Neck Dissection

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CHAPTER 121 Neck Dissection

Key Points

The terms neck dissection and cervical lymphadenectomy refer to the systematic removal of lymph nodes with their surrounding fibrofatty tissue from the various compartments of the neck. This procedure is used to eradicate metastases to the regional lymph nodes of the neck. In most patients, these metastases originate from primary lesions involving mucosal sites of the upper aerodigestive tract, particularly the oral cavity, pharynx, and larynx.

The propensity for spread to the regional lymph nodes by carcinomas of the upper aerodigestive tract is variable and is associated with several factors such as histology, T classification, and location of the primary tumor. For example, if the histology shows perineural invasion or invasion of the tumor’s microcirculation, the risk is higher. In general, the more advanced the T classification, the higher the likelihood of nodal spread. Certain subsites such as the oral tongue, floor of the mouth, piriform sinus, and supraglottic larynx are associated with higher rates of lymphatic metastasis as compared with such subsites as the buccal mucosa, lip, nasal cavity, paranasal sinuses, and glottic larynx. Although the anatomic distribution of the surrounding lymphatic channels may explain some of this variation, inherent differences in the biologic behavior among these cancers are likely as well. Thus the indications for cervical lymphadenectomy depend not only on the presence of palpable disease but on factors that increase the risk of occult disease such as the size and characteristics of the primary tumor. The term therapeutic neck dissection applies to the former condition, whereas the term elective neck dissection applies to the latter situation. Other factors that are important when deciding whether cervical lymphadenectomy is indicated relate to the overall treatment plan. For example, if the treatment of choice for the primary tumor is radiation rather than surgery, it may also be preferable to radiate the regional nodes when the clinical staging of the nodal disease is N0 or N1. If surgical transgression of the regional lymphatics is required to resect the primary tumor, cervical lymphadenectomy should also be included.

Historical Perspective

In publications that came out before the 20th century, little attention was given to the indications or techniques for treating cervical lymph node metastases. The first conceptual approach for removing nodal metastases was made by Kocher in 18801; he described the removal of the lymph nodes located within the contents of the submandibular triangle to gain surgical access to a cancer of the tongue. Later, Kocher recommended that nodal metastases should be removed more widely through a Y-shaped incision, with the long arm extending from the mastoid to the level of the omohyoid at its junction with the anterior border of the sternocleidomastoid muscle. Around the same time, Packard supported the concept of removing the surrounding lymph nodes for lingual cancer.2 The first description of the radical neck dissection was by Jawdynski, a Polish surgeon.3 However, the individual credited the most for developing and reporting the efficacy of this procedure is George Crile.4 Crile believed that distant (hematogenous) metastases were uncommon in head and neck cancer and that metastases more commonly occurred in the neck through the permeation of lymphatics. The descriptions by both of these surgeons of a block resection encompassing all of the cervical nodal groups from the level of the mandible above to the clavicle below became the basis for the radical neck dissection we know today. Relevant to the modifications of radical neck dissection that were subsequently made, Crile recommended preservation of the internal jugular vein and the sternocleidomastoid muscle for patients in whom there were no palpable nodes. In addition, his technique was to remove only the regional lymph nodes that were known to drain the field of the original focus of disease when metastases could not be seen. Also, it is interesting to note that, in the accompanying illustrations of the more radical en bloc resections, the spinal accessory nerve was preserved.

This philosophy of radical en bloc resection based on Crile’s descriptions remained popular with the head and neck surgeons during the first half of the 20th century, in part because of the works of Blair and Brown5 and Martin,6 who were strong proponents of the radical en bloc technique of neck dissection in a manner similar to the radical surgery that had evolved for breast cancer. Martin, in particular, categorically insisted that the spinal accessory nerve, internal jugular vein, and sternocleidomastoid muscle should be removed as part of all cervical lymphadenectomies. It may be useful to remember that, during this time, radiotherapy had not yet been developed as an effective adjuvant modality, and radical surgery represented the only hope for cure.

