Mauricio A. Moreno
Abstract
A modified radical neck dissection is defined as functional resection of the lymphatic levels I to V in the neck. This procedure was pioneered by Suarez and Bocca, who were the first to understand the concept of nodal groups defined by fascial places during the second half of the last century. This operation revolutionized the practice of head and neck oncology, and laid the foundation for the development of ever less invasive approaches, even decades after its inception. In this chapter, critical aspects of the surgical anatomy of the neck are reviewed, and the reader is presented with strategies to avoid common pitfalls in the execution of the procedure.
Keywords: neck dissection, modified, functional, technique, complications.
7.1 Introduction
The concept of neck dissection refers to systematic resection of lymph nodes from well-defined fascial compartments in the neck. These will be, the vast majority of times, performed in the context of mucosal aerodigestive tract, salivary, cutaneous, or endocrine malignancies. The oncologic rationale for the procedure involves resecting lymph nodes that show clinical or radiological evidence of involvement (clinically positive necks or cN +) or are at risk of harboring microscopic disease (clinically negative necks or cN0). As such, depending on the clinical neck status, neck dissections are classified as therapeutic for patients with cN + and as elective or prophylactic in patients with cN0. Throughout its more than 100 years of history, neck dissection has continuously evolved from a mutilating radical surgery to an elegant, anatomically bound ablation with minimal functional impact. Similarly, as it relates to the nomenclature and indications, the last decades have seen a significant degree of consolidation that has laid the foundation for a common understanding of its oncological and technical aspects.
The current nomenclature for the boundaries and contents of the nodal groups in the neck is summarized in Table 7.1 and illustrated in Fig. 7.1. A modified radical neck dissection, which is the most comprehensive form of functional neck dissection, entails the resection of the nodal groups I through V, and is still considered the standard of care for management of the cN + neck. The width and scope of this surgery mandate a polished surgical technique and thorough knowledge of the anatomy. While this surgery can be analyzed from multiple perspectives, this chapter will primarily focus on its anatomical and technical aspects, which are essential to perform this surgery safely, effectively, and efficiently. As such, it is strongly recommended that the reader reviews Chapter 3 to get intimately familiar with the surgical anatomy of the neck.
Table 7.1 Contents and boundaries of the lymphatic levels of the neck.23
|
Level |
Content and boundaries |
|
Level I (submental and submandibular) |
The lymph nodes between the mandible and hyoid bone. The posterior (lateral) boundary is the vertical plane defined by the posterior edge of the submandibular gland. This level is divided into two sublevels. |
|
Sublevel IA (submental) |
The lymph nodes within the triangular boundary of the anterior belly of the digastric muscles and the hyoid bone. |
|
Sublevel IB (submandibular) |
The lymph nodes within the boundaries of the anterior belly of the digastric muscle, the stylohyoid muscle, and the body of the mandible. The submandibular gland is usually included within the specimen when the lymph nodes of this triangle are removed. |
|
Level II (upper jugular) |
The lymph nodes located around the upper third of the internal jugular vein and spinal accessory nerve, extending from skull base to the level of the inferior border of the hyoid bone. The anterior (medial) boundary is the vertical plane defined by the posterior edge of the submandibular gland and the posterior (lateral) boundary is the posterior border of the sternocleidomastoid muscle. |
|
Sublevel IIA |
The lymph nodes located anterior (medial) to the spinal accessory nerve. |
|
Sublevel IIB |
The lymph nodes located posterior (lateral) to the spinal accessory nerve. |
|
Level III (middle jugular) |
The 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. |
|
Level IV (lower jugular) |
The lymph nodes located around the lower third of the internal jugular vein extending form 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. |
Continued
Table 7.1 continued
|
Level Level V (posterior triangle group) |
Content and boundaries 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 formed by 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. This level is also divided at the level of anterior cricoid arch into sublevels VA and VB. |
|
Sublevel VA |
Contents of level V above the level of anterior cricoid arch. |
|
Sublevel VB |
Contents of level V below the level of anterior cricoid arch. |
|
Level VI (anterior compartment group or central group) |
The pretracheal and paratracheal nodes, 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. |
|
Level VII (upper mediastinal group) |
Contains the paratracheal lymph nodes and fibrofatty tissue located between the suprasternal notch and the innominate artery. |
Fig. 7.1 Lymphatic group levels of the neck.
7.1.1 History and Classification
Historically, the first accounts of nodal resection for treatment of cancers date back to the 19th century, with Kocher and Packard describing the removal of cervical lymph nodes as treatment of oral cavity cancers. FranciszekJawdynski is credited with the first description of a radical neck dissection in the Polish literature in 1888. However, George Crile was the surgeon who popularized the technique and established its oncologic rationale and indications.1 In his description of radical neck dissection, Crile advocated for en bloc resection of cervical nodes and the internal jugular vein (IJV), sternocleidomastoid muscle (SCM), and spinal accessory nerve (SAN). The procedure was widely adopted and endorsed by prominent head and neck surgeons such as Vilray Blair and Hayes Martin and became the standard of care for neck management through the first half of the 20th century. In the second half of the 20th century, most of the modifications to the procedure were aimed at limiting morbidity, ushered by Ward, who described a SAN-sparing approach to neck dissection in 1951. This trend toward less radical procedures was fueled by further understanding of the fascial boundaries of the neck compartments, which led to the description of a comprehensive neck dissection sparing the SAN, IJV, and SCM by Suarez in 1963, which he named functional neck dissection.2 It was Boc- ca and Pignataro,3 however, who was largely responsible for disseminating and promoting the technique in the United States and Europe. The next incremental steps in the evolution of this procedure became possible thorough a more thorough understanding of the patterns for nodal spread depending on the location of the primary tumor.4 This ushered in the concept of selective neck dissections, which only address the nodal basins at risk and spare other lymphatic groups, and largely reducing perioperative morbidity. Although these were initially implemented in the context of the cN0 neck, they are more commonly being used for treatment of cN +. As it relates to the classification of the procedure, the current nomenclature has not changed since 2002 (Table 7.2) and modified radical neck dissection formally entails the resection of all lymphatic groups in the neck (I-V) with preservation of the IJV, SAN, and SCM. This procedure is still the standard of care in the management of the cN + neck, although there is growing evidence supporting the role of selective approaches in this setting as well. Given the low rate of involvement of level V, this level is commonly spared, yielding to the common practice among head and neck surgeons of colloquially calling a selective neck dissection of levels I to IV, a modified radical neck dissection. The history and the evolution of the procedure are reviewed in detail in Chapter 2.
7.2 Surgical Technique
The following section describes a step-by-step approach for the dissection of neck levels I to V in a sequential fashion. Decision points and critical aspects of the surgical anatomy will be addressed as the process is described, with the intention of contextualizing the information within the flow of the operation. For the same reason, intraoperative images were preferred over diagrams whenever possible. From the perspective of a practicing head and neck surgeon, the importance of having a systematic approach to the neck cannot be overemphasized, and this chapter has been written with that goal in mind. In this author’s experience, this consistency will reward practitioners with a level of confidence, and familiarity with the anatomy, that will prove essential when clinical judgment calls for an alternative surgical approach.
As it relates to the decision-making process before and during the operation, there are countless valid variations in planning and execution that truly epitomize the art of surgery. A such, the information presented by no means represents an exclusive view of this operation, but rather a compendium of collective knowledge and personal experience, validated over years of academic practice.
7.2.1 Patient Positioning
Once the airway is secured, the bed is routinely turned 90 to 180 degrees. Before placing a shoulder roll, the neck is inspected in the supine position under gently anterior flexion to identify and mark the location of skin creases. A shoulder roll is then placed at the level of the scapulas in order to gently lift the superior chest and neck. Care must be taken to ensure the head is not hanging, especially in older patients. The head must be supported with a soft device that holds it in position, such as a donut-shaped gel cushion. While the procedure can be performed in straight supine position, the best exposure is achieved in beach chair position, elevating the back of the table about 30 degrees, and gently lowering the legs. The head is extended and rotated to the opposite side; this maneuver not only provides the best exposure, but also brings the relevant anatomical structures to a more horizontal plane, significantly facilitating the dissection (Fig. 7.2).
