Supraomohyoid Neck Dissection

Metastatic neck disease is the most important factor in the spread of head and neck squamous cell carcinoma (SCC) from primary sites. The most commonly involved primary sites are the mucosal areas of the upper aerodigestive tract, particularly the larynx, oropharynx, hypopharynx, and oral cavity. Lymph node (LN) metastasis reduces the survival rate of patients with SCC by half. The survival rate is less than 5% in patients who previously underwent surgery and have a recurrent metastasis in the neck. Therefore, control of the neck is one of the most important aspects in the successful management of these particular tumors.

Radical neck dissection is an operation that was created in 1906 to solve the problem of metastatic neck disease. This procedure is a well-designed operation that is relatively easy for the trained head and neck surgeon to learn and to perform. Classic radical neck dissection is still the criterion standard for surgical control of a neck metastasis.

In the last 3 decades, progressive advances have occurred in the understanding of cervical fascial planes, lymphatic drainage patterns, preoperative staging, and extracapsular spread. The necessity to maximize control and to minimize morbidity prompted modifications to the classic neck dissection. One such modification is the preservation of 1 or more nonlymphatic structures (eg, spinal accessory nerve, internal jugular vein [IJV], sternocleidomastoid [SCM] muscle).

Further observations indicated that the pattern of nodal disease depends on the primary site. Therefore, these findings led to another neck dissection modification, which is the selective preservation of 1 or several LN groups. The selected node groups represent the areas of high risk for early metastasis, depending on primary tumor location.

Selective neck dissection types

See the list below:

• Supraomohyoid or anterolateral - Levels I-III

• Lateral - Levels II-IV

• Posterolateral - Levels II-V, postauricular and suboccipital

• Anterior compartment - Level VI

In 1906, Crile was the first person to describe radical neck dissection, which encompasses the surgical removal of neck metastases contained between superficial and deep fascial layers of the neck. In the 1950s, Martin routinely used radical neck dissection for the management of neck metastasis. The main goal of this procedure was to remove, en bloc, all ipsilateral lymphatic structures from the mandible superiorly to the clavicle inferiorly and from the strap muscles to the anterior border of the trapezius.

The resection included the spinal accessory nerve, the IJV, the SCM muscle, and the submandibular gland. The carotid arteries, vagus nerve, hypoglossal nerves, brachial plexus, and phrenic nerve remained. This operation and its oncologic concept remain valid; however, the procedure has been modified to decrease morbidity while maintaining oncologic efficacy. In the 1960s, Suarez and Bocca independently described a more conservative operation that involved removing all the LNs while sparing the spinal accessory nerve, the SCM muscle, and the IJV. ^{[1, 2]}

Studies of the lymphatic system determined the likelihood of particular groups of LNs being involved based on the primary site. This ability to predict the location of metastatic disease was found valid and reliable in further studies. Based on that predictability, in the 1970s, surgeons from the MD Anderson Cancer Center designed a neck operation that spared some LN groups and sacrificed others. The main purpose of this neck operation was to create a more conservative and cosmetically oriented surgery without the decrease of oncologic control.

Multiple modifications to the radical neck operation necessitated the coining of neologisms to describe such changes; the terms for the same modification varied from author to author. These new varied and unclear terms created confusion among clinicians from different geographical areas and institutions. Therefore, standardization was necessary. In 1991, the American Academy of Otolaryngology-Head and Neck Surgery (AAOHNS) published an official report that standardized the terminology for different types of neck dissection. ^[3]

The report was updated and published in 2002 with only a few changes. These dealt with the application of various types of selective neck dissection procedures for oral cavity cancer, pharyngeal and laryngeal cancer, thyroid cancer, and cutaneous malignancies. ^[4] In addition, 2 new neck sublevels, Va and Vb, were added, for a total of 6 neck levels and 6 neck sublevels. (The 1991 version of the report listed only 4 neck sublevels.) With the exception of the 2 added neck sublevels, the terminology in the updated report is the same as that of the 1991 version. ^[5]

The Committee for Neck Dissection of the American Head and Neck Society presented a Classification in 2008 based on 4 types of neck dissection, as follows: ^[6]

• Radical neck dissection: It is considered "the standard neck dissection," including the resection of the lymphatic nodes in levels I, II, III, IV and V, as well as the sternocleidomastoid muscle, the spinal accessory nerve, and the internal jugular vein.