Associated with the procedure of the radical neck dissection was the presence of significant postoperative morbidity related to shoulder dysfunction; the operation also had limitations as a bilateral procedure.7 In the 1950s Ward and Robben8 reported that the neck dissection could be modified in some circumstances by sparing the spinal accessory nerve and thereby preventing postoperative shoulder drop. Later, Saunders, Hirata, and Jaques9 compared the functional results of cases undergoing radical neck dissection with those in whom the spinal accessory nerve was spared; this demonstrated that shoulder symptoms were only mild or moderate in more than 80% of the patients who had the nerve preserved or cable grafted. The concept of conservation neck surgery was further popularized during the 1960s by Suarez10 in Argentina and promoted by Bocca and Pignataro,11 who independently described an operation that removed all of the lymph node groups while sparing the spinal accessory nerve, sternocleidomastoid muscle, and internal jugular vein. They emphasized that fascial compartments surrounding the lymphatic contents of the neck could be removed without sacrificing the nonlymphatic structures, as mentioned.

Other authors reported the sparsity of nodal disease within the posterior triangle for carcinoma of the oral cavity, pharynx, and larynx, thus setting the stage for modifications directed toward preserving lymph node groups.1215 These observations paved the way for another type of neck dissection modification: one in which there was selective preservation of one or more lymph node groups.1618 Some of the initial proponents of this concept were the surgeons at MD Anderson Cancer Center, who called the procedure “modified neck dissection.”19,20 Two of the variations of the modified neck dissection were also called “supraomohyoid” and “anterior” neck dissections.16 However, the term selective neck dissection (SND) subsequently became associated with the concept of preserving lymph nodes in one or more of the neck levels through the American Academy of Otolaryngology’s classification.17,21 The lymph node groups removed are based on the pattern of metastases, which are predictable relative to the primary site of cancer.

Terminology of Neck Dissection

The evolution of cervical lymphadenectomy procedures during the 20th century has provided the modern head and neck surgeon with a repertoire of surgical techniques for removing nodal metastases. Concurrent with this expansion has been the emergence of a multitude of terms used to describe these procedures. Originally proposed by authors without any uniformity of terminology, this lack of standardization unfortunately resulted in redundancy, misinterpretation, and even confusion among clinicians. Realizing the importance for standardizing the diverse nomenclature, the Committee for Head and Neck Surgery and Oncology of the American Academy of Otolaryngology–Head and Neck Surgery convened a special task force in 1988 to address the problems of terminology related to cervical lymphadenectomy. The specific objectives of the group were as follows: (1) to recommend terminology that adhered to more traditional terms such as “radical” and “modified radical” neck dissection, and to avoid the use of eponyms and acronyms; (2) to define which lymphatic structures and other nonlymphatic structures should be removed or preserved relative to the radical neck dissection; (3) to provide standard nomenclature for the lymph node groups and the nonlymphatic structures; (4) to define the boundaries of resection for lymph node groups; (5) to use terms for the neck dissection procedures that are basic and easy to understand; and (6) to develop a classification on the basis of the biology of the cervical metastases and the principles of oncologic surgery.17

Recently updated by the Committee for Neck Dissection Classification of the American Head and Neck Society (AHNS), the classification is outlined in Table 121-1).9,22,23 The new versions included modifications of the original classification in an effort to remain contemporary and to follow the current philosophy of managing lymph node metastases.

Table 121-1 Types of Neck Dissection

Terminology Definition
Radical Removal of lymph node levels I to V, sternocleidomastoid muscle, spinal accessory nerve, and internal jugular vein.
Modified Removal of lymph node levels I to V (as in radical neck dissection [ND]), but preservation of at least one of the nonlymphatic structures (sternocleidomastoid muscle, spinal accessory nerve, and internal jugular vein).
Selective Preservation of one or more lymph node levels relative to a radical ND.
Extended Removal of an additional lymph node level or group or a nonlymphatic structure relative to a radical ND (muscle, blood vessel, nerve). Examples of other lymph node groups are superior mediastinal, parapharyngeal, retropharyngeal, peri-parotid, postauricular, suboccipital, and buccinator. Examples of other nonlymphatic structures are external carotid artery, hypoglossal, and vagus nerves.