At this point, inspection and palpation are used to identify landmarks in surface anatomy such as the angle of the mandible, suprasternal notch, and mastoid tip. The neck can be gently flexed to identify natural skin creases, which should also be marked.
Table 7.2 Past and current classifications of neck dissection24
|
1991 classification |
2002 classification |
2008 update |
|
Radical neck dissection |
Radical neck dissection |
Classification and terminology of neck |
|
Modified radical neck dissection |
Modified radical neck dissection |
dissection has not changed. New recommenda- |
|
Selective neck dissection • Supraomohyoid • Lateral • Posterolateral • Anterior |
Selective neck dissection: each variation is depicted by “SND” and the use of parentheses to denote the levels or sublevels removed |
tions: • Boundaries between levels I and II, and levels III/IV and VI • Terminology of the superior mediastinal nodes (level VII) |
|
Extended neck dissection |
Extended neck dissection |
• The method of submitting surgical specimens for pathologic analysis |
|
(Committee for Head and Neck Surgery and Oncology of the American Academy of Otolaryngology-Head and Neck Surgery) |
(American Head and Neck Society and Committee for Head and Neck Surgery and Oncology, American Academy of Otolaryngology-Head and Neck Surgery) |
(American Head and Neck Society and Committee for Head and Neck Surgery and Oncology, American Academy of Otolaryngology-Head and Neck Surgery) |
Fig. 7.2 Patient positioning.
7.2.2 Incision Placement
The placement of the surgical incisions for a neck dissection can have a profound impact on access, perioperative morbidity, and reconstructive considerations. During the evolution of neck dissection, many surgical approaches have been described (Fig. 7.3) and are associated with the pioneers of the procedure. Nowadays, most of these approaches are seldom performed. As the collective knowledge has matured, a more utilitarian approach is overwhelmingly favored by most surgeons; as such, modern-day incisions are usually apron-type or transversal incisions at a skin crease.
The factors that must be considered for surgical planning are the following:
• Skin flap viability.
• Appropriate access to nodal groups of interest.
• Cosmetic outcome.
• Reconstructive needs (need for skin resection/rotational flaps).
• Reoperative exposure (risk of ipsilateral or contralateral neck recurrence).
Of these, skin flap viability is perhaps the most important consideration, and is affected by many factors, most of them outside the control of the surgeon (previous neck radiation or surgery, malignant cutaneous extension, vasculopathy). Regardless of the chosen approach, some common considerations are helpful in minimizing the risk of flap failure:
• Skin flaps must be broad based to maximize blood supply.
• Flap elevation should be in the subplatysmal plane and limited to the areas of oncologic interest.
• Trifurcate incisions should be avoided whenever possible.
• Placement of secondary limb incisions should consider the risk of carotid exposure.
• Preoperative planning is essential when performing cervicalbased rotational flaps for reconstruction (i.e., platysma or submental flaps).
In terms of flap viability, the platysma plays an important role in neck dissections. The muscle covers the vast majority of the anterior neck, and it has a rich blood supply that originates primarily from the submental artery, with tributaries from the superior thyroid, occipital, and posterior auricular arteries.5 For this reason, incorporating this muscle in the flaps maximizes blood supply to the overlying skin, thus significantly decreasing the risk of flap loss. This muscle is also important as it defines the appropriate fascial layers of the procedure. The platysma is enveloped by the superficial cervical fascia; elevating the skin flaps in the plane immediately deep to it will preserve the integrity of the superficial layer of the deep cervical fascia (SLDCF; considered the superficial boundary of the dissection).
There are some situations that mandate flap elevation in a supraplatysmal plane. These include cases where there is concern for involvement of the muscle by the disease process, such as extracapsular nodal extension, or when a myocutaneous platysma flap is considered for reconstructive purposes. While it has been largely replaced by other reconstructive options, the myocutaneous platysma flap should be part of the armamentarium of every head and neck surgeon, as it provides an elegant alternative for closure of small to medium sized intraoral defects, especially in patients with significant comorbidities. In a recent literature review, Eckard reported a flap success rate ranging from 71 to 100%6 and concluded that most failures were related to history of previous radiation or ligation of the facial artery. From the technical standpoint, patient selection and surgical planning are of outmost importance if this flap is to be attempted. The flap can be harvested as a superiorly or posteriorly based island flap (Fig. 7.4). Superiorly based flaps have the advantages of an increased arc of rotation, robust arterial supply, and capability of sparing the cervical branch of the facial nerve, while posteriorly based flaps have better venous drainage. Regardless of the chosen approach, these flaps must be marked preoperatively, and they dictate the location of the rest of the incisions for the neck dissection. In a similar fashion, submental rotational flap and cervicofacial flaps require thoughtful preoperative consideration when planning for incision placement.
Fig. 7.3 Neck incisions for modified radical neck dissection. (a) Hockey stick or half-apron. (b) Boomerang. (c) MacFee. (d) Modified Schobinger. (e) Apron or bilateral hockey stick.
Fig. 7.4 (a) Superiorly based platysma flap. (b) Inferiorly based platysma flap.
Fig. 7.5 Initial elevation of the subplatysmal flap. EJV, external jugular vein; GAN, greater auricular nerve.
7.2.3 Exposure: Skin Flap Elevation
Anatomically, a modified radical neck dissection requires wide exposure of the anterior and posterior neck triangles, so the boundaries for skin flap elevation are the mandibular margin and tail of parotid superiorly, the clavicle inferiorly, the strap muscles medially, and the anterior border of the trapezius muscle posteriorly.
Once the incision placement has been decided, the skin is incised with Bovie electrocautery and the incision is taken through the subcutaneous tissue and platysma, carefully avoiding violating the fascial layer below. Alternatively, the skin incisions may be performed with scalpel, prior injection with diluted lidocaine and epinephrine. At this point, skin flaps are elevated in the subplatysmal plane wide enough to expose all the anatomical landmarks and provide access to the nodal groups of interest. This is a relatively avascular plane that is only intermittently pierced by cutaneous perforators, so flaps can be raised with sharp instrumentation or with Bovie electrocautery (Fig. 7.5). For this reason, the rate of bleeding can be used as a surrogate for appropriateness of the surgical plane: if bleeding is significant, the skin flaps are likely being raised in the wrong plane (usually too deep).
In the midline, the platysma has a variable degree of dehiscence, and fibers that decussate in the submental area. For this reason, it is recommended that for patients undergoing bilateral neck dissection, lateral flaps are elevated first and subsequently addressing the anterior neck, once the correct plane has been established. If an apron skin flap is used for access, the superior elevation should not go above the level of the mandible, as there is risk to damage the lower branches of the facial nerve. Inferiorly, the skin flaps should be elevated to the level of the clavicles, although this plane can be extended into the anterior chest for reconstructive purposes, such as a cervicothoracic flap. This maneuver completes the skin flap elevation over the anterior triangle (Fig. 7.6).
Fig. 7.6 Completed elevation of the skin flaps over the anterior triangle. EJV, elevated jugular vein; GAN, greater auricular nerve; SCM, sternocleidomastoid muscle; SMG, submandibular gland.
Posteriorly, the platysma extends roughly to the level of the external jugular vein or slightly beyond it, so elevating the skin flaps beyond this boundary is significantly more challenging. The external jugular vein can also be used as a landmark; since the SLDCF invests the SCM and the vein, the plane of dissection is immediately superficial to the vessel. The same is true for other veins of the superficial plexus, such as the anterior jugular veins. On a technical point, if the external jugular vein is injured to the point that requires ligation, the stumps must be maintained in the same anatomical plane (i.e., attached to the SCM) and not elevated with the skin flaps, a common mistake among neophyte surgeons.
