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 directly on CT, so standardized methods use nearby anatomy — the scalene muscles and the subclavian/axillary vessels — as guides. The Hall method (developed in head and neck patients) is the most widely used; the Kong thoracic atlas covers it for chest cases. Timmerman 2022 Tables 8–11 include a contouring instruction for the plexus as well. Sources commonly define the plexus per side — for example, Timmerman 2022 Table 1 names the ipsilateral plexus.