Cervical Lymph Node Groups

The patterns of spread of cancer from various primary sites in the head and neck to the cervical lymph nodes have been documented by retrospective analyses of large series of patients undergoing neck dissection.12,16,24 The nodal groups at risk for involvement are widespread throughout the neck, extending from the mandible and skull base superiorly to the clavicle inferiorly and from the posterior triangle of the neck laterally to the midline viscera and to the contralateral side of the neck. It is now recommended that the lymph node groups in the neck be categorized according to the level system originally described by the Memorial Sloan-Kettering Group (Fig. 121-1).19

There are two important lymph node groups within level I: the submental group and the submandibular group. The submental nodes are defined as those that are contained within the boundaries of the submental triangle (i.e., the anterior belly of the digastric muscles and the hyoid bone). The submandibular lymph node group refers to the nodes lying within the boundaries of the submandibular triangle (i.e., the anterior and posterior bellies of the digastric muscle and the body of the mandible). Because many of these lymph node groups lie in close proximity to the submandibular gland, this structure is removed to ensure thorough exenteration of all of the lymph nodes within this triangle. Thus the boundaries of level I lymph nodes include the body of the mandible, the anterior belly of the contralateral digastric muscle, the posterior belly of the ipsilateral digastric muscle, and the stylohyoid muscle. It should be noted that the perifacial lymph nodes including the buccinator nodes are located outside of this triangle superior to the mandibular body. These nodes may contain metastatic disease when the primary site involved is the lip, buccal mucosa, anterior nasal cavity, or soft tissue of the cheek. Thus the neck dissection performed for nodal disease associated with primary lesions of these sites should be modified to encompass the perifacial nodes.

Level II is defined as the region containing the upper jugular lymph nodes. These are located around the upper third of the internal jugular vein and adjacent to the spinal accessory nerve, extending from the level of the carotid bifurcation (surgical landmark) or hyoid bone (clinical landmark) inferiorly to the skull base superiorly. The lateral boundary is the posterior border of the sternocleidomastoid muscle, and the medial boundary is the stylohyoid muscle. Recently, the AHNS committee recommended that the perpendicular plane defined by the posterior aspect of the submandibular gland could serve as the radiologic landmark for this boundary.

Level III contains the middle jugular lymph node group. These nodes are located around the middle third of the internal jugular vein, extending from the carotid bifurcation superiorly (surgical landmark) or the level of the inferior aspect of the body of the hyoid bone (clinical and radiologic landmark) to the junction of the omohyoid muscle with the internal jugular vein (surgical landmark) or the lower border of the cricoid arch (clinical and radiologic landmark) inferiorly. The lateral boundary is the posterior border of the sternocleidomastoid muscle, and the medial boundary is the lateral border of the sternohyoid muscle. Recently, the AHNS committee recommended that the lateral border of the common carotid artery could serve as the radiologic landmark for the medial boundary.

Level IV contains the lower jugular lymph node group. These nodes surround the lower third of the internal jugular vein, extending from the omohyoid muscle (surgical landmark) or cricoid arch (clinical landmark) superiorly to the clavicle inferiorly. The lateral boundary is the posterior border of the sternocleidomastoid muscle, and the medial or anterior boundary is the lateral border of the sternohyoid muscle. As with level II, the lateral border of the common carotid artery could serve as the radiologic landmark for the medial boundary.

Level V encompasses all lymph nodes contained within the posterior triangle, and these are collectively referred to as the posterior triangle group. The boundaries include the anterior border of the trapezius muscle laterally, the posterior border of the sternocleidomastoid muscle medially, and the clavicle inferiorly. The nodes in this triangle comprise three predominant lymphatic pathways: nodes located along the spinal accessory nerve as it traverses the posterior triangle; nodes located along the transverse cervical artery as it courses along the lower third of the triangle; and the supraclavicular nodes located immediately above the clavicle. The supraclavicular nodes also extend below the level of the upper horizontal border of the clavicle to include one particular node of importance: the sentinel—or Virchow’s—node.

Level VI encompasses the lymph nodes of the anterior compartment of the neck.19,21 This group is made up of nodes that surround the midline visceral structures of the neck, extending from the level of the hyoid bone superiorly to the suprasternal notch inferiorly. On each side, the lateral boundary is formed by the medial border of the carotid sheath. Located within this compartment are the perithyroidal lymph nodes, paratracheal lymph nodes, lymph nodes along the recurrent laryngeal nerves, and precricoid (Delphian) lymph node. These lymph nodes and their connecting lymphatic channels represent pathways of spread from primary cancers originating in the thyroid gland, apex of the piriform sinus, subglottic larynx, cervical esophagus, and cervical trachea.

