Note the massive enlargement, hypoechogenicity, and loss of fascicular structure of the median nerve. Neuromuscular ultrasound done a few weeks after showed a pseudoaneurysm of the brachial artery just proximal to the antecubital fossa, exerting pressure on the median nerve ( Fig. EMG showed a severe median neuropathy at or proximal to the take-off to the PT muscle.
Afterward, she had near paralysis of all muscles supplied by the median nerve. During the procedure, she developed severe pain down the forearm into the median-innervated digits. A 33-year-old woman with end-stage kidney disease on dialysis had an attempted cannulation of her fistula just proximal to the antecubital fossa. 21.8).Įxample 2: Traumatic Pseudoaneurysm. Neuromuscular ultrasound showed an enlarged and hypoechoic median nerve just proximal to the antecubital fossa, with additional hypoechoic tissue surrounding the median nerve, representing either edema or acute hematoma ( Fig. Nerve conduction studies showed absent median motor and sensory responses with EMG evidence of active denervation in the FPL and PT, consistent with a proximal median neuropathy. Dense sensory loss was present in the entire median nerve distribution. He had persistent weakness of thumb flexion, thumb abduction, and flexion of digits 2 and 3. He underwent closed reduction and percutaneous pin fixation. A 6-year-old boy fell and sustained a supracondylar fracture of the distal humerus. Several examples of different structural lesions affecting the proximal median nerve, diagnosed by neuromuscular ultrasound, follow.Įxample 1: Supracondylar fracture. Lastly, in chronic lesions, the pattern of denervation atrophy in different muscles can add information regarding the location of the nerve lesion. Bone spurs are recognized by their marked hyperechoic reflection and prominent posterior acoustic shadowing. In the rare case of a supracondylar spur resulting in a ligament of Struthers entrapment, one looks for a bone spur arising from the medial distal humerus. When assessing vascular structures, the color and/or power Doppler must be used. In addition, one of the major advantages of ultrasound is its ability to visualize structural lesions, including ganglion cysts, scarring, aneurysms, vascular anomalies/injuries, and tumors ( Fig. As in other entrapment neuropathies, the proximal median nerve should be assessed for its size, echogencity, and fascicular structure. When assessing for proximal median neuropathy, after scanning the median nerve at the wrist, the ultrasound probe should be used to scan from the mid-forearm to mid-arm. In others, the median nerve is more medial, located over the proximal edge of the PT. In most individuals, the median nerve and brachial artery are immediately adjacent to each other. As it nears the surface, it runs under the lacertus fibrosus accompanied by the brachial artery, which is just lateral. It then runs between the two heads of the PT with the large humeral head above it and the small ulnar head below ( Fig. The nerve is deepest at this location and more difficult to visualize. It then moves proximally through the FDS, where it exits under the tendinous arch of the sublimis bridge.
As the probe is moved proximally, the median nerve is joined by the ulnar artery. Recall that in the mid-forearm, the median nerve is easily visualized with ultrasound as it runs in the fascial plane between the FDS and FDP. Preston MD, in Electromyography and Neuromuscular Disorders, 2021 Proximal Median Nerve
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