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.