The superior mediastinal lymph nodes (optionally referred to as level VII) are bounded superiorly by the superior edge of the manubrium, inferiorly by the superior border of the arch of the aorta, and laterally by the common carotid artery on the left side and the innominate artery on the right.

Division of Neck Levels by Sublevels

The 2001 report of the American Head and Neck Society’s Neck Dissection Committee recommended the use of sublevels for defining selected lymph node groups within levels I, II, and V on the basis of the biologic significance, independent of the larger zone in which they lay.21 These are outlined in Figure 121-2 as sublevels IA (submental nodes), IB (submandibular nodes), IIA and IIB (together composing the upper jugular nodes), VA (spinal accessory nodes), and VB (transverse cervical and supraclavicular nodes). The boundaries for each of these sublevels are defined in Table 121-2.

Table 121-2 Lymph Node Groups Found within the Six Neck Levels and the Six Sublevels

Lymph Node Group Description
Submental (sublevel IA) Lymph nodes within the triangular boundary of the anterior belly of the digastric muscles and the hyoid bone; these nodes are at the greatest risk of harboring metastases from cancers arising from the floor of the mouth, anterior oral tongue, anterior mandibular alveolar ridge, and lower lip (see Fig. 121-2).
Submandibular (sublevel IB) Lymph nodes within the boundaries of the anterior belly of the digastric muscle, the stylohyoid muscle, and the body of the mandible, including the preglandular and postglandular nodes and the prevascular and postvascular nodes. The submandibular gland is included in the specimen when the lymph nodes within this triangle are removed. These nodes are at greatest risk for harboring metastases from cancers arising from the oral cavity, the anterior nasal cavity, and the soft tissue structures of the midface and the submandibular gland (see Fig. 121-3).
Upper jugular (sublevels IIA and IIB) Lymph nodes located around the upper third of the internal jugular vein and the adjacent spinal accessory nerve, extending from the level of the skull base above to the level of the inferior border of the hyoid bone below. The anterior (medial) boundary is the stylohyoid muscle (the radiologic correlate is the vertical plane defined by the posterior surface of the submandibular gland), and the posterior (lateral) boundary is the posterior border of the sternocleidomastoid muscle. Sublevel IIA nodes are located anterior (medial) to the vertical plane defined by the spinal accessory nerve. Sublevel IIB nodes are located posterior (lateral) to the vertical plane defined by the spinal accessory nerve. The upper jugular nodes are at greatest risk for harboring metastases from cancers arising from the oral cavity, nasal cavity, nasopharynx, oropharynx, hypopharynx, larynx, and parotid gland (see Fig. 121-3).
Middle jugular (level III) Lymph nodes located around the middle third of the internal jugular vein, extending from the inferior border of the hyoid bone above to the inferior border of the cricoid cartilage below. The anterior (medial) boundary is the lateral border of the sternohyoid muscle, and the posterior (lateral) boundary is the posterior border of the sternocleidomastoid muscle. These nodes are at greatest risk for harboring metastases from cancers arising from the oral cavity, nasopharynx, oropharynx, hypopharynx, and larynx (see Fig. 121-3).
Lower jugular (level IV) Lymph nodes located around the lower third of the internal jugular vein, extending from the inferior border of the cricoid cartilage above to the clavicle below. The anterior (medial) boundary is the lateral border of the sternohyoid muscle, and the posterior (lateral) boundary is the posterior border of the sternocleidomastoid muscle. These nodes are at greatest risk of harboring metastases from cancers arising from the hypopharynx, thyroid, cervical esophagus, and larynx (see Fig. 121-3).
Posterior triangle (sublevels VA and VB) This group is composed predominantly of the lymph nodes located along the lower half of the spinal accessory nerve and the transverse cervical artery. The supraclavicular nodes are also included in the posterior triangle group. The superior boundary is the apex formed by the convergence of the sternocleidomastoid and trapezius muscles; the inferior boundary is the clavicle, the anterior (medial) boundary is the posterior border of the sternocleidomastoid muscle, and the posterior (lateral) boundary is the anterior border of the trapezius muscle. Sublevel VA is separated from sublevel VB by a horizontal plane marking the inferior border of the anterior cricoid arch. Thus sublevel VA includes the spinal accessory nodes, whereas sublevel VB includes the nodes that follow the transverse cervical vessels and the supraclavicular nodes (with the exception of Virchow’s node, which is located in level IV). The posterior triangle nodes are at greatest risk for harboring metastases from cancers arising from the nasopharynx, oropharynx, and cutaneous structures of the posterior scalp and neck (see Fig. 121-3).
Anterior compartment (level VI) Lymph nodes in this compartment include the pretracheal and paratracheal nodes, the precricoid (Delphian) node, and the perithyroidal nodes, including the lymph nodes along the recurrent laryngeal nerves. The superior boundary is the hyoid bone, the inferior boundary is the suprasternal notch, and the lateral boundaries are the common carotid arteries. These nodes are at greatest risk for harboring metastases from cancers arising from the thyroid gland, glottic and subglottic larynx, apex of the piriform sinus, and cervical esophagus (see Fig. 121-2).
Superior mediastinum (optional—level VII) These nodes represent an extension of the paratracheal lymph nodes chain extending inferiorly below the suprasternal notch along each side of the cervical trachea to the level of the innominate artery.

