MR imaging of entrapment neuropathies at the elbow Marcelo Bordalo-Rodrigues, MD, Zehava Sadka Rosenberg, MD * Hospital for Joint Diseases, 301 East 17th Street, New York, NY 10003, USA The median, ulnar, and radial nerves are susceptible to many compressive neuropathies at the elbow and proximal forearm. The diagnosis is usually based on clinical history and examination [1–3]. Electrodiagnostic studies may help to corroborate clinical diagnosis. However, clinical signs and nerve conduction studies can be non- specific and may not correlate with each other. Also, multiple compression sites often coexist simultaneously and simulate other pathologic conditions, further confounding the clinical diagnosis. MR imaging is effective in the assessment of peripheral nerve disorders. There are, however, no large, controlled studies to determine the accuracy of MR imaging in detection of nerve compression in the elbow. The major roles of MR imaging include evaluating nerve involvement, detecting external processes causing mass effect and nerve compression, identifying muscle denervation pat- terns, and excluding other pathologic conditions that may mimic or coexist with compressive neuropathies at the elbow. Following review of the normal anatomy of the median, ulnar, and radial nerves at the elbow, this article focuses on compressive neuropathies at the elbow and the role of MR imaging in their diagnosis. Anatomy Median nerve The median nerve arises from the lateral and medial cords of the brachial plexus (C6–T1), coursing down the arm medial to the biceps muscle and anterior to the brachial artery. In the elbow region, the nerve courses anterior to the brachialis muscle and posterior to the lacertus fibrosus (bicipital aponeurosis). It enters the forearm between the two heads of the pronator teres muscle and courses distally between the flexor digitorum superficialis and flexor digitorum profundus muscles, maintaining this relationship throughout its course in the forearm (Fig. 1) [4–6]. In the proximal forearm, the median nerve supplies the flexor pronator group of muscles originating from the medial epicondyle. These include the pronator teres, the flexor carpi radialis, the palmaris longus, and the flexor digitorum superficialis muscles. It also provides branches to the elbow and proximal radioulnar joints, a branch to the palmar skin, and muscular branches to the thenar eminence. The anterior interosseous nerve is the largest branch of the median nerve, arising approxi- mately 5 to 8 cm distal to the level of the lateral epicondyle and coursing over the interos- seous membrane toward the wrist. It is considered a purely motor nerve and supplies the deep ventral muscles of the forearm, including the radial half of the flexor digitorum profundus, the flexor pollicis longus, and the pronator quadratus muscles. Ulnar nerve The ulnar nerve is formed by the medial cord of the brachial plexus (C8 and T1). It courses medial to the axillary and brachial arteries until the midarm. At this level, the nerve pierces the medial intermuscular septum and enters the posterior compartment. Approximately 8 cm proximal to the medial epicondyle, the nerve may pass under a fibrous tunnel called arcade of * Corresponding author. E-mail address: zehava.rosenberg@med.nyu.edu (Z.S. Rosenberg). 1064-9689/04/$ - see front matter Ó 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.mric.2004.02.002 Magn Reson Imaging Clin N Am 12 (2004) 247–263