• Modified radical neck dissection: It is considered oncologically as radical as the radical neck dissection, removing the same lymphatic node levels but with preservation of at least 1 of the nonlymphatic structures. ^[7]

• Extended radical neck dissection: It is considered extended in the sense that additional lymphatic nodes as well nonlymphatic structures are removed.

• Selective neck dissection: It is a neck dissection in which one or more selected lymph node levels are preserved.

In 2010 the American Academy of Otolaryngology Head and Neck Surgery suggested a new terminology, more precise and easier to understand, in order to further standardize and make it easier to compare neck dissections and neck dissection results around the globe. An international effort was made to identify a rational classification format for neck dissections. The consensus was published in 2011.

This new classification system is based on 3 key terms from the new nomenclature. The first term is ND for "neck dissection." The second term is a Roman numeral indicating the lymphatic node level and sublevel removed during the dissection. The third term indicates the nonlymphatic structure included in the dissection. ^{[8, 9]}

Lymphatic metastasis is the most important mechanism in the spread of head and neck SCC. The risk of LN involvement by metastasis varies depending on the site of origin, size, histologic grade of the primary tumor, perineural invasion, perivascular invasion, and extracapsular spread. Management of the neck LNs is an integral part of treatment of head and neck cancer. Conversely, no single standardized treatment for cervical metastasis is available.

The indications for and type of neck dissection to be performed in the N+ neck and management of the N0 neck remain controversial. Management is based on personal experience and many retrospective studies.

Radical neck dissection was the first attempt to treat metastatic cervical lymphadenectomy adequately. The classic operation was modified several times to decrease morbidity without decreasing oncologic control. The 2 modifications commonly used today are the modified radical and the selective neck dissections.

Frequency

Incidence of metastatic disease for the upper aerodigestive tract varies from 1-85%, depending on the site, size, and differentiation of the tumor.

In the 1970s, several clinical studies revealed that nodal metastasis to the neck occurs in the following predictable patterns:

• Carcinomas of the oral cavity involve mostly the jugulodigastric and midjugular nodes.

• Lesions in the floor of the mouth or near the midline frequently cause metastasis bilaterally.

• Sites localized in the oral cavity, oral mucosa, oropharynx, hypopharynx, and supraglottis have a higher incidence of metastasis than areas such as the superior gingiva, hard palate, and glottis.

• Anterior portions of the oral cavity are associated with smaller risk of neck metastasis than the posterior portions.

• Young patients with oral carcinoma have a higher risk of nodal metastasis than older patients.

• The larger the primary tumor and/or the greater the depth of penetration, the higher the risk of neck involvement by metastasis.

• Perineural and perivascular invasion are associated with a high risk of nodal metastasis.

• Extracapsular spread carries a high probability for lymphatic spread.

• Poorly differentiated tumors are associated with a higher risk of neck metastasis.

Several retrospective reviews of specimens from radical neck dissections in the 1990s proved that SCCs of the oral cavity most commonly involve nodal levels I-III; level IV is involved 20% of the time, and level V is involved 4% of the time. Furthermore, SCCs at the hypopharyngeal level commonly metastasize to levels II-IV; metastasis to level I occurs 10% of the time, and metastasis to level V occurs 11% of the time. SCCs of the larynx are associated with similar areas and percentages, mostly to levels II-IV (level I, 8%; level V, 5%). Therefore, based on these patterns of nodal metastasis in SCCs, supraomohyoid neck dissection is an adequate node sampling procedure for cancer of the oral cavity.

Supraomohyoid neck dissection carries a recurrence rate of 5% in the N0 neck, 10% in the N+ neck with a single positive node, and 25% when multiple positive nodes or extracapsular spread is present. Supraomohyoid neck dissection is performed for the surgical control of early metastatic neck disease in a selected group of patients with SCCs of the oral cavity and skin cancer of the lip and face.

Metastasis occurs frequently in malignancies. The tumor grows at the primary site by malfunctions in cellular proliferation, differentiation, and death. Mutations due to chemical carcinogens, radiation, or viruses may cause normal cells to allow the activation of oncogenes; multiple genetic mutations, activation of proto-oncogenes, inactivation of tumor suppressor genes, or a combination cause alterations in growth control. Tumor cells move through the basement lamina of the epithelium and the stroma into the lymphatic and vascular channels (ie, cells move from carcinoma in situ to microinvasive tumor). This process is associated with the production of cytokines, enzymes, and growth factors that destroy the basement membrane, thus creating abnormal angiogenesis, which, in turn, triggers neovascularization and growth. The tumor spreads into the regional LNs from the lymphatic and vascular channels and sets up tumors in secondary sites.

