Brachial Plexus

A network of nerves formed from the ventral rami of C5–T1. It passes between the anterior and middle scalene muscles, over the first rib and under the clavicle into the axilla, traveling alongside the subclavian and then axillary vessels.

The nerves that run from the neck into the arm. They control the muscles of the shoulder, arm and hand and carry feeling back from them.

Injury causes brachial plexopathy — pain, weakness or numbness in the arm — which can be permanent. In lung, it matters most for apical (superior sulcus) tumors and for supraclavicular nodal targets. In SBRT tables it is treated as a serial structure with a point-dose limit. In head and neck treatment it lies next to the lower neck nodal levels (IV and V), so it is evaluated whenever the lower neck is treated; target coverage usually takes priority.

The plexus is hard to see on CT, so Brouwer 2015 defines it by the anatomy around it (Table 1):

• Top: the top of the C5 vertebral body.
• Bottom: the top of the T3 vertebral body.
• Front: the back edges of the anterior scalene muscle, the subclavian artery and the axillary vein.
• Back: the front edges of the middle scalene, serratus anterior and subscapularis muscles.
• Outside: the outer edges of the anterior and middle scalene muscles, the pectoralis major and the teres major.
• Inside: the intervertebral foramen (bony vertebral body) and the outer edge of the first rib.

On the lowest slices, where the plexus wraps around the vessels, the vessels are included in the contour. Brouwer's supplement gives a step-by-step technique based on the Hall 2008 method. Sources commonly define the plexus per side.