The risk of nodal disease in sublevel IIB is greater for tumors arising in the oropharynx as compared with the oral cavity and larynx.2532 Thus in the absence of clinical nodal disease in sublevel IIA, it is likely not necessary to include sublevel IIB for tumors arising in these latter sites. The dissection of the node-bearing tissue of sublevel IIB (submuscular recess) creates a risk of morbidity. Adequate exposure necessitates significant manipulation of the spinal accessory nerve and may account for trapezius muscle dysfunction observed in a significant minority of patients after an SND. Sublevel IA is a zone from which many surgeons do not remove lymph nodes unless the primary cancer involves the floor of the mouth, the lip, or structures of the anterior midface or there is obvious lymphadenopathy.

Level V is the third region that has been subdivided, into levels VA and VB. The superior component, level VA, primarily contains the spinal accessory lymph nodes, whereas level VB contains the transverse cervical nodes and the supraclavicular nodes, which carry a more ominous prognosis when positive in cases with upper aerodigestive tract malignancies.

Correlation of Neck Level Boundaries with Anatomic Markers Depicted Radiologically

Radiologists have now identified landmarks that more accurately identify the location of lymph nodes according to the level system (Table 121-3).33,34 Using radiologic landmarks, level I includes all of the nodes above the level of the lower body of the hyoid bone, below the mylohyoid muscles, and anterior to a transverse line drawn on each axial image through the posterior edge of the submandibular gland. Level IA represents those nodes that lie between the medial margins of the anterior bellies of the digastric muscles, above the level of the lower body of the hyoid bone, and below the mylohyoid muscle (these were previously classified as submental nodes). Level IB represents the nodes that lie below the mylohyoid muscle, above the level of the lower body of the hyoid bone, posterior and lateral to the medial edge of the ipsilateral anterior belly of the digastric muscle, and anterior to a transverse line drawn on each axial image tangent to the posterior surface of the submandibular gland on each side of the neck (these are also referred to as submandibular nodes). Level II extends from the skull base at the lower level of the bony margin of the jugular fossa to the level of the lower body of the hyoid bone. Level II nodes lie anterior to a transverse line drawn on each axial image through the posterior edge of the sternocleidomastoid muscle, and they lie posterior to a transverse line drawn on each axial scan through the posterior edge of the submandibular gland. However, any nodes that lie medial to the internal carotid artery (ICA) are retropharyngeal and thus not level II.

Level III nodes lie between the level of the lower body of the hyoid bone and the level of the lower margin of the cricoid cartilage. These nodes lie anterior to a transverse line drawn on each axial image through the posterior edge of the sternocleidomastoid muscle. Level III nodes also lie lateral to the medial margin of either the common carotid artery or the ICA. On each side of the neck, the medial margin of these arteries separates level III nodes, which are lateral, from level VI nodes, which are medial.