Most candidates for supraomohyoid neck dissection present with early stage, (N0 or N1) metastatic neck disease due to SCC of the oral cavity. Usually, the patient is already aware of the primary lesion or it is found easily during physical examination of the upper aerodigestive tract. In 15% of patients, the neck mass is present without an obvious primary lesion.

Nodal classification

The most important prognostic factor in patients with SCC of the head and neck is the status of the neck nodes. The status of the cervical nodes constitutes the N portion of the tumor, node, metastases (TNM) classification by the American Joint Committee on Cancer (AJCC). The AJCC assigns N1-N3 ratings to different degrees of neck adenopathy, with subgroupings of a, b, and c for certain stages. The nodal classification is as follows:

• NX - Cervical neck nodes not assessable

• N0 - No cervical node metastasis

• N1 - Single ipsilateral node metastasis (≤3 cm diameter)

• N2a - Single ipsilateral node (>3 cm but ≤6 cm diameter)

• N2b - Multiple positive ipsilateral nodes (none >6 cm diameter)

• N2c - Bilateral or contralateral positive nodes (none >6 cm diameter)

• N3 - Massive adenopathy (>6 cm diameter)

Palpation

Accuracy of staging relates to the physician's ability to detect cervical adenopathy. Palpation is the technique used most to detect neck metastases. Although palpation is inexpensive and easy to perform, it is not totally reliable.

Sensitivity and specificity of neck examination by palpation range from 60-70%. A short obese neck and/or previous radiation or surgery makes the physical examination more difficult to perform. Negative palpation findings of the neck still indicate a risk of occult metastatic disease. This risk increases according to the site, size, and particular characteristics of the primary lesion.

Imaging

Imaging is an important part of clinical diagnosis and staging. However, imaging is indicated only if results are used in treatment management. Among these techniques are computed tomography (CT) scanning, magnetic resonance imaging (MRI), ultrasonography, and ultrasound-guided aspiration cytology.

CT scan reveals metastatic adenopathy by central necrosis and extracapsular spread by enhancement of the nodal capsule. MRI is less precise than CT scan in identifying tumor necrosis and extracapsular spread, but MRI is better in assessing enlarged LNs that do not necessarily represent metastasis. Both techniques are incapable of detecting lymph nodes smaller than 1 cm. which, on occasion, independently of the size, are involved in metastasis. Ultrasound-guided aspiration cytology has a higher specificity than either CT or MRI in analyzing lymph nodes, particularly in smaller nodes of less than 10 mm. However, the yield of this technique is directly related to the experience of the ultrasonographer and the pathologist.

Positron emission tomography (PET) has been used recently to assist in the diagnosis of LN metastasis. PET provides information about the metabolic activity of the tissues. Tissues with squamous cell carcinoma cells capture¹⁸ fluoro-2-deoxy-D-glucose (FDG) at increased rates compared to normal tissues. Therefore, a minimal amount of tumor tissue must be present to be positive and its precision is limited in tumors smaller than 1 cm. The precision of PET is limited to around 5 mm.

Recent literature has demonstrated the higher sensitivity and specificity of the (FDG)–PET compared with ultrasonography, CT scan and MRI in the assessment of metastatic staging of neck carcinomas. This finding could signify a positive role for PET in the identification of metastatic disease in patients with a clinically N0 neck. PET findings could provide early diagnosis of recurrent head and neck cancer, as well as indicate the status of the neck after chemo-radiotherapy.

New challenges have been recognized in the last 15 years with the selection of candidates for neck dissection who were treated initially with organ preservation treatment protocols and who may have persistence of neck disease after the nonoperative management. This group of patients can benefit greatly from the routine use of posttreatment PET/CT during their assessment for subsequent surgical management of the neck.

PET and PET/CT are discussed further in Workup.

Histologic examination

Intraoperative findings are important in the supraomohyoid neck dissection. An intraoperative evaluation by the surgeon or pathologist can alter the course of surgery. The criterion standard for detection of LN metastasis in the neck is careful histologic examination and evaluation of all nodes by the pathologist after the neck dissection is completed.

