What does the radial tunnel look like on ultrasound?

Under normal ultrasound imaging, the radial nerve and the “tunnel” of structures surrounding it can be visualized in the short-axis view across the anterior upper forearm. 

Look for the hyperechoic/bright dome of the radial head at the bottom “floor” of the image and then the hypoechoic supinator muscle curving over the top of the bone (there are two muscle “heads”). The radial nerve resembles a bright hyperechoic oval with a honeycomb texture sitting within or just above the supinator. 

The brachioradialis muscle above forms the “ceiling” of the tunnel over the radial nerve, the extensor carpi radialis longus and brevis muscles laterally, and the brachialis medially. 

Technically speaking, radial tunnel syndrome describes the entrapment of the deep branch of the radial nerve as it passes between the superficial and deep heads of the supinator muscle. Immediately after the nerve exits the supinator, it is called the posterior interosseous nerve. However, any or all surrounding myofascial structures can cause nerve compression, leading to symptoms.

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