Similarly, posterior to the platysma, cranial sensory nerves (greater auricular, lesser occipital, and transverse cervical) traverse over the SCM and are invested in the SLDCF, so they are reliable points of reference as the surgical plane is immediately superficial to them. This same surgical plane must be maintained as flap elevation proceeds over the posterior triangle. This is significantly more challenging in this area as there no consistent points of reference, so it is recommended to frequently compare the skin flap thickness to the anterior flaps. In terms of elevation of skin flaps, in the posterior triangle there is also risk of injury of the SAN. The nerve is exposed to injury along its entire course in this area as it has a very superficial location and it is only protected by a thin fascial layer. Flap elevation with electrocautery may lead to abrupt nerve stimulation (especially in the coagulation setting), causing a violent trapezius contraction that brings the tissue toward the instrument, posing an exceptional risk. Furthermore, this may happen even if the patient is fully paralyzed. As such, it is recommended that this portion is performed with scalpel or with the electrocautery in a low intensity, pure cut setting.
To fully expose the contents of level V, it is often necessary to drop an accessory limb from the main incision; ideally, this limb must merge with the main incision at a 90-degree angle to minimize the risk of tip necrosis. When planning a trifurcation incision, acute angles (< 45 degrees) should always be avoided. Most importantly, the point of trifurcation must be placed over the SCM when possible. This is the most likely area for wound complications, so placing the trifurcation point over a critical structure, such as the carotid or the brachial plexus, can lead to significant morbidity in this event. If there is significant risk of carotid exposure (such as history of radiation or radical neck dissection), consider an elective interposition of myofascial pec- toralis flap to protect these critical structures. This posterior limb can usually be placed within a dominant skin crease and may be extended to the posterior midline (or beyond) when performing a posterolateral neck dissection, which also encompasses the suboccipital and postauricular lymphatic groups.
Taking these points into consideration, the posterior elevation of skin flaps proceeds until the anterior border of the trapezius muscle is widely exposed (Fig. 7.7).
7.2.4 Preservation of the Marginal Mandibular Branch of the Facial Nerve
A thorough understanding of the anatomy of the facial nerve and its relationships with neck structures is critical to preserve the function of its marginal mandibular branch (marginal nerve) and consequently perioral musculature. The marginal nerve is the fourth most inferior branch of the facial nerve, and after it has originated from its lower division, it exits the anteroinferior portion of the parotid near the angle of the mandible and remains deep to the investing cervical fascia. Near the mandibular midbody, the nerve swings upward and perforates the DCF near the mandibular border to continue within the fibroareolar tissue between the deep fascia and platysma. It continues anteriorly at this plane to innervate the depressor labii inferioris, depressor anguli oris, and mentalis muscles (Fig. 7.8). The effects of each of these muscles are as follows:
• Depressor labii inferioris draws the lower lip downward (depresses) and laterally (irony).
• Depressor anguli oris depresses the oral commissure (frown).
• Mentalis raises and protrudes lower lip and wrinkles skin of chin (pout).
Fig. 7.7 Completed neck elevation over the posterior neck triangle. DG, digastric muscle; GAN, greater auricular nerve; SCM, sternocleidomastoid muscle; TRP, trapezius muscle; XII, hypoglossal nerve.
Fig.7.8 Anatomical disposition of the muscles innervated by the marginal nerve.
On the other hand, the cervical branch of the facial nerve further divides into an upper and a lower branch (Fig. 7.9); these will innervate the platysma muscle and may have an effect on preserving lip symmetry. Distally, the marginal nerve can anastomose with other branches of the facial nerve (most commonly buccal) to create a plexus that will innervate the perioral musculature. The location of the nerve in relationship to the lower border of the mandible is variable; furthermore, this relationship may change depending on the segment of the nerve analyzed (anterior vs. posterior to the facial artery), as shown in Table 7.3. This anatomical variability was also demonstrated by Al-Qahtani et al,7 who showed that the nerve has a sinuous pattern in three-fourths of the cases, and in 15% it loops posteriorly beyond its point of origin (Fig. 7.10). The nerve almost invariably (90%) courses as a single branch as it exits the parotid and throughout its course. However, distally, as it approaches the effector musculature, it expresses a branching pattern in more than 80% of the cases.8
Fig. 7.9 Illustration showing the anatomical relationship of the marginal and cervical branches of the facial nerve.
Table 7.3 Summary of studies reviewing the anatomical relationship of the marginal nerve with the lower border of the mandible
|
Study |
Subjects |
Reference to facial artery |
Reference to lower border mandible |
|
|
Above |
Below |
|||
|
Dingman and Grabb 1962 |
Cadaver |
Anterior to |
100% |
0 |
|
Posterior to |
81% |
19% |
||
|
Wang et al 1991 |
Cadaver |
Anterior to |
90% |
10% |
|
Posterior to |
67% |
33% |
||
|
Savary et al 1997 |
Cadaver |
Anterior to |
27% |
27% |
|
Nelson and Gingrass 1979 |
Cadaver |
100% |
||
|
Woltmann et al 2006 |
Cadaver |
57% |
43% |
|
|
Ziarah and Atkinson 1981 |
Cadaver |
47% |
53% |
|
|
Nason et al 2007 |
Patient |
64% |
||
|
Baker and Conley 1979 |
Patient |
Almost 100% |
||
|
Source: Adapted from Al-Qahtani et al.7 |
||||
From the surgical standpoint, there are two ways to spare the nerve function:
• The Hayes Martin maneuver, which entails the ligation of the facial vein two fingerbreadths below the lower border of the mandible, and subsequent cephalad retraction of the superior stump (Fig. 7.11). Since the anatomy is constant in the sense that the marginal nerve is always superficial to the facial vessels at the mandibular edge, retracting the stump assures that the nerve will be contained within these fasciae. This is a time-tested approach that works well for most cases, but it has some limitations such as in cases where there is direct disease extension to the submental triangle, or significant nodal disease level Ib or in facial lymph nodes.
• Exploration of the marginal nerve. In this approach, the fascia overlying the submandibular gland is incised horizontally, about 2 cm below the midpoint of the mandibular body, which closely correlates with the location of the facial artery notch. Meticulous subfascial dissection is performed in a cau- dal-to-cephalad direction while maintaining a bloodless surgical field and minimizing the use of electrocautery. The facial vessels—and more specifically the facial artery—may be used as landmarks to identify the nerve, which will always be in a plane immediately superficial to the vessels and appear as a structure parallel to the mandible (Fig. 7.12). Once the nerve is identified, antegrade and retrograde dissections are performed until it is released from underlying attachments, and it can safely be reflected cephalad. Posteriorly, this dissection may course through the tail of the parotid gland, which in this case is reflected inferiorly and kept in continuity with the contents of level II. The level of the dissection must be continued until the posterosuperior boundaries of level IB (the lower border of the mandible and the stylohyoid muscles) are exposed. This approach is particularly useful if the anatomy is distorted or if there are facial lymphadenopathies.
Fig. 7.10 Anatomical variations of the course of the marginal nerve and their relative frequency.
7.2.5 LevelIa
This is usually the first level to be addressed, as it helps establish early anatomical points of reference and has a low potential for complications. In cases where a unilateral neck incision is performed, it is important to elevate skin flaps contralaterally (usually 2-3 cm) to expose the entire submental triangle. The fascia overlying the anterior belly of the digastric muscle is incised bilaterally in an anterior-to-posterior fashion with the Bo- vie electrocautery. If anterior jugular veins are identified over the boundaries of this level, it is safer to ligate them or control them with the harmonic scalpel, as the intraoperative combination of head elevation and relative hypotension may provide a false sense of hemostasis. Close to the anterior insertion of the muscle, medial branches of the submental artery may have to be controlled. Once the lateral boundaries of the dissection have been established, the anterior bellies of the muscles are reflected laterally, and the fibrofatty contents of level Ia are dissected off the mylohyoid muscle, in an anterior-to-posteri- or fashion. This proceeds until the body of the hyoid bone is encountered (Fig. 7.13). At this point, the specimen is transected at its base with the harmonic scalpel and sent for pathological analysis.