Thus the revised classification uses the horizontal plane defined by the inferior border of the hyoid bone instead of the carotid bifurcation to delineate the boundary between levels II and III. Similarly, the revised classification uses the horizontal plane defined by the inferior border of the cricoid cartilage instead of the junction between the superior belly of the omohyoid muscle to delineate the boundary between levels III and IV. However, from a surgical perspective, it is important to note the significance of the anatomic relationship between the omohyoid muscle and the internal jugular vein because lymph nodes are usually located in this region. These nodes would be included in level III.

Neck Dissection Classification

The classification for neck dissection recommended by the American Head and Neck Society’s committee is based on the following rationale: (1) that radical neck dissection is the standard basic procedure for cervical lymphadenectomy, and all other procedures represent one or more modifications of this procedures; (2) when the modification of the radical neck dissection involves the preservation of one or more nonlymphatic structures, the procedure is called modified radical neck dissection; (3) when the modification involves the preservation of one or more lymph node groups that are routinely removed in the radical neck dissection, the procedure is called SND; and (4) when the modification involves the removal of additional lymph node groups or nonlymphatic structures relative to the radical neck dissection, the procedure is called extended radical neck dissection (see Table 121-1).

A “planned” neck dissection is typically performed 6 to 8 weeks after the completion of radiotherapy or chemoradiotherapy when the chance of residual disease in the neck is high. Some centers use 18F-fluorodeoxyglucose positron emission tomography (PET) scan to further decide whether to perform a neck dissection. Because the reliability of a PET scan is questionable before 3 months have passed following completion of radiation or chemoradiation, a “planned” neck dissection based on the results of this investigation may have to be deferred until this time.

As opposed to a planned neck dissection, a “salvage” neck dissection is performed when metastatic disease in the neck occurs after it has been treated previously. The salvage neck dissection can be further classified as “early” procedure when it is done for persistent disease after chemo/radiation or “late” when it is done for recurrent disease.

Technique

FLAP ELEVATION

The initial incision is carried through skin and platysma muscle, although the platysma is deficient in the midline and the lateral-most parts of the incision. This anatomic feature can be used to reapproximate the flaps at the time of closure because the platysmal muscle edges serve as “natural hash marks.” The flap is raised in the subplatysmal plane so that the external jugular vein and the greater auricular nerves are not included in the flap (Fig. 121-5A). Although these structures will ultimately be sacrificed in the radical neck dissection, in SND procedures, they are routinely preserved. When there is gross pathologic evidence of tumor extension through the platysma muscle, with or without skin involvement, the area of disease involvement should also be removed and modifications of the skin flap may be required. Identification of the mandibular branch of the facial nerve is performed after complete elevation of the skin flaps superiorly and inferiorly to expose all of the lymph node levels of the neck. It is recommended that the anterior facial vein be ligated and retracted superiorly to protect this nerve only after the superior skin flap is raised. This allows proper assessment of the prevascular and postvascular lymph nodes in the submandibular triangle, which will need to be removed. Therefore it is best to incise the submandibular fascia at the lower border of the submandibular gland and to carefully raise this fascia off of the submandibular gland superiorly to the level of the lower border of the mandible as a separate flap. Usually the mandibular branch of the facial nerve may be seen as this fascia is raised (see Fig. 121-5B).

DISSECTION OF THE POSTERIOR TRIANGLE

The subsequent order of dissection is a matter of individual preference, although there is some oncologic rationale for dissecting from below upward rather than from above downward. Thus the next step is to expose the anterior border of the trapezius muscle from its superior aspect, where it converges with the posterior border of the sternocleidomastoid muscle, to its inferior aspect, where it approaches the clavicle (see Fig. 121-5C). The fibrofatty tissue is then incised along its anterior border beginning superiorly and working inferiorly to expose the muscular floor of the posterior triangle. In so doing, the spinal accessory nerve will be severed at the point at which it enters the trapezius muscle in the lower aspect of the posterior triangle. After this step has been completed, the floor of the posterior triangle at its inferior extent is next exposed by incising through the fibrofatty tissue immediately above the superior border of the clavicle. This requires incising through the inferior belly of the omohyoid muscle and the fibrofatty tissue overlying the brachial plexus. In this region, the transverse facial artery will be encountered immediately overlying the muscular floor of the triangle; this artery should be preserved unless there is gross disease involving the region. The fibrofatty contents of the posterior triangle are then mobilized anteriorly, lifting them away from the floor of the neck, which, in this region, is formed by the splenius capitis, levator scapulae, and scalene muscles. It is important to remain superficial to the prevertebral fascia during this step of the operation to prevent injury to the phrenic nerve and the brachial plexus. As the fibrofatty tissue is swept in a lateral-to-medial direction, the sensory branches of the cervical plexus will be encountered and divided.

