article focuses on focal neural lesions because of neural entrapment associated with static mechanical compression or dynamic compression/stretching. Mechanical compression may relate to direct blunt trauma, surgical injury, mass effect associated with adjacent mass lesions, and frictional effects associated with fibrous bands. Stretching neural injury may be associated with abnormalities in alignment such as plano-valgus hindfoot and hindfoot pronation. Recurrent inversion ankle injuries may also cause neural injury. Neural injury may be associated with denervation of the muscles supplied by the nerve. Electromyography (EMG) remains the gold standard for diagnosis of denervation. Diagnostic imaging plays a complementary role to EMG in difficult cases, the anticoagulated patient, and in clarifying the etiology of an EMG-demonstrated neuropathy. Magnetic resonance imaging and ultrasound can be used in peripheral nerve imaging to demonstrate extrinsic compressive lesions, focal neural lesions such as neural edema and swelling, focal neural scarring (posttraumatic neuroma in continuity) and intraneural ganglia. Imaging can also demonstrate the effects of muscle denervation. Focal areas of tenderness can be highlighted using skin markers for magnetic resonance imaging and by transducer palpation on ultrasound. Ultrasound can be particularly useful in assessing for intrinsic lesions in small peripheral nerves because of the superior spatial resolution of ultrasound in assessing superficial structures. Plain x-rays (and sometimes computed tomography scanning) may show significant bone changes and should be the initial imaging modality.