Role of high-resolution ultrasound and magnetic resonance neurography in the evaluation of peripheral nerves in the upper extremity

Ali Serhal1, Steven Kyungho Lee1, Julia Michalek2, Muhamad Serhal1, Imran Muhammad Omar1

Affiliation and address for correspondence
J Ultrason 2023; 23: e313–e327
DOI: 10.15557/JoU.2023.0037
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Upper extremity entrapment neuropathies are common conditions in which peripheral nerves are prone to injury at specific anatomical locations, particularly superficial regions or within fibro-osseous tunnels, resulting in pain and potential disability. Although neuropathy is primarily diagnosed clinically by physical examination and electrophysiology, imaging evaluation with ultrasound and magnetic resonance neurography are valuable complementary non-invasive and accurate tools for evaluation and can help define the site and cause of nerve dysfunction which ultimately leads to precise and timely treatment. Ultrasound, which has higher spatial resolution, can quickly and comfortably characterize the peripheral nerves in real time and can evaluate for denervation related muscle atrophy. Magnetic resonance imaging on the other hand provides excellent contrast resolution between the nerves and adjacent tissues, also between pathologic and normal segments of peripheral nerves. It can also assess the degree of muscle denervation and atrophy. As a prerequisite for nerve imaging, radiologists and sonographers should have a thorough knowledge of anatomy of the peripheral nerves and their superficial and deep branches, including variant anatomy, and the motor and sensory territories innervated by each nerve. The purpose of this illustrative article is to review the common neuropathy and nerve entrapment syndromes in the upper extremities focusing on ultrasound and magnetic resonance neurography imaging.

ultrasound; upper extremity; magnetic resonance neurography; nerve compression
Video 1. Use of the elevator technique to assess the median nerve in a 48-year-old male asymptomatic subject using 24 MHz linear transducer. The nerve is first identified in the short axis in the carpal tunnel, where it is superficial and easily seen. Then, keeping the transducer in the short axis with respect to the nerve, the nerve is tracked proximally within the forearm as it courses between the heads of the pronator teres muscle, where the nerve may be more difficult to see given its deeper and more curved course. This technique allows complete identification of the nerve in the territory of interest and gives the nerve anatomic context to assess its relationships to surrounding structures and identify muscle atrophy or fatty infiltration
Video 2. 43-year-old female with ulnar neuropathy, particularly when flexing the elbow. Dynamic assessment of the ulnar nerve using 24 MHz linear transducer initially shows the nerve is located within the cubital tunnel when the elbow if extended. However, when the patient actively flexes the elbow, the nerve snaps over the medial humeral epicondyle, which produces paresthesias along the ulnar margin of the forearm and the small and ring fingers