ANTERIOR TRIANGLE DISSECTION

As the fibrofatty tissue is elevated medially toward the carotid sheath, it will be necessary to incise the mastoid attachment of the sternocleidomastoid muscle and the clavicular attachments (see Fig. 121-5D). The carotid sheath will be exposed, and identification of the common carotid artery and vagus nerve may be made. Attention should be given to preserving the cervical sympathetic chain, which is closely applied to the prevertebral fascia behind the carotid sheath. The plane of dissection will be carried between the vagus nerve and the carotid artery below and the internal jugular vein above. Thus the internal jugular vein may be mobilized from the skull base superiorly to its inferior aspect near the clavicle; ties may then be placed around the upper and lower ends of the internal jugular vein, thereby allowing ligation and complete mobilization. When incising the soft tissue contents of the lower medial aspect of the neck, lymphatic channels will be encountered, particularly on the left side. It is imperative to precisely identify these and ligate them immediately as they are encountered. The thoracic duct is located to the right of and behind the left common carotid artery and the vagus nerve. From here, it arches upward, forward, and laterally, passing behind the internal jugular vein and in front of the anterior scalene muscle and the phrenic nerve; it then opens into the internal jugular vein, subclavian vein, or angle formed by the junction of these two vessels. The duct is anterior to the thyrocervical trunk and the transverse cervical artery. To prevent a chyle leak, the surgeon should also remember that the thoracic duct may be multiple in its upper end and that, at the base of the neck, it usually receives the jugular trunk, a subclavian trunk, and maybe other minor lymphatic trunks that should be individually divided and ligated or clipped.

After ligation of the lower part of the internal jugular vein, the contents of the mobilized specimen are retracted superiorly and medially. Dissection is carried along the common carotid artery and medially as far as the sternohyoid muscle. Further elevation of the contents exposes the carotid bifurcation. As this is done, the branches of the internal jugular vein require identification and ligation. Specifically, these are the middle and superior thyroid veins and the retromandibular vein. Further superior elevation of the fibrofatty contents away from the upper part of the carotid sheath exposes the hypoglossal nerve lying lateral to the external carotid artery and the spinal accessory nerve extending from above downward.

At this point, the posterior belly of the digastric muscle is identified, and the soft tissue attachments of the neck contents lying superior to the muscle are divided, including the sternocleidomastoid muscle as it attaches to the mastoid process, vascular channels extending into the postauricular region and parotid gland, the tail of the parotid gland that extends downward inferior to the level of the digastric muscle, and soft tissue attachments to the angle of the mandible. After completion of this part of the dissection, all of the lower contents of the neck dissection specimen should be freely mobile, and the only remaining attachments are the upper end of the internal jugular vein and the undissected contents of the submandibular triangle and the submental triangle (see Fig. 121-5E).

DISSECTION OF THE UPPER NECK COMPARTMENTS

Excision of level I lymph nodes is begun by dividing the soft tissue overlying the body of the mandible including the facial artery and vein as they emerge above the submandibular gland and extend lateral to the body of the mandible. The anterior bellies of the ipsilateral and contralateral digastric muscles are skeletonized, thereby delineating the boundaries of the submental triangle. After the fibrofatty tissue has been removed from occupying this space, the fibrofatty contents of the anterior portion of the submandibular triangle are removed from the underlying mylohyoid muscle until its lateral border may be identified. The lateral border of the muscle is then retracted anteriorly, exposing the deep contents of the submandibular triangle. This allows for visualization of the lingual nerve, submandibular duct, and hypoglossal nerve. The submandibular duct is isolated, divided, and ligated. Next, the submandibular ganglion should be divided, thus allowing the lingual nerve to retract superiorly away from the area of dissection. Care is taken to not injure the hypoglossal nerve and its venae comitantes in the deep portion of the triangle. The last attachment of the contents of the submandibular triangle is the proximal end of the facial artery as it courses deep to the submandibular gland. It is important to remember that complete excision of all contents of the submandibular triangle within its muscular boundaries—and not just the submandibular gland—is required.

