Neuromuscular ultrasound in clinical practice: A review

Abstract

Neuromuscular ultrasound (NMUS) is becoming a standard element in the evaluation of peripheral nerve and muscle disease. When obtained simultaneously to electrodiagnostic studies, it provides dynamic, structural information that can refine a diagnosis or identify a structural etiology. NMUS can improve patient care for those with mononeuropathies, polyneuropathy, motor neuron disease and muscle disorders. In this article, we present a practical guide to the basics of NMUS and its clinical application. Basic ultrasound physics, scanning techniques and clinical applications are reviewed, along with current challenges.

Keywords: CIDP; Carpal tunnel syndrome; Myopathy; Neuromuscular ultrasound; Peripheral neuropathy; Ulnar neuropathy.

Fig. 1

Cross-sectional (a) and longitudinal (b) views of a normal median nerve (MN). Note the “honey-comb” appearance of the cross-sectional view and the surrounding hyperechoic epineurium seen in both views.

Fig. 2

Cross-sections of the median nerve (MN) and underlying flexor tendons (ft). When the transducer is angled, the median nerve remains similar in echogenicity whereas the flexor tendons demonstrate the principle of anisotropy as their appearance changes depending on the angle of the transducer (a and b). Similarly, a cross-section of tibialis anterior muscle demonstrates alternating echogenicity with tilting of the transducer in the two sections of muscle separated by an aponeurosis (c and d). Hypoechoic bone shadow is seen on the bottom left corners (B).

Fig. 3

Cross-sectional views of a normal median nerve (asterisk) at the wrist (a) compared to a hypoechoic, flattened, enlarged median nerve in a patient with carpal tunnel syndrome, with a CSA measuring 17 mm² (b). Common anatomical variants include bifid median nerve (MN) (c) and a persistent median artery (PMA), seen by doppler (d).

Fig. 4

A cross-sectional view of a normal median nerve (MN) when imaged at the distal wrist crease, lying above the flexor digitorum tendons (ft) in the carpal tunnel (a). For evaluation of carpal tunnel, the CSA at the wrist should be compared to the CSA in the mid-forearm (b).

Fig. 5

Cross-sectional views of the ulnar nerve (UN) at the wrist (a), forearm (b), cubital tunnel (d), and epicondylar groove (d). UA: ulnar artery, P: pisiform bone, FDS: flexor digitorum superficialis muscle, FCU: flexor carpi ulnaris muscle, FDP: flexor digitorum profundus muscle. Demonstration of patient positioning for evaluation of the ulnar nerve at the elbow (e).

Fig. 6

Cross-sectional views of the radial nerve (RN) above the elbow (a) and at the bifurcation into the deep branch of the radial nerve (D) and superficial branch of the radial nerve (S). MeHT: medial head of the triceps brachii, LoHT: long head of the triceps brachii, LaHT: lateral head of the triceps brachii.

Fig. 7

Cross-sectional (a) and longitudinal (b) views of the fibular nerve (PN) just above the fibular head. Probe placement for the cross-sectional view at the fibular head is demonstrated on the top left corner.

Fig. 8

Cross-sectional view of the plantar nerves (PTN) within the tarsal tunnel. PTT: posterior tibial tendon, FDL: flexor digitorum longus tendon, PTA: posterior tibial artery, Medial Mall: medial malleolus, FHL: Flexor hallucis longus.

Fig. 9

Cross-sectional view of the radial nerve (RN) at the level of the mid-humerus in a patient with radial nerve palsy following a comminuted fracture of the humerus. The radial nerve here is focally enlarged (21 mm²) and surrounded by fibrosis.

Fig. 10

View of the common carotid artery (CCA), internal jugular vein (IJV), and vagus nerve (arrow) beneath the sternocleidomastoid (SCM) (a). Confirmation of vessel location by doppler is demonstrated in the bottom left corner (b).

Fig. 11

The C5 nerve arises from anterior (AT) and posterior (PT) tubercles that resemble a molar tooth (a). The C6 nerve root arises from a prominent anterior tubercle, resembling a “thumbs up” sign (b). C7 transverse process lacks an anterior tubercle but has a posterior tubercle that resembles the back of a chair (c). The nerve roots can be seen exiting their foramina in a sagittal view (d). The transducer positioning is demonstrated by the black line. The roots and proximal trunks can be seen between the anterior and middle scalene muscles (e). Further laterally, the plexus appears as a “bunch of grapes” (f). SCM: sternocleidomastoid muscle, CA: carotid artery, AS: anterior scalene muscle, MS: middle scalene muscle, SA: subclavian artery.

Fig. 12

Cross-sectional (a) and longitudinal (b) views of a normal tibialis anterior muscle.

Fig. 13

Normal increase in diaphragm thickness (double-headed arrows) from expiration (a) to inspiration (b). Ext. Intercostal m.: External intercostal muscle, Int. Intercostal m.: Internal intercostal muscle.

Fig. 14

The lateral cutaneous nerve of the thigh (N) passing under the inguinal ligament (IL) and above the iliacus at the level of the anterior superior iliac spine (ASIS).