Sonographic Pearls for Imaging the Brachial Plexus and Its Pathologies

Abstract

The brachial plexus (BP) is a complicated neural network, which may be affected by trauma, irradiation, neoplasm, infection, and autoimmune inflammatory diseases. Magnetic Resonance Imaging is the preferred diagnostic modality; however, it has the limitations of high cost and lack of portability. High-resolution ultrasound has recently emerged as an unparalleled diagnostic tool for diagnosing postganglionic lesions of the BP. Existing literature describes the technical skills needed for prompt ultrasound imaging and guided injections for the BP. However, it remains particularly challenging for beginners to navigate easily while scanning its different parts. To address this, we share several "clinical pearls" for the sonographic examination of the BP as well as its common pathologies.

Keywords: brachial plexus; injury; neck; nerve; sonography.

Figure 1

Overview of the brachial plexus on the cadaveric model after removal of the anterior scalene muscle (A). Schematic drawing of the brachial plexus anatomy (B). The roots, trunks, divisions, cords (C), and terminal branches (D) of the brachial plexus in the cadaveric models. 1: suprascapular nerve; 2: musculocutaneous nerve; 3: axillary nerve; 4: radial nerve; 5: medial brachial cutaneous nerve; 6: median nerve; 7: ulnar nerve; 8: intercostobrachial cutaneous nerve. AS: anterior scalene muscle; MS: middle scalene muscle; CCA: common carotid artery; ICA: internal carotid artery; IJV: internal jugular vein; SCA: subclavian artery; SV: subclavian vein; SSA: suprascapular artery; ST: superior trunk; MT: middle trunk; IT: inferior trunk; Pma: pectoralis major muscle; Pmi: pectoralis minor muscle; X: vagus nerve. Yellow arrowhead: phrenic nerve.

Figure 2

Ultrasound imaging of the brachial plexus. It resembles a bunch of grapes, situated posterior to the subclavian artery (A). The C5 anterior ramus is seen in its short-axis (B) and long-axis (C) views. In some variants, the C5 anterior ramus (yellow arrowhead) may course anterior to the anterior scalene muscle instead of the inter-scalene groove (D). AS: anterior scalene muscle; AT: anterior tubercle; IJV: internal jugular vein; MS: middle scalene muscle; PT: posterior tubercle; SCA: subclavian artery; SCM: sternocleidomastoid muscle; TP: transverse process; VA: vertebral artery. The yellow dashed area encircles the brachial plexus and the blue rectangles at the bottom-right corners represent the transducer position.

Figure 3

The C7 transverse process usually has only one posterior tubercle. In certain cases, a rudimentary anterior tubercle (white arrowhead) can be visualized (A). The costal tubercle (black arrowhead) on the first rib may be mistaken as the posterior tubercle of the transverse process (B). Swapping the transducer posteriorly to validate the first costotransverse joint (white arrow) helps differentiating the first rib from the C7 transverse process (C). AS: anterior scalene muscle; LOC: longus colli muscle; MS: middle scalene muscle; PT: posterior tubercle; TP: transverse process; VA: vertebral artery. The yellow dashed area encircles the brachial plexus and the blue rectangle represents the transducer position.

Figure 4

Schematic drawing (A), X-ray imaging (B) and ultrasound images (C) of the cervical rib (white arrows). AS: anterior scalene muscle; CR: cervical rib; MS: middle scalene muscle; TP: transverse process. The yellow dashed area encircles the brachial plexus.

Figure 5

Ultrasound imaging of the C8 and T1 anterior rami. The C8 anterior ramus (A) is seen on top of the pleura at the bottom of the inter-scalene groove. T1 anterior ramus (B) can be visualized distal and lateral to the inter-scalene groove, emerging from the undersurface of the first rib. AS: anterior scalene muscle; MS: middle scalene muscle; SCA: subclavian artery; SCM: sternocleidomastoid muscle. White arrowheads: superior trunk; Yellow arrowheads: middle trunk. The blue rectangles at the bottom-right corners represent the transducer position.

Figure 6

The transverse cervical artery, thyrocervical trunk, suprascapular artery and nerve (A), as well as the course and relevant vasculature of the vertebral artery (B) in a cadaver model. 1: suprascapular artery; 2: suprascapular nerve; 3: superior trunk; 4: transverse cervical artery; 5: subclavian artery; 6: anterior scalene muscle; 7: phrenic nerve; 8: inferior thyroid artery; 9: thyrocervical trunk. CCA: common carotid artery; ICA: internal carotid artery; VA: vertebral artery. Red numbers indicate arteries, while the white numbers indicate nerves and muscles.

