Position the patient in the semi-Fowler (modified beach chair) position with a shoulder roll. Tuck the arms on both sides with padding. If a previous scar is present, as is often the case in patients with thyroid cancer, use this incision and extend it several
centimeters to the ipsilateral side. Extend the incision vertically along the border of the trapezius muscle to create a hockey stick incision. A variety of alternative incision options exist including making a counter incision along the angle of the mandible (McFee) or making an incision along the angle of the mandible and continuing inferiorly with or without extension along the clavicle (Crile and Martin incisions, respectively).
Create subplatysmal flaps superiorly and inferiorly and place a small spring retractor in the incision for exposure. As the skin extension is carried superiorly, so too the flaps will be extended above the superficial fascia.
Two common variations involve preservation of the spinal accessory nerve (Fig. 11.8A) or SCM (Fig. 11.8B). To preserve the SCM where it meets the lateral border of the strap muscles, separate the SCM off of the strap muscles with either cautious electrocautery usage or a combination of sharp and blunt dissection with silk ties. Mobilize the entire SCM. When the sternal border of the SCM has been fully mobilized, retract the SCM laterally and the strap muscles medially. Identify the omohyoid muscle and retract it laterally. Alternatively, some surgeons divide the omohyoid muscle.
Figure 11-8 Modified Radical Neck Dissection (From Bailey BJ, Johnson JT, eds. Head & Neck Surgeryâ
!”Otolaryngology. 4th ed. Philadelphia: Lippincott Williams & Wilkins; 2006:1594â!“1595, with permission.)
As you mobilize the sternal border of the SCM laterally, the internal jugular vein will come into view. Start in the lowest visualized portion of the neck (level IV) and begin dissecting the thin fibrofatty tissues off of the internal jugular vein. Carry the dissection inferiorly to the level of the clavicle and then return superiorly to dissect to the level of the mandible (level II). Be cautious to identify internal jugular branches and lymphatic channels as you continue your dissection, because these will need to be ligated with ties. As you progress superiorly, the spinal accessory nerve will come into view and will need to be carefully preserved.
Finally, retract the SCM laterally to allow for resection of the level V nodal tissues.
Take the fatty tissues between the reflected SCM to the border of the trapezius with sharp dissection. Complete the dissection by resecting level VI nodes as described in the Central Node Dissection section if these have not been previously resected.
Obtain meticulous hemostasis. Place a drain along the full aspect of the incision and bring it out inferiorly. Approximate the platysma and then close the skin.
Anatomic Points
The definition of a modified radical neck dissection varies by authors, but generally involves dissection of levels II through VI (or II through V when a previous central neck dissection has been performed). It differs from the now-obsolete radical neck dissection
P.90 in that it spares the SCM, internal jugular vein, and spinal accessory nerve. The borders of the dissection are the posterior belly of the digastric muscle superiorly, the spinal accessory nerve posterolaterally, and thoracic inlet inferiorly.
The platysma is innervated by the cervical branch of the facial nerve. The nerve courses inferiorly deep to the platysma, with anterior branches supplying the platysma. The skin incision and the subsequent elevation of the myocutaneous flaps will, of necessity, denervate all or part of the platysma. The vertical limb of the incision almost approximates the course of the external jugular vein, lying immediately deep to the platysma muscle. This vein crosses the superficial surface of the SCM, passing inferiorly from its beginning into the parotid gland to just lateral to the clavicular attachment of the SCM where it joins the subclavian vein.
Several nerves are at risk or intentionally ligated during creation of the flaps and dissection of the SCM. During creation of the skin flaps, dissection along the ramus of the mandible reveals the mandibular branch of the facial nerve. It is located about 2 to 3 cm below the facial artery and vein at the tail of the parotid gland. This nerve innervates the muscles of the lower lip and chin. Injury to the nerve can result in significant functional and cosmetic losses. Ligation of the facial vein at this level allows the mandibular branch to be retracted superiorly with the subplatysmal flap, reducing injury risk during neck dissection. Branches of the great auricular nerve, a sensory
branch of the cervical plexus bearing fibers from C2 and C3, will be severed during exposure of the upper attachment of the SCM. Branches of the transverse cervical nerve, a sensory branch of the cervical plexus that also carries fibers of C2 and C3, will be divided with the incision as well.
The inferior limb of the incision is relatively risk free. The supraclavicular nerves (sensory divisions of the cervical plexus carrying fibers of C3 and C4) that supply the skin of the lower neck and extend onto the upper thorax will be encountered and must be cut. The sensory branches of the cervical plexus all emerge from under the middle of the SCM and fan out from this point. Those that supply regions anterior to the SCM cross the superficial surface of that muscle. Several superficial veins will also be encountered deep to the platysma and should be ligated.