Detection and accurate staging of neck metastasis are extremely important because staging has major implications for prognosis and treatment. Head and neck surgeons at the Memorial Sloan-Kettering Hospital originally developed the most widely accepted terminology used to define regions of involvement of cervical LN groups. The terminology is as follows:

• Region/level I - Submental and submandibular nodes

  • Ia - Nodes in the submental triangle bound by the anterior belly of the digastric muscle and the hyoid bone

  • Ib - Nodes in the triangle bound by the anterior and posterior bellies of the digastric muscle and body of the mandible

• Region/level II - Upper jugular LNs (including the jugulodigastric nodes)

  • IIa - Nodes in the region anterior to the spinal accessory nerve

  • IIb - Nodes in the region posterior to the spinal accessory nerve

• Region/level III - Nodes from the carotid bifurcation to the omohyoid muscle

• Region/level IV - Nodes of the lower jugular area that extend from the omohyoid to the clavicle

• Region/level V - All LNs within the posterior triangle of the neck

• Region/level VI - Nodes in the anterior compartment group, which includes the LNs that surround the midline structures of the neck (These nodes extend from the hyoid bone superiorly to the suprasternal notch inferiorly.)

The revisions proposed by the American Head and Neck Society and the American Academy of Otolaryngology Head and Neck Surgery Committee and published in 2002 recommended the use of 6 neck levels and 6 sublevels, which added 2 extra sublevels (a and b) at level V. The 6 sublevels are Ia (submental nodes), Ib (submandibular nodes), IIa and IIb (upper jugular nodes), Va (spinal accessory nodes), and Vb (transverse cervical and supraclavicular nodes). ^{[4, 5]}

No single set of indications exists for supraomohyoid neck dissection. They vary among authors and institutions around the world. Management strategies discussed in this article are based on recent publications. However, no medical dogma exists and the need for a particular surgery should be based on a case-by-case evaluation that considers the condition of the patient, the surgeon’s expertise and the institution’s capabilities.

N0 neck/squamous cell carcinoma of the oral cavity

The current general opinion is that selective neck dissection is a good alternative for the N0 neck in persons with squamous cell carcinoma (SCC) of the oral cavity. ^[10] Therefore, supraomohyoid neck dissection is commonly used for this purpose, if the primary lesion is not treated with radiation therapy. ^[9]

An extended supraomohyoid neck dissection that involves the removal of lymph nodes from levels I through IV has been advocated by certain surgeons if the primary lesion involves the oral tongue subunit. These surgeons have found that approximately 16% of patients with oral tongue lesions develop level IV metastasis, skipping the lower levels. Conversely, other surgeons have found only 2% of patients with metastasis at level IV in T1-T3 N0 oral tongue cancer and they believe in excising level IV only when intraoperative suspicion of metastasis is found at level II or III. Other surgeons believe that if the intraoperative pathology evaluation reveals metastasis at any level an extended supraomohyoid dissection must be performed. However, apart from these differences, most authors agree that supraomohyoid neck dissection for SCC of the oral cavity with an N0 neck is as effective as radical neck dissection. ^[11]

N+ neck/squamous cell carcinoma of the oral cavity

Indications are less clear in the clinically N+ neck for SCC of the oral cavity. Standardization is lacking. ^[12] Some authors do not advocate a supraomohyoid neck dissection for the N+ neck. Other authors believe that a supraomohyoid neck dissection is effective for the N1 neck and even the N2a neck in carefully selected patients. Most authors generally agree, however, that the presence of metastatic neck nodes cuts the survival rates by half. In the authors’ institution, in the case of an N+ neck with an oral cavity primary tumor, whenever possible we use the comprehensive neck dissection, which involves dissection of levels I through V.

Possible bilateral neck metastasis/ squamous cell carcinoma of the oral cavity

A consensus believes that a bilateral supraomohyoid neck dissection is indicated when the location of the primary tumor SCC of the oral cavity has a high risk of developing metastasis in both sides of the neck, (eg, floor of the mouth, ventral or midline dorsal tongue) and postoperative radiation therapy is not planned.

