Peripheral neuropathies of the median, radial, and ulnar nerves: MR imaging features

The median, radial, and ulnar nerves of the upper limbs may be affected by various peripheral neuropathies, each of which may be categorized according to its cause, as either an entrapment or a nonentrapment neuropathy. Entrapment neuropathies, also referred to as nerve compression syndromes, include the supracondylar process syndrome, pronator syndrome, anterior interosseous nerve syndrome, carpal tunnel syndrome, posterior interosseous nerve syndrome, cubital tunnel syndrome, and Guyon canal syndrome. Nonentrapment neuropathies include traumatic nerve injuries, infectious and inflammatory conditions, polyneuropathies, and mass lesions at anatomic locations where entrapment syndromes typically do not occur. Although clinical examination and electrophysiologic testing are the cornerstone of the diagnostic work-up, in certain cases magnetic resonance (MR) imaging may provide key information about the exact anatomic location of a lesion or may help narrow the differential diagnosis. In patients with a diagnosis of peripheral neuropathy, MR imaging may help establish the cause of the condition and provide information crucial for conservative management or surgical planning. In addition, knowledge of the normal anatomy and of the possible causes, typical clinical findings, and MR imaging features of peripheral neuropathies that affect the median, radial, and ulnar nerves allows greater confidence in the diagnosis.