7.2.6 Level Ib
Once the marginal nerve has been addressed, attention is turned to defining the boundaries of the dissection. This triangular-shaped level defined by the anterior and posterior bellies of the digastric muscle, the lower border of the mandible, and the stylohyoid muscle. If the tail of the parotid gland extends over this compartment, it may be reflected superiorly, or transected and included in the specimen (after the continuity of the mandibular nerve has been established posteriorly). Depending on the drainage pattern of the superficial venous plexus, the retromandibular vein may need to be ligated to allow for adequate exposure. The submandibular glands may be ptotic, and extend below the boundaries of the digastric muscle, especially in elderly patients. In these cases, blunt dissection under hemo-stat exposure in the avascular plane immediately superficial to the muscle will help establish the boundaries while minimizing bleeding. This maneuver may be performed following the muscle in an anterior-to-posterior fashion or vice versa, all while the submandibular gland is retracted upward. The facial vein (and sometimes its branches) will course superficial to the gland, and must be ligated at this point (Fig. 7.14).
Once the boundaries of the level are exposed, the next step is to ligate the facial vein as it emerges superiorly to the posterior belly of the digastric. While this step can be performed later in the dissection, most of the structures in this level receive their blood supply from this vessel, so ligating it earlier helps minimize bleeding. To achieve this, the submandibular gland is grasped and reflected anterosuperiorly, the posterior belly of the digastric is reflected inferiorly, and a Kittner blunt dissector is used to gently explore the space between these two structures.
Fig. 7.11 Hayes Martin’s maneuver for preservation of the marginal nerve. (a) Ligation of the facial vein 2 cm below the mandibular border (* denotes transected facial vein). (b) Superior retraction of the stump over the marginal nerve. Marg, marginal mandibular branch of the facial nerve.
The facial artery, which will appear coursing superiorly in a plane perpendicular to the muscle, may be then be clipped or ligated at this level (Fig. 7.15).
Then, attention is turned to the anterior aspect of the dissection. The electrocautery is used to skeletonize the anterior belly of the digastric muscle, and the lower border of the mandible, carefully avoiding injuring the periosteum. Anteriorly, toward the angle created by the junction of these structures, the submental vessels appear in close relationship to the mandible, where they should be ligated. Then the anterior belly of the digastric is reflected inferiorly, and the fibrofatty contents of the space are dissected off the mylohyoid muscle in an anterior-to-posterior fashion with the electrocautery (Fig. 7.16). This maneuver must be performed in a slow, continuous fashion, always maintaining a plane of dissection perpendicular to the mandible, until the free (posterior) edge of the mylohyoid is encountered. There are some technical points to be noted about this part of the procedure:
• This is not an avascular plane, and vessels traversing the mylohyoid muscle in a deep to superficial plane will have to be controlled (ideally with clips or bipolar), as slow bleeding from these vessels may lead to postoperative hematoma.
• A dehiscence of the mylohyoid muscle (or mylohyoid boutonniere) has been reported in 36 to 41% of cadaver dissections,9.10 and as high as 77% of the population on imaging studies (Fig. 7.17).11 The difference is explained by the high sensibility of current imaging, which may detect clinically inapparent presentations. These cases are notorious for the protrusion of sublingual salivary tissue or fat—or both—into the submandibular space, putting these structures at risk during the dissection. While these anatomical variations may be identified in preoperative imaging, the surgeon must always carry a high index of suspicion during this portion of the dissection, as this condition may be quite confusing for the neophytes.
• Zealous resection of all the fibrofatty contents must be ensured. Upon completion of this portion, the digastric muscle, mylohyoid muscle, and the mandible should be devoid of any apparent soft tissue.
At this point, the detached components of the anterior level Ib and the submandibular gland are grasped together. A Green loop retractor is gently placed under the mylohyoid muscle and used to reflect the muscle anteriorly. The gland is then reflected superiorly to expose the hypoglossal nerve, which will be found deep and slightly superior to the digastric tendon (Fig. 7.18a). The gland is then reflected inferiorly to expose the lingual nerve and the submandibular ganglion, which lies in close proximity to the gland (Fig. 7.18b). The submandibular gland duct is located parallel to the lingual nerve, in a position immediately inferior to it. The duct is thin walled and surrounded by salivary gland parenchyma, so under normal circumstances it may be difficult to identify, but the opposite is true if it is obstructed distally (such as floor of mouth tumors). In these cases, the duct is widely dilated and filled with mucopurulent content, markedly facilitating its identification.
Fig.7.12 Identification of the marginal branch by direct exploration. (a) Horizontal incision of the fascia over the right submandibular gland. (b) Superior elevation in the subfascial plane to expose the marginal nerve (arrow); * denote level Ib lymph nodes. SCM, sternocleidomastoid muscle; SMG, submandibular gland.
Fig.7.13 Dissection of level Ia. The specimen (*) has been dissected off the anterior bellies of the digastric muscles, and the mylohyoid muscle. DG, digastric muscle.
Fig. 7.14 Dissection of level Ib: facial vein (*) and submandibular gland. DG, digastric muscle; SAN, spinal accessory nerve; SCM, sternocleidomastoid muscle; SMG, submandibular gland.
Once all of these structures are identified, any soft tissue connections to the specimen or the submandibular gland are transected, leaving the gland attached anteriorly only by the lingual nerve and submandibular duct. The duct and submandibular ganglion are then clamped together, and the specimen is transected over the clamp and sent to pathological analysis. During this maneuver, especial care must be taken to avoid grasping the trunk of the lingual nerve with the clamp, and it is recommended that cold instrumentation be used to release the specimen in order to avoid electrocautery-related neuropraxia.
Alternatively, the specimen may be kept in continuity with the contents of the lateral neck by preserving the fascia overlying the posterior belly of the digastric muscle. This approach is technically more challenging and has questionable oncological benefits, so it is not routinely recommended.
7.2.7 Level II
The jugular lymph nodes (levels II-IV) are part of a continuum of lymphoid tissue that in the context of a modified radical neck dissection is routinely addressed as a single specimen. The boundaries between these levels are not anatomical, but arbitrarily established to help conceptualize the degree of nodal extension in the neck. In the following section, the critical aspects of the dissection of levels II to IV will be addressed separately; however, it is important to highlight that in reality there is significant overlap between these surgical steps.
To expose the jugular lymph nodes, the first step is to widely expose the SCM from its sternoclavicular insertion to the mastoid. In this regard, if the skin flap elevation was insufficient, it must be expanded accordingly using the same principles previously described. A thorough understanding of the fascial compartments of the neck is particularly important for this portion of the procedure, and this topic is addressed in detail in Chapter 3. The SLDCF (or investing layer) wraps around the SCM covering its internal and external aspects (Chapter 3; Fig. 3.7). The fascia is incised along the anterior border of the SCM from the mastoid to its sternal insertion. The muscle is then reflected laterally, and the dissection proceeds on its internal aspect, in a superior-to-inferior fashion, while aiming to preserve its fascial envelope (Fig. 7.19). During this process, the segmental blood supply to the muscle, which originates from the occipital, superior thyroid, and transverse cervical arteries,12 is controlled with the harmonic scalpel as it enters the muscle. This maneuver proceeds continuously, aiming toward the posterior aspect of the muscle as it is gently released and reflected.
Fig.7.15 Dissection of level Ib: ligation of the facial artery exposed by the instrument. DG, digastric muscle; EJV, external jugular vein; SCM, sternocleidomastoid muscle; SMG, submandibular gland.
Fig.7.16 Dissection of level Ib. As the anterior belly of the digastric muscle is retracted anteriorly, the specimen (*) which contains the submandibular gland and fibrofatty contents of level Ib is dissected off the mylohyoid muscle. DG, digastric muscle; Marg, marginal mandibular branch of the facial nerve; MH, mylohyoid muscle; SCM, sternocleidomastoid muscle.