Figure 7

Doppler ultrasound imaging of the transverse cervical artery, thyrocervical trunk (A), suprascapular artery and nerve (B), vertebral artery (C), and radicular artery (D). AP: articular pillar; AS: anterior scalene muscle; CCA: common carotid artery; IT: inferior trunk; LOC: longus colli muscle; LS: levator scapulae muscle; MT: middle trunk; OMH: omohyoid muscle; SCA: subclavian artery; SCM: sternocleidomastoid muscle; ST: superior trunk; SUA: suprascapular artery; TCA: transverse cervical artery; VA: vertebral artery. Yellow arrowhead: suprascapular nerve; Red arrowhead: radicular artery. The yellow dashed area encircles the brachial plexus, and the blue rectangles in the bottom-right corners represent the transducer position.

Figure 8

The long thoracic and dorsal scapular nerves cadaveric models. 1: dorsal scapular nerve; 2: long thoracic nerve; 3 phrenic nerve; 4: vagus nerve. AS: anterior scalene muscle; CCA: common carotid artery; IJV: internal jugular vein; MS: middle scalene muscle; ST: superior trunk.

Figure 9

The dorsal scapular nerve (black arrowhead) emerges from the C5 anterior ramus, pierces the medial scalene muscle (A) and further courses underneath the levator scapulae muscle (B). The long thoracic nerve (white arrowhead) also travels inside the middle scalene muscle (C). The suprascapular nerve (yellow arrowhead) branches from the superior trunk of the brachial plexus (D). AS: anterior scalene muscle; LS: levator scapulae muscle; MS: middle scalene muscle; PS: posterior scalene muscle; SCM: sternocleidomastoid muscle; ST: superior trunk; SA: serratus anterior muscle. The blue rectangles at the bottom-right corners represent the transducer position.

Figure 10

Ultrasound imaging of radiation-induced brachial plexopathy. Nerve fascicles of the brachial plexus at the root (A) and trunk (yellow dashed area) (B) levels appear enlarged with thickened epineurium. The muscles surrounding the neck are atrophic and fibrotic in the short-axis (C) and long-axis (D) views. AS: anterior scalene muscle; MS: middle scalene muscle; SCM: sternocleidomastoid muscle; ST: superior trunk.

Figure 11

Ultrasound imaging of metastatic brachial plexopathy. The nerve fascicles (yellow dashed area) at the trunk level (A) and intertubercular groove (B) are enlarged secondary to the tumor infiltration. Like elsewhere, side-to-side comparison is contributory. AS: anterior scalene muscle; MS: middle scalene muscle; OMH: omohyoid muscle; SCA: subclavian artery.

Figure 12

Ultrasound imaging of metastatic brachial plexopathy. The nerves (yellow arrowheads) are enlarged (A) with intra-neural hypervascularity (B). In the long-axis view, segmental swelling of the nerves (yellow arrowheads) are seen at the supraclavicular (C) and infraclavicular (D) levels. CLA: clavicle; SCA: subclavian artery.

Figure 13

Ultrasound imaging of the suprascapular nerve (black arrowheads) in a patient with Parsonage-Turner syndrome (A). The normal nerve (white arrowhead) on the contralateral side (A). The enlarged suprascapular nerve in the long-axis view (B), atrophy and fat infiltration of the supraspinatus and infraspinatus muscles (C) are also seen. OMH: omohyoid muscle; SCA: subclavian artery. The yellow dashed area encircles the brachial plexus.

Figure 14

Schematic drawing of different types of nerve injury (A). Ultrasound imaging of chronic traumatic brachial plexus injury: a neuroma (red dashed area) (B) and tethered brachial plexus (yellow dashed area) besides the scar (white dashed area) (C). AS: anterior scalene muscle; SCA, subclavian artery.

Figure 15

Ultrasound imaging of thoracic outlet syndrome caused by subclavian artery compression in a young woman suffering right arm pain during inspiration. Ultrasound images during expiration (A) and inspiration (B) showed sudden narrowing of the subclavian artery during inspiration (red dashed area). Focal stenosis of the subclavian artery was not obvious in the magnetic resonance angiography during right arm elevation (C). Inferior trunk: yellow dashed area. AS: anterior scalene muscle; SCA: subclavian artery.