Chapter 6 Spinal Accessory Nerve
Anatomy
• The accessory nerve (cranial nerve XI) leaves the skull through the jugular foramen. Below this landmark the nerve is an immediate anterior relation of the transverse process of the atlas (Figure 6-1).
• The mastoid process is easily palpated, and if the surgeon drops a fingertip immediately below the mastoid a bony prominence may be felt. This is the transverse process of the atlas.
• A line drawn from the transverse process of the atlas to the point of the shoulder overlies the course of the accessory nerve when the neck is viewed from the side (Figure 6-2).
• The nerve runs between the heads of the sternocleidomastoid (SCM) so that it appears to pierce the upper anterior border of that muscle. The sternocleidomastoid is supplied by the nerve before it appears at the posterior border of the muscle. This point is two thirds of the distance between the lower and upper attachments of the SCM.
• As the nerve courses through the posterior triangle, en route to the trapezius, it is covered solely by fascia and skin (Figure 6-3).
• Lymph nodes are characteristically found immediately adjacent to the nerve. Adherence of the two structures may result from previous inflammation.
• The nerve breaks into numerous short branches that directly innervate the great trapezius muscle.
Figure 6-1 The spinal accessory nerve runs obliquely downward and posteriorly across the posterior triangle of the neck, destined for the trapezius muscle.
Figure 6-2 The accessory nerve’s egress from the sternocleidomastoid (SCM) is usually two thirds of the distance between the SCM’s insertion on the clavicle and its origin from the mastoid process.
Figure 6-3 The spinal accessory nerve is covered solely by skin and fascia in the posterior triangle. Lymph nodes are usually close by.
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