7.2.8 External Jugular Nodes
The external jugular lymph nodes are located on the lateral aspect of the SCM, along the course of this vessel, and deep to the investing fascia of the muscle. Routinely, this group is not electively included when the procedure is indicated for aerodigestive tract malignancies, but it should be addressed in other circumstances, such as in the presence of positive lymph nodes or for cutaneous malignancies. To address these, the fascia overlying the SCM is incised along the posterior border of the muscle, transecting the greater auricular and related sensory branches. The fascia (containing this nodal group) is then reflected anteriorly, and detached from the lateral surface of the SCM in a posterior-to-anterior fashion. The external jugular vein is transected on its superior aspect—as it merges with the retromandibular vein—and inferiorly as it leaves the confines of the SCM muscle. As soon as the dissection reaches the anterior edge of the SCM, the specimen may be amputated and sent for pathologic analysis, or maintained in continuity with the contents of levels II to IV.
Fig. 7.17 Diagram of a mylohyoid muscle dehiscence.
7.2.9 Identification of the Spinal Accessory Nerve
Roughly midpoint through the dissection on the internal aspect of the SCM, and on the upper third of the muscle (level II), the SAN should be actively searched for. The nerve is usually surrounded by blood vessels, and care must be taken to avoid mistaking it for a vascular structure. The main trunk of the nerve (or the branch to the SCM) consistently enters the muscle on its internal aspect at this level, but other aspects of the anatomical relationship between the SAN and the SCM are significantly more variable. In an anatomical study aimed at documenting the anatomy of the SCM branch, Shiozaki at al13 described three patterns for innervation of this muscle, which are presented in Table 7.4. In all the assessed specimens, either the trunk of the nerve or a major motor branch was confirmed to enter the SCM at its anticipated location, thus confirming the notion that the proximal portion of the nerve has a relatively constant anatomy.
On the other hand, distal arborization, specifically as it relates to the trapezius branch and cervical contributions, varies greatly. Recent studies have relied on electrophysiological analysis to provide further insight into these variations. Gavid et al14 used this technique to assess the contributions of cervical nerves to the motor innervation of the trapezius muscle in cadavers. They found that while anatomical communications between the SAN cervical nerves were common (78% for C2, 48% for C3, and 52% for C4), in only 32% of the cases did they elicit a motor event in the trapezius. These findings suggest that the majority of cervical anastomoses could be sensory in nature. Similarly, Lanisnik recently described a functional classification of the anatomical variations of the trapezius branch by using electromyography in patients undergoing neck dissections15 (Table 7.5). This study highlights the complexity of the neural connections at this level, and helps explain why patients in whom the main trunk of the nerve was spared may present with shoulder impingement syndrome in the postoperative period. There is also anatomical variability of the nerve beyond its major motor branches to the SCM and trapezius muscles. Tubbs et al16 describe that in 1.8% of the cases the nerve is duplicated (intracranially or extracrani- ally) and that the nerve is communicated with—or gives origin to—the lesser occipital nerve in 5.4% of the cases. While these findings have little implication in terms of surgical technique, they should serve as a reminder of the variability and complexity of the SAN anatomy.
Fig. 7.18 (a) Superior retraction of the specimen to expose the hypoglossal nerve (*). (b) Inferior retraction of the specimen to expose the lingual nerve. DG, digastric muscle; LN, lingual nerve; MH, mylohyoid muscle.
Fig. 7.19 Incision of the fascia over the anterior border of the sternocleidomastoid muscle, and initial retraction of the muscle. DG, digastric muscle.
Table 7.4 Patterns for spinal accessory nerve (SAN) innervation of the sternocleidomastoid muscle (SCM)13
|
Type |
Description |
Frequency (%) |
|
A |
A branch of the SAN innervates the SCM, but the main trunk of the nerve courses posteriorly along its inner surface without penetrating the muscle. |
45.9 |
|
B |
The main trunk of the SAN penetrates SCM and then reappears posteriorly as the branch to the trapezius muscle. |
50.8 |
|
C |
The main trunk of the SAN penetrates the SCM and emerges on its lateral surface as the branch to the trapezius muscle. |
3.3 |
Table 7.5 Anatomical patterns of spinal accessory nerve (SAN) for innervation of the trapezius muscle, description and frequency according to Lanisnik15
As illustrated by these studies, meticulous and conservative dissection of the nerve, and all its branches and anastomoses, is paramount to achieve the best functional results. From the technique standpoint, this may be achieved by focusing on the more constant part of the nerve anatomy (identifying it as it enters the SCM) and subsequently utilizing meticulous retrograde dissection to expand on these findings. Special care must be taken to identify and spare the cervical contributions. These are commonly located at the posterior edge of the SCM, and consistently reach the trunk of the nerve from its caudal aspect. It is strongly recommended to use fine instrumentation, and limit electrocautery use to the bipolar, while actively dissecting this neural plexus.
7.2.10 Defining the Anatomy of the Superior Boundary of the Dissection
At this point, the posterior belly of the digastric should be completely exposed and dissected posteriorly until its junction with the SCM is widely exposed. As described earlier, the main trunk of the SAN should have been identified and isolated on the internal aspect of the SCM muscle. Then, the posterior belly is reflected superiorly and the SCM laterally to create a triangular working space. Weitlaner autostatic retractors may be used to facilitate exposure, but care must be taken to avoid placing them close to neurovascular structures. The trunk of the SAN is dissected cephalad aiming for the posterior belly of the digastric. At this point, establishing the anatomical relationship between the nerve and the superior aspect of the IJV becomes the main objective. In this regard, there are three possible relationships between the structures: the nerve may be lateral to the IJV, medial to the IJV, or go through it (also known as IJV duplication). As presented in Table 7.6, the relative frequencies of these anatomical dispositions vary widely in the medical literature, yet from this author’s observations, at this level the nerve is almost always lateral to the vein. In addition to this relationship, the surgeon must be aware of two anatomical considerations that warrant meticulous surgical technique:
• Commonly, the IJV will have small branches that course anteriorly or posteriorly, at or below the plane of the posterior belly of the digastric muscle. These may be a source of bleeding that is difficult to control given the limited exposure.
• The occipital artery can be consistently found in this region, as it courses posterosuperiorly in a plane superficial to the IJV and the SAN. In terms of the cephalocaudal location, in most patients the vessel has a course that is parallel and immediately deep to the posterior belly of the digastric muscle, but it may also be caudal to the muscle, and well within the boundaries of level II. When visualized, the occipital artery commonly interjects with the trunk of the SAN at a 45- to 90-degree angle. If the vessel is within the confines of level II, it may be ligated without apparent deficit (Fig. 7.20).
Table 7.6 Anatomical relationship between the spinal accessory nerve (SAN) and the internal jugular vein (IJV)
Source: Adapted from Taylor et al.25
Note: Illustrations depict the posterior belly of the digastric muscle, the superior aspect of the internal jugular vein, and the main trunk of the SAN.
7.2.11 Sublevel Ilb
In the recent medical literature, there is growing evidence supporting conservative management of this level in multiple clinical scenarios, unless there is Frank’s disease in level IIa.17,18 There is a well-established rationale for this, as dissection of this level has been associated with a significant increase in shoulder dysfunction on multiple accounts.19 There is also an anatomical component adding to the variability, as in some patients the trunk of the SAN enters the SCM muscle very close to its mastoid insertion, leaving little—if any—lymphoid tissue in this level.