The omohyoid muscle has two bellies. The inferior belly passes almost horizontally from its origin on the upper border of the scapula to the intermediate tendon (attached by a fascial sling to the medial ends of the clavicle and first rib), which intervenes between the SCM and the internal jugular vein. The superior belly passes superiorly, and almost vertically, to its attachment on the greater conus of the hyoid. The inferior belly lies immediately superficial to the supraclavicular part of the brachial plexus, suprascapular and transverse cervical vessels, and phrenic nerve, which lies on the anterior scalene muscle.
Below the reflected omohyoid muscle lie the transverse cervical vessels, which need to be carefully ligated and divided. The phrenic nerve, crossed superficially by the vessels, must be identified and preserved. It lies deep to the lateral branches of the
thyrocervical trunk and superficial to the anterior scalene muscle and is the only longitudinal structure coursing superolaterally to inferomedially in the lower neck.
The medial dissection requires an understanding of the relationships of the structures
within the carotid sheath. Just above the medial end of the clavicle, the internal jugular vein is anterolateral, the common carotid artery is anteromedial, and the vagus nerve is posterior in the groove between these two vessels. As the internal jugular vein is exposed, the middle thyroid vein should be identified, ligated, and divided; this vein, which is present in about half of cases, will be encountered at about the level of the lower and middle third of the thyroid gland. It passes anterior to the common carotid artery.
On the left side, the thoracic duct enters the neck by passing along the left side of the esophagus. It arches (as much as 3 to 4 cm superior to the clavicle) anterior to the thyrocervical trunk, phrenic nerve, and medial border of the anterior scalene muscle and posterior to the left common carotid artery, vagus nerve, and internal jugular vein.
From the apex of this arch, the duct descends anterior to the left subclavian artery. It may empty into the junction of the subclavian vein and internal jugular vein or into either of these great veins near their junction, or it may divide into smaller vessels before terminating. On the right, typically three major lymphatic trunks (right
subclavian, right jugular, and right bronchomediastinal trunks) terminate independently on the anterior aspect of the jugulosubclavian junction, the internal jugular vein, the subclavian vein, or any combination of these. If these lymphatic vessels are injured, they should be ligated to prevent development of a chylous fistula.
The sympathetic chain lies immediately posterior to the carotid sheath. As with the phrenic nerve, it lies deep to prevertebral fascia and should be protected. Other than the vagus nerve, which is of substantial size and must be preserved, the only other nerves that should be encountered while dissecting the carotid sheath form its contents are the descendens hypoglossi (typically located on the anterior surface of the carotid sheath) and the descendens cervicalis (generally, lateral or medial to the internal jugular vein and thus in the lateral wall of the sheath or emerging through the anterior wall). These anastomose to form the ansa cervicalis, which as previously mentioned, innervates the strap muscles. These nerves may need to be sacrificed, but the descendens hypoglossi should be identified because it leads the surgeon back to the hypoglossal nerve. Other nerves that might be encountered during this dissection include the recurrent laryngeal nerve and, much higher, the superior laryngeal nerve.
These nerves are described in more detail in Chapter 6.
The superior portion of the dissection is the most challenging because many structures are present in a relatively small space. In the case of radical neck dissections or head and neck cancer, submandibular glands (level I) will be excised. Excision of the submandibular glands necessitates ligation and division of their duct (Wharton duct).
This duct extends anteriorly from the deep surface of the gland in the interval between the more superficial mylohyoid muscle and the deeper hypoglossal muscle. Here, it lies between the more inferior hypoglossal nerve and the lingual nerve. As the lingual nerve passes forward deep to the mylohyoid muscle, it passes lateral to the duct, gently curves inferiorly, and finally terminates on the medial aspect of the duct by giving off terminal branches. Close to the posterior border of the mylohyoid muscle, preganglionic parasympathetic secretomotor fibers diverge from the lingual nerve to synapse with postganglionic fibers in the submandibular ganglion. Postganglionic fibers provide parasympathetic innervation to the submandibular gland; thus, traction of the gland can stretch the lingual nerve. Because of these anatomic relations, it is necessary to skeletonize the submandibular gland gently before ligated and dividing it to ensure that
P.91 these important nerves are preserved.
The fascia investing the SCM, or the investing layer of the deep cervical fascia, also invests the trapezius muscle and that part of the spinal accessory nerve that passes from the SCM to the trapezius muscle. Division of this nerve causes significant disability because elevation, rotation, and retraction of the scapula are all affected, and atrophy of the trapezius muscle presents difficulties when a cervical collar is used. As the spinal accessory nerve passes posteriorly, it usually (in 70% of cases) crosses superficial to the internal jugular vein, although in 27% of cases it passes deep to the jugular vein. It innervates the SCM 4 cm or more inferior to the tip of the mastoid, and then either pierces or passes deep to that muscle to innervate the trapezius muscle.