Variations in the approach to the radical neck dissection should be made, depending on the location of the disease and its degree of mobility. For example, it is best to mobilize the areas that are least involved with a tumor that is difficult to remove, which will enhance the exposure of the anatomic structures that may be directly invaded by the disease itself.

Neck drains are inserted and brought through separate stab incisions through the most dependent areas of the dead space. Closure of the incisions are usually performed in two layers, including approximation of the platysma anteriorly and the subcutaneous tissue laterally and the second layer approximating the skin.

Modified Radical Neck Dissection

DEFINITION

A modified radical neck dissection is defined as the en bloc removal of lymph node–bearing tissue from one side of the neck (levels I to V). The dissection extends from the inferior border of the mandible above to the clavicle below and from the lateral border of the strap muscles medially to the anterior border of the trapezius muscle laterally. Unlike the radical neck dissection, there is preservation of one or more of the following structures in the modified radical dissection: spinal accessory nerve, internal jugular vein, and sternocleidomastoid muscle (Fig. 121-6). The major purpose of these modifications relates to the morbidity encountered when the spinal accessory nerve is removed. Although the degree of morbidity is less for removal of the sternocleidomastoid muscle and the internal jugular vein, this issue becomes far more important if bilateral neck dissections are required. Simultaneous sacrifice of both internal jugular veins may result in severe swelling of the face with increased intracranial pressure.

TECHNIQUE

Knowledge of the surgical anatomy of the spinal accessory nerve is essential to preserve this structure. Below the jugular foramen, the spinal accessory nerve is located deep to the digastric and stylohyoid muscles and lateral or immediately posterior to the internal jugular vein; it then runs obliquely downward inferiorly and posteriorly to reach the medial surface of the sternocleidomastoid muscle near the junction of the superior and middle third. It traverses this muscle, giving off a major branch to it. The remaining part of the nerve then exits the posterior border of the sternocleidomastoid muscle near the area known as Erb’s point, where the four superficial branches of the cervical plexus—the greater auricular, lesser occipital, transverse cervical, and supraclavicular nerves—emerge from behind the muscle. This point is located approximately at the junction of the upper and middle thirds of this muscle. From here, the spinal accessory nerve courses through the posterior triangle of the neck to enter the anterior border of the trapezius muscle at a point located approximately at the junction of the middle and lower thirds of the anterior border of this muscle.

The incisions and skin flaps are raised for modified radical neck dissection as similarly described for the radical neck dissection. The same procedure is followed to identify and protect the mandibular branch of the facial nerve in level I.

Unlike what is found in the radical neck dissection procedure, the next step is to identify the spinal accessory nerve. This is initially done in the posterior triangle from which the nerve exits at or around Erb’s point (Fig. 121-7A). The nerve lies superficially in the fibrofatty contents of the posterior triangle and usually may be identified by careful spreading of the fibrofatty tissue; the use of a nerve stimulator may assist this process. Once located, the nerve is isolated and dissected away from the underlying fibrofatty contents from Erb’s point medially to the point at which it enters the anterior border of the trapezius muscle laterally (see Fig. 121-7B). The nerve is next isolated in its superior third, which is done by incising the anterior border of the sternocleidomastoid muscle from its attachment superiorly at the mastoid to its lowermost attachment at the sternal head. The sternocleidomastoid muscle is retracted laterally as the fibrofatty soft tissue contents anterior to this muscle are dissected away from it, and the many arcades of small blood vessels coursing between the muscle and the soft tissue are divided. This part of the procedure mobilizes the anterior aspect of the sternocleidomastoid muscle along its full extent. As the muscle is retracted laterally in its upper portion, the spinal accessory nerve is seen entering its deep surface (see Fig. 121-7C

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