From the standpoint of technique, this sublevel may be resected as a separate specimen, or in continuity with the rest of the lateral neck, which is this author’s preference. Proper exposure is paramount to achieve an oncologically sound resection of the contents of the submuscular triangle. An autostatic retractor is used to separate the posterior belly of the digastric and the upper aspect of the SCM, and a small Richardson retractor placed in the junction of these two muscles. Then, the trunk of the SAN (which at this point has been dissected) is gently retracted anteroinferiorly with a nerve hook. This four-point retraction technique provides the best possible exposure of this sublevel. Then, using the Bovie electrocautery, the specimen is first detached from the undersurface of the SCM (aiming at its posterior boundary) and from the posterior belly of the digastric muscle. This can be a swift maneuver as there are no cervical rootlets above the level of the SAN in this region. It is recommended that the assistant use an Andrews-Pynchon suction, as the liquefied fats of the specimen reduce the efficiency of the electrocautery. Once the posterior and superior boundaries of the resection are defined, the specimen is gently grasped and dissected off the floor of the neck musculature, which at this level is constituted by the splenius capitis and the levator scapula muscle (Fig. 7.21). This maneuver is performed in a posterior-to-anterior fashion until the level of the SAN and the lateral aspect of the IJV are reached. It is important to note that, at this level, the lateral aspect of the IJV should have been previously dissected and exposed prior to addressing level IIb. Otherwise, there is risk for a high vascular injury of the vein, which is notoriously difficult to control. The specimen is then translocated under the trunk of the SAN and kept in continuity with the contents of level IIa.
Fig. 7.20 Dissection of level II. The posterior belly of the digastric muscle is retracted, and the occipital artery (*) is seen coursing posterolaterally though level II. DG, digastric muscle; MH, mylohyoid muscle; SAN, spinal accessory nerve; SCM, sternocleidomastoid muscle.
Fig. 7.21 Dissection of submuscular recess (level IIb). As the spinal accessory nerve is retracted anteriorly, the specimen (*) is dissected off the digastric, SCM and floor of the neck musculature. DG, digastric muscle; LS, levator scapulae muscle; SAN, spinal accessory nerve; SCM, sternocleidomastoid muscle.
Fig. 7.22 Dissection of the cervical rootlets in level III. Note the branch to the trapezius muscle from the spinal accessory nerve (*). CR, transected cervical rootlets; SAN, spinal accessory nerve; SCM, sternocleidomastoid muscle.
It must be noted that the occipital artery may be visualized in this sublevel and be a source of intraoperative bleeding. If this is the case, it must be transected and partially included with the specimen.
7.2.12 Level III
The dissection proceeds along the internal aspect of the SCM muscle in a cephalad-to-caudal fashion. At this level, the main focus is to identify and dissect cervical rootlets, and most importantly, spare the contributions they may have to the trapezius branch of the SAN. It is recommended that the surgeon be very familiar with the variations in the neural anatomy in this region, as presented in Table 7.5. The specimen involving levels II and III (and subsequently IV) is grasped with Allis clamps and reflected medially by the assistant in an even fashion. Once the rootlets are visualized on the undersurface of the posterior edge of the SCM, they are dissected toward their point of emergence in the floor of the neck. There is a natural plane of dissection immediately superficial to each rootlet, so from this author’s perspective this is better achieved with the blunt dissection technique under hemostat exposure. As each rootlet is dissected, the specimen is sequentially released, opening the surgical field to proceed to the next (caudal) nerve (Fig. 7.22). From the anatomical standpoint, the plane of the rootlets marks the posterior boundary of levels III and IV, so there is no need to proceed deep to these structures at this stage. However, it must be noted that the fibrofatty tissue superficial to virtual plane that connects the rootlets should be included with the specimen. This is a common point of confusion, and a potential pitfall from the oncologic perspective, among other reasons, because there are no anatomical landmarks other than the rootlets. When two consecutive rootlets are exposed, a helpful maneuver is to dissect the most caudal one and open the fascia overlying it while reflecting the soft tissues located in between the rootlets, over the instrument. This assures an even plane of dissection while minimizing the risk of an incomplete removal of lymphatic tissues.
The rest of the dissection of level III involves detaching the specimen off the floor of the neck musculature, which is performed with level IV and will be discussed in the following section.
7.2.13 Level IV
This is an important level, as it carries significant risk to neurovascular structures and potential for significant complications. Thorough knowledge of the anatomy of the region is essential to reduce the risk of complications.
Normally, this level will be performed sequentially after level III, proceeding with the continuum, that is, the dissection of the lateral neck. At this point, the anterior fascia of the SCM has been opened, and the rootlets of level III identified and dissected. The next step is to provide ample exposure of this region, which is achieved by aggressive lateral retraction of the lower third of the SCM, and medial countertraction of the visceral compartment by the assistant. This maneuver exposes the omohyoid muscle, which serves not only as an intraoperative boundary between levels III and IV, but also as a landmark to identify the caudal aspect of the IJV, which lies immediately deep to its tendon. The muscle is transected at the level of its tendon, which allows for further exposure of the caudal jugular vein (Fig. 7.23). At this point, it is recommended to palpate and acknowledge the location of the clavicle, the inferior boundary for the dissection. Since the procedure is being performed on a deeper plane, it is easy to lose perspective and transect the specimen too high on the neck, or too low toward the mediastinum.
Once the stage has been set, the first step is to continue the dissection on the undersurface of the SCM, as carried along from level III. The surgeon must actively look for lower cervical rootlets in this area, which will have the same anatomical disposition as in levels above and should be addressed likewise. Once the most caudal rootlet has been dissected, the junction where it intersects the posterior edge of the SCM (as seen from its undersurface) becomes the pivotal point where the dissection turns medially to define the caudal boundary of level IV. This should roughly correlate with the level of the clavicle on surface anatomy.
At this stage, the specimen is still attached medially to the IJV, and to the floor of the neck, which at this level is constituted primarily by the anterior and middle scalene muscles. The transverse cervical vessels have a medial-to-lateral course in a plane immediately superficial to the prevertebral fascia. The phrenic nerve courses in an oblique plane over the surface of the anterior scalene, protected by this fascia. It is good practice to keep these constant anatomical relationships in mind, because if at any time the fibers of the anterior scalene become visible, the plane of dissection is too deep and it must be corrected immediately.
The surgeon must also be familiar with the lymphatic anatomy of the region, which is significantly more variable. At a rate of 1 to 2.5% of all modified radical neck dissections, the risk of postoperative chyle leak is low. This incidence, however, may be underreporting, as prospective studies have documented it as high as 8.3%.20 The most important vessel in this regard is the thoracic duct, which measures about 45 cm in length, but only 2 to 3 mm in diameter. It courses superiorly on the left side, through the mediastinum, to drain on the posterior aspect of the junction between the internal jugular and the subclavian veins (Fig. 7.24). However, there is significant variation of the course and termination of the duct, and it can drain higher (directly to the IJV) placing the patient at considerable risk for a chylous fistula.
Anatomically, on the right side there are three major lymphatic trunks (jugular, subclavian, and bronchomediastinal), which most commonly drain independently to the posterior aspect of the subclavian. However, in one-third of the cases, these trunks converge to form a larger vessel known as the right lymphatic duct, which has a short course (1-2 cm) to drain in the same location as the contralateral thoracic duct21 (Fig. 7.25). In the event of an injury to the right-sided duct, the patient presents with a lymphatic fistula, but no chyle, as this fluid will lack the enteric component. A common misconception is to attribute the risk of chyle leaks only to left-sided neck dissections. This is not true, as in 1 to 5% of the cases, the thoracic duct will drain on the right side, and there are also accounts ofbilateral thoracic ducts. For these reasons, it is recommended that the surgeon have the same careful approach as to the lower neck, regardless of the side of the dissection.
Traditionally, to establish the lower boundary for the dissection in level IV, a lateral-to-medial approach has been advocated. In this setting, the specimen is retracted medially, and the dissection proceeds medially from the posterior border of the SCM muscle (below the level of the lowest rootlet), over the prevertebral fascia and toward the IJV. While this is feasible and usually safe, it can be challenging, as the angle for dissection is not comfortable for the surgeon, and the plane transitions from deep to superficial (as the prominence of the anterior scalene muscle is encountered from the side). Also, the fascial planes are not as well defined laterally, close to the posterior border of the SCM muscle.
Fig. 7.23 Transection of the tendon of the omohyoid muscle (*) to expose level IV. CR, transected cervical rootlets; IJV, internal jugular vein; SCM, sternocleidomastoid muscle.
Fig. 7.24 Illustration of the anatomy of the thoracic duct, as it drains to the left jugulo- subclavian junction.
