Dissection Of The Spinal Accessory Nerve

The dissection of the spinal accessory nerve is one of the few steps of the operation that we usually perform using scissors instead of scalpel. To approach this area the sternocleidomastoid muscle is retracted posteriorly, and the posterior belly of the digastric muscle is pulled superiorly with a smooth blade retractor (Fig. 4-26). The wet surgical sponges previously left over the nerve at the level of its entrance in the sternocleidomastoid muscle are removed and the nerve is dissected toward the carotid sheath.

At this level the nerve runs within the ''lymphatic container'' of the neck, thus forcing the surgeon to cut across the fibrofatty tissue instead of following fascial planes as for the rest of the operation. Consequently, the tissue overlying the nerve is divided and the nerve completely exposed from the sternocleidomastoid muscle to the internal jugular vein (Fig. 4-27).

As the dissection approaches the internal jugular vein, the surgeon must be aware of the relations between these two structures. Usually, the internal jugular vein lies immediately behind the proximal portion of the nerve. However, on some occasions the nerve may go behind the

Figure 4-26 Surgical field prepared for the dissection of the spinal accessory area on the right side of the neck. SC, Sternocleidomastoid muscle; IJ, Internal jugular vein; sa, spinal accessory nerve; hn, hypoglossal nerve; mn, marginal mandibular branch of the facial nerve; fv, facial vein; SG, submandibular gland; pg, tail of the parotid gland; F, fascia dissected form the upper part of the surgical field.

Figure 4-26 Surgical field prepared for the dissection of the spinal accessory area on the right side of the neck. SC, Sternocleidomastoid muscle; IJ, Internal jugular vein; sa, spinal accessory nerve; hn, hypoglossal nerve; mn, marginal mandibular branch of the facial nerve; fv, facial vein; SG, submandibular gland; pg, tail of the parotid gland; F, fascia dissected form the upper part of the surgical field.

Figure 4-27 The spinal accessory nerve is completely exposed in the upper part of the field on the right side of the neck. sa, spinal accessory nerve; IJ, internal jugular vein; oa, occipital artery; SC, Sternocleidomastoid muscle; , fibrofatty tissue of the upper jugular and upper spinal accessory regions.

Figure 4-27 The spinal accessory nerve is completely exposed in the upper part of the field on the right side of the neck. sa, spinal accessory nerve; IJ, internal jugular vein; oa, occipital artery; SC, Sternocleidomastoid muscle; , fibrofatty tissue of the upper jugular and upper spinal accessory regions.

vein or even across it (Fig. 4-28). These anatomical variations should be kept in mind to avoid unintentional damage to the internal jugular vein when following the spinal accessory nerve.

Once the spinal accessory nerve has been completely exposed, the tissue lying superior and posterior to the nerve must be dissected from the splenius capitis and levator scapulae muscles. The tissue is pulled in an anteroinferior direction toward the spinal accessory nerve.

It must be emphasized that the lymph nodes that are now being removed are located between the spinal accessory nerve and the internal jugular vein. This region corresponds to the ill-defined boundary between area II and the upper part of area V, which constitutes one of the weak points of the artificial lymph nodal region classification. The lymph nodes in this region belong to the spinal accessory nerve lymph chain and to the upper jugular lymph chain, and no clear anatomical landmarks can be found here to separate these two lymphatic chains (Fig. 4-29). Thus, the surgeon

Accessory Nerve Ijv Relation
Figure 4-28 Anatomic relations between the spinal accessory nerve and the internal jugular vein.

Figure 4-29 Posterior retraction of the sternocleidomastoid muscle distorts the theoretic limits between level II and the upper part of level V on an area without significant anatomic landmarks. The dotted lines show the variability of the boundaries between these two levels (right side).

must be especially careful during this step of the operation to avoid missing potentially metastatic lymph nodes behind.

The occipital and sternocleidomastoid arteries are often found at this step of the operation (Fig. 4-27). When seen, they must be ligated and divided. However, most of the time they are inadvertently sectioned during the removal of the lymphatic tissue in this area. If this happens it is usually easier to cauterize them instead of trying to place clamps and ligatures.

Once the dissected tissue reaches the level of the spinal accessory nerve it must be passed underneath the nerve to be removed in continuity with the main part of the specimen. Osvaldo Suarez referred to this step of the operation as ''the spinal accessory maneuver'' (Figs. 4-30, 4-31). After this maneuver has been completed, the specimen includes the fibrofatty tissue coming from the spinal accessory nerve area along with the tissue removed from the submandibular triangle (area I) and upper jugular region (Fig. 4-32).

Before moving to the next step of the operation, a final cut is made in this area that will help further dissection. Keeping the sternocleidomastoid muscle retracted posteriorly, a number 10 scalpel blade is used to make an incision into the tissue located below the entrance of the spinal accessory nerve into the sternocleidomastoid muscle. This cut is made just anterior to the sternocleidomastoid muscle and goes down to the level of Erb's point following the medial border of the sternocleidomastoid muscle (Fig. 4-33). The underlying levator scapulae muscle is identified and the tissue is slightly dissected forward and medially over its fascia. The rest of the dissection in this area will be completed later.

Again, wet surgical sponges are left around the spinal accessory nerve over the splenius capitis and levator scapulae muscles, and the dissection is taken to the supraclavicular fossa.

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