Fig. 7.25 Illustration of the variations in drainage patterns of the right neck lymphatics. a = jugular trunk, b = subclavian trunk, c = bronchomediastinal trunk, d = right lymphatic trunk, e = gland of internal mammary chain, f = gland of deep cervical chain.
An alternative maneuver to define the lower boundary of level IV is a medial-to-lateral approach; based on this author’s experience, this is easier to execute, more consistent, and proceeds as follows: when the lowest rootlet has been dissected on the medial aspect of the SCM, this point is marked with an instrument. Then the IJV is exposed at the level of the clavicle, and the fascia on its lateral aspect opened vertically over 3 to 4 cm, thus creating a “pocket” immediately lateral to the vein. Then, as the IJV is reflected medially and the rest of the specimen laterally, this pocket is expanded using a Kittner dissector for atraumatic blunt dissection. To establish a reference point, the surgeon must palpate the convexity of the anterior scalene muscle, and the dissection is oriented toward this structure. This is usually a relatively avascular plane, but if any bleeding is encountered it must be controlled immediately. Once the plane of the anterior scalene muscle is reached, the specimen is reflected upward (i.e., lifted off the neck) and blunt dissection with a Kittner dissector ensues over the anterior aspect in a medial-to-lateral fashion. At this point, the phrenic nerve will usually become apparent in the anterior surface of the muscle, behind a layer of pre- vertebral fascia. The main trunk of the transverse cervical vessels can usually be seen heading laterally over the plane of the nerve; these vessels may be dissected laterally and spared (Fig. 7.26).
The dissection continues laterally in the same plane (over the scalene muscles) directed toward the point where the last rootlet intersects with the SCM, all while continuously gently lifting the specimen off the neck. When this point is reached, there is effectively a tunnel separating critical structures (deep), from the fibro- fatty contents of level IV (superficial). At this stage, the caudal attachments of the specimen are transected and ligated in multiple sections, under direct visualization of the phrenic nerve. The thoracic duct—or major lymphatics vessels—can usually be visualized with this maneuver, located in a plane immediately lateral and posterior to the IJV (Fig. 7.27). Most commonly, they can be spared, but if there is nodal disease in the area—or if located within the boundaries of level IV—they should be ligated.
Fig. 7.26 Contralateral view of the right level IV dissection. The SCM and IJV are retracted. A medial-to-lateral approach has been used to expose the transverse cervical artery (**) and the phrenic nerve (*) over the anterior scalene muscle. IJV, internal jugular vein; SCM, sternocleidomastoid muscle.
At this point, the specimen encompassing levels II to IV has been released superiorly, laterally, and inferiorly, and remains partially attached to the floor of the neck, and medially to the IJV. The next step is to detach these levels off the floor of the neck musculature. Any incompletely dissected rootlets are addressed, further releasing the specimen medially. As it relates to the floor of the neck, the prevertebral facial planes are more clearly defined on its lower third than in the superior two-thirds, among other reasons because of the course of the cervical rootlets. As such, one of the most significant risks during this stage is an injury to the phrenic nerve close to its origin, or to its contributions from C3-C5. In this regard, there are a couple of predisposing factors that should be pointed out, one being excessive traction of the specimen, which distorts the surgical planes and elevates the plane of the prevertebral fascia, and the other being the convexity of the anterior scalene muscle. It is important to conceptualize that, as the dissection proceeds medially and approaches the IJV, it should transition to a more superficial plane (and merge to the lateral aspect of the vein, which is roughly 2 cm superficial to the prevertebral fascia). Failing to do so (i.e., following the prevertebral fascia medially) leads to dissection underneath the IJV, posing significant risk to the carotid artery, vagus nerve, and cervical sympathetic chain. A helpful maneuver to properly address this surgical plane transition is to dissect with a hemostat on the lateral aspect of the IJV in a caudal-to-cephalad fashion, and reflect the specimen medially over the instrument (Fig. 7.28). This all but guarantees the indemnity of the deep fascial planes and the neural structures within it. Roughly at the midpoint of the IJV, the surgeon will encounter the cervical contributions from C2-C3 forming the inferior root of the ansa cervicalis. This nerve can be identified coursing anteromedially from floor of the neck and looping over the vein, where it can be safely transected.
Fig. 7.27 Thoracic duct (*) identified during the dissection of left level IV. IJV, internal jugular vein; SCM, sternocleidomastoid muscle.
Fig. 7.28 Detaching the specimen off the prevertebral plane while dissecting on the lateral surface of the internal jugular vein; ansa cervicalis (*) can be seen crossing over the IJV. DG, digastric muscle; IJV, internal jugular vein; SCM, sternocleidomastoid muscle.
A tortuous internal carotid artery is an innocuous anatomical variation that can pose a risk in this part of the procedure. While releasing the specimen superiorly, close to the posterior belly of the digastric muscle, this vessel can appear like a level II lymphadenopathy adjacent to the floor of the neck; the surgeon must have a high index of suspicion to avoid a major vascular injury in these cases.
Once the specimen has been released from the floor, the IJV should appear widely exposed from the clavicle to the digastric. At this stage, the specimen is reflected superomedially over the vein, and the vessel is skeletonized in the subadventitial plane with a scalpel in a lateral-to-medial fashion. Appropriate tension is essential to safely perform this maneuver. It is recommended that the specimen is grasped with four Allis clamps and retracted in an even fashion, while the surgeon uses a sponge on his or her nondominant hand to provide even countertraction to the vessel (Fig. 7.29). There are few branches on the lateral aspect of the vein, but they appear as the dissection proceeds medially and all these branches must be identified (prior to transection) and sequentially ligated. The common facial vein is usually the largest branch, and it may be ligated or dissected medially to minimize the functional impact of the procedure. Small injuries to the vein can usually be addressed with a clip (if there is a stump present) or by using two clips in a “V” disposition over the lateral wall of the vessel (if there is no stump). Larger injuries to the vein should be repaired with a Satinsky clamp with proper vascular technique. The dissection proceeds until the IJV is freed on its medial aspect, leaving the specimen attached to the carotid artery and strap muscles.
The next step is to identify the hypoglossal nerve on the carotid triangle. The nerve is deep to the tendon of the digastric muscle, and courses over the internal and external carotid arteries. To expose it, the posterior belly of the digastric muscle is reflected superiorly, and blunt dissection is performed a couple of centimeters caudal to the muscle, in a plane parallel to the hyoid bone; the nerve should become apparent as it loops anteriorly heading toward the submandibular triangle. The hypoglossal venous plexus (or ranine veins) consistently crosses over the nerve at this level. These vessels (which drain to the common facial vein) can be quite large and may represent a source for postoperative bleeding. Blunt dissection is performed over the hypoglossal nerve to expose and either ligate or transect these veins with the harmonic scalpel.
At this level, the superior branch of the ansa cervicalis (C1) should be visualized as it detaches from the hypoglossal nerve with a caudal direction over the carotid, heading to the strap muscles. When possible, this nerve should be preserved, as it may provide a useful landmark for the medial dissection of the specimen (Fig. 7.30). When the anatomy of the upper neck is challenging (such as reoperative cases, or severe actinic damage), the ansa cervicalis can be retrogradely dissected to safely identify the hypoglossal nerve.
The final step in the dissection of levels II to IV is the medial release of the specimen from its boundary, defined as the lateral border of the sternohyoid muscle. On the superior part of the neck, the omohyoid muscle (which has been transected) may serve as a surrogate structure to establish this plane, while inferiorly the sternohyoid must be exposed. The lateral aspect of the strap muscles is skeletonized with the Bovie electrocautery, and the fascia lateral to it grasped with Allis clamps. Retrograde dissection (in a medial-to-lateral fashion) ensues proceeding toward rest of the specimen that is over the carotid artery (Fig. 7.31). During the anterior approach to the carotid triangle, prominent perforating venous branches that connect the superficial and deep venous systems (from the superior thyroid to the anterior jugular) will be encountered. These must be ligated or transected with the harmonic scalpel, and care must be taken not to injure the superior thyroid artery during this process. Similarly, it is good practice to confirm the location of the hypoglossal nerve to avoid a distal injury. Finally, under direct visualization of all the critical structures, the specimen is detached from the carotid artery with the harmonic scalpel, divided into levels, and sent for pathological analysis.
7.2.14 Level V
As previously described, an accessory limb may be required to fully expose the boundaries of this level. The skin flaps must be elevated over the trapezius muscle (which should have its anterior border completely exposed) and inferiorly over the clavicle. Given the low rate of nodal involvement in this level, in contemporary oncological practice this level is commonly spared, unless Frank’s disease is present or there are specific indications such as a cutaneous or a nasopharyngeal cancer.
Fig. 7.29 Sharp dissection to release the contents of levels II to IV from the internal jugular vein.
Fig. 7.30 (a) Illustration of the cervical contributions to the ansa cervicalis. (b) Intraoperative image of a neck dissection where the entire loop of the ansa was dissected. The inferior root (C2-C3) and the superior root (C1) can be seen looping over the internal jugular vein. The hypoglossal nerve is also visualized. IJV, internal jugular vein; SAN, spinal accessory nerve; SCM, sternocleidomastoid muscle; XII, hypoglossal nerve.
Fig. 7.31 Dissection of the lateral border of the strap muscles, and release of the specimen over the carotid artery. CCA, carotid artery; DG, digastric muscle; IJV, internal jugular vein; SCM, sternocleidmastoid muscle; XII, hypoglossal nerve.
Fig. 7.32 Erb’s point (*) being used as a reference to identify the spinal accessory nerve in the posterior triangle of the neck. DG, digastric muscle; EJV, external jugular vein; SAN, spinal accessory nerve; SCM, sternocleidomastoid muscle; TRP, trapezius muscle.
The most important structure to preserve in this level is the trapezius branch of the SAN, which will emerge from the posterior border of the SCM and head posteroinferiorly, entering the trapezius muscle at the junction between its inferior third and its superior two-thirds. Another consideration is that the nerve enters the muscle from its undersurface, so during the dissection it will be perceived as “diving” under the muscle. This relationship is not consistently documented in the literature, and can be a source of confusion for neophyte practitioners. Because of its superficial location, and lack of clear anatomical boundaries, the nerve is at imminent risk during its entire course through the posterior triangle. As discussed earlier in this chapter, this is especially true when raising the skin flaps.
On their anatomical study, Shiozaki et al13 describe five different branching patterns of the trapezius branch as it enters the anterior border of the muscle in the posterior neck triangle. In type 0 (3.8%), the main trunk of the CN XI did not exhibit any branching; in type 1 (50%), the main trunk produced one branch; in type 2 (26.9%), two branches were observed separating from the main trunk; in type 3 (11.5%), the main trunk produced three branches; and, finally, in type 4 (7.9%), the main trunk produced four branches.
There are several strategies to identify the nerve in the posterior triangle, and the surgeon must be familiar will all of them: • Using Erb’s point. The nerve can be identified on the posterior border of the SCM muscle, 1 to 2 cm above Erb’s point—or nerve point—defined as the location where the four superficial branches of the cervical plexus (greater auricular, lesser occipital, transverse cervical, and supraclavicular) emerge from behind the muscle (Chapter 3; Fig. 7.16). Once this point has been localized, the SCM is grasped and reflected anteriorly over a short segment, and the fascia along its posterior border is incised vertically and explored with atraumatic technique. The nerve will appear as a structure forming an acute angle with the SCM that will be located in a plane slightly deeper than the cervical nerves (Fig. 7.32).
• Dissection from an anterior approach. If the trapezius branch of the SAN is visualized during the dissection of the jugular chain, it can be further dissected through the same approach as it enters level V. Alternatively, the position of the nerve can be marked with an instrument to use as a reference point during the exploration of the posterior triangle.
• The nerve can also be identified as it reaches the trapezius muscle. The fascia is opened in the posterior triangle, and atraumatic dissection proceeds over the anterior aspect of the trapezius, focusing on the junction between its lower third and its superior two-thirds. The limitation of this technique is that the nerve commonly expresses a branching pattern, making retrograde dissection technically more challenging and riskier from the perspective of branch injury.
Regardless of the technique chosen, the next step is to completely dissect the nerve, and all of its branches, through its entire course in level V. This is better achieved by a combination of sharp instrumentation and bipolar electrocautery, which prevents unexpected nerve stimulation (Fig. 7.33).
The next step is dissection of the sublevel Va. The posterior border of the SCM (above the nerve) and the anterior border of the trapezius are skeletonized with the Bovie electrocautery. During this process, the lesser occipital nerve, which will originate from Erb’s point and will have a posterosuperior orientation, will have to be transected. The specimen is detached from the floor of the neck musculature in a cephalad-to-caudal fashion, carefully preserving the fascia over these muscles. This is an important technical point, as the nerve (or nerves) to the levator scapulae originate from C4-C5 and travel on the surface of the muscle, protected only by its fascial layer. Any injury to the nerve will result in a functional deficit characterized by inability to raise the scapula and shoulder superomedially. As the specimen is detached, the muscles encountered will be the splenius capitis, levator scapula, and the posterior scalene, while the middle and anterior scalene muscles will be exposed during the dissection of level Vb. Once the specimen is released, it is translocated under the SAN and kept in continuity with the contents of level Vb.
Then we turn our attention to level Vb. The SAN and its branches are reflected cephalad, and the boundaries of this sublevel are defined. Anteriorly, the posterior border of the SCM (below the nerve) is skeletonized. At this stage, the surgeon will encounter the supraclavicular nerve with its medial, intermediate, and lateral branches, which will originate from Erb’s point and course inferolaterally in a superficial plane. These sensory rootlets must be sacrificed to address this sublevel, but when transecting them, it is important to leave a short stump at their point of origin to prevent injury to a cervical contribution of the phrenic nerve.
Inferiorly, the clavicle is exposed and the external jugular vein is transected at this level. Posteriorly, the omohyoid muscle will be identified and can be used as a surrogate for the inferior boundary of the resection. At this stage, the posterior border of the SCM muscle is reflected anteriorly, which should expose the previously dissected IJV, anterior scalene, and phrenic nerve. The brachial plexus is covered by a thick fascial layer, and upon palpation it feels like a thick, noncompressible cord. The location of the brachial plexus is established, usually by palpation first. Once this structure has been identified, blunt dissection from medial to lateral is performed on a plane immediately superficial to the prevertebral fascia, releasing the specimen inferiorly. Anatomically, the contents of the supraclavicular fossa are continuous with the axillary fat, so as the dissection proceeds laterally, an arbitrary transection point is defined using the clavicle as a point of reference. In other words, the surgeon must avoid “pulling up” fat from below the clavicular plane. The harmonic scalpel works well in this situation, as there will be blood vessels and lymphatics in the area. The specimen is then sent for pathologic analysis, leaving the posterior neck triangle devoid of any lymphatic tissues, and the dissected SAN anatomically intact (Fig. 7.34).
At this point, the neck is irrigated and hemostasis is confirmed under a Valsalva maneuver. Areas that should be directly explored are the undersurface of the SCM, branches of the transverse cervical vessels, hypoglossus venous plexus, and anterior jugular veins. The indemnity of the lymphatic system is confirmed by exploring level IV. While performing continuous abdominal compression,22 any lymphatic leak should be promptly repaired. Closed suction drains are placed, and the incisions are closed in two layers according to the surgeon’s preference.
7.3 Conclusion
The modified radical neck dissection is a comprehensive functional lymphadenectomy of the neck that only spares the groups in the central neck compartment. In this approach, the IJV, SAN, and SCM are spared, as well as all other significant neurovascular structures. This highly technical intervention demands for surgeons to master the anatomy of the neck, and to be familiarized with surgical strategies aimed at avoiding common intraoperative pitfalls. A systematic approach to this operation will help surgeons in training quickly to internalize the key elements necessary to perform this procedure safely and effectively.
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