Facial carcinoma, squamous cell carcinoma, and basal cell carcinoma

The literature provides no clear consensus regarding nonmelanocytic facial carcinomas. Therefore, treatment depends mostly on the size of the primary tumor. Some authors perform a supraomohyoid neck dissection in the early stages of SCC of the lip and skin of the cheek. A bilateral neck dissection is done if the tumor is close to the midline.

An understanding of the relevant neck anatomy is required to perform a supraomohyoid neck dissection adequately. From the surgical point of view, each side of the neck is divided into 2 cervical triangles (ie, anterior, posterior).

Anterior cervical triangle

The inferior border of the mandible, the SCM muscle, and the strap muscle form the anterior cervical triangle. This triangle is subdivided into 4 smaller triangles (ie, submandibular, submental, muscular, carotid). Understanding and identifying each of these areas guides the surgeon in completely removing the contents of the anterior cervical triangle.

• Submandibular triangle: The inferior border of the mandible and the 2 bellies of the digastric muscle delineate the submandibular triangle. The mylohyoid and hyoglossus muscles form the floor. The submandibular area contains the submandibular gland, lymphatic structures, anterior facial vein, and facial artery. The lingual nerve is above the muscular floor and below the deep layer of the deep cervical fascia.

• Submental triangle: The anterior belly of the digastric muscle, the hyoid bone, and the midline of the neck delineate the submental triangle. The mylohyoid muscle forms the floor of the submental triangle, which contains a few LNs and small tributaries of the anterior jugular vein.

• Muscular triangle/carotid triangle: The omohyoid muscle in the anterior cervical triangle delineates the muscular triangle below and the carotid triangle above.

Posterior cervical triangle

The posterior cervical triangle also is referred to as the lateral cervical triangle. This triangle is limited by the anterior margin of the trapezius muscle, the posterior border of the SCM muscle, and the middle third of the clavicle. The posterior aspect of the omohyoid muscle further subdivides the posterior cervical triangle into 2 smaller triangles: the occipital triangle located above the omohyoid muscle and the supraclavicular triangle located inferiorly to the muscle.

Cervical lymph nodes

Cervical LNs are divided into superficial and deep chains. Superficial LNs are involved in a late stage of cancer; therefore, superficial LNs have less oncologic importance. Deep cervical LNs receive drainage from areas of the mouth, pharynx, larynx, salivary glands, thyroid, and the skin of the head and neck. These deep cervical LNs (ie, superior, middle, inferior) accompany the IJV and its branches.

Oncologically, the superior jugular nodes (the group that lies near the anterosuperior aspect of the accessory nerve) are crucial. These nodes represent the most difficult area in the resection of the deep jugular nodes.

The cervical LNs localized in the posterior triangle of the neck are classified into upper, middle, and inferior cervical nodes. Posterior triangle nodes are located beneath the upper portion of the SCM muscle and run posteriorly along the course of the spinal accessory nerve. This group of lymphatics receives drainage from the nasopharynx and communicates directly with the upper deep nodes from the IJV.

The posterior triangle nodes in the inferior aspect progress anteriorly to the supraclavicular area to join the IJV at the base of the neck. The above groups are easier to understand when divided into levels or zones, as follows:

• level I - Nodal group that involves submental and submandibular regions (also referred to as IA and IB)

• level II - Upper jugular group (IIa nodes in the region anterior to the spinal accessory nerve, IIb nodes in the region posterior to the spinal accessory nerve)

• level III - Middle jugular group

• level IV - Lower jugular group

• level V - Posterior triangle group (Va spinal accessory nodes, Vb transverse cervical and supraclavicular nodes)

• level VI - Central anterior neck group

Platysma muscle

The rectangular and sheetlike platysma muscle extends obliquely from the upper chest to the lower face, from posteroinferior to anterosuperior. Its undersurface creates an ideal plane in which to elevate the skin flaps in neck dissection. The platysma muscle is deficient in the lower anterior midline in the neck and posterior to the external jugular vein (EJV) and greater auricular nerve.

Sternocleidomastoid muscle

The SCM muscle runs from anteroinferior to posterosuperior and attaches to the mastoid tip. The greater auricular nerve and the EJV cross the upper aspect of the muscle. These structures guide the surgeon to the right plane of dissection and should be left on the surface of the SCM during flap elevation. The fascial envelope of the muscle is a key structure for selective neck dissections.

Spinal accessory nerve

The spinal accessory nerve crosses over the IJV in approximately 70% of individuals. The nerve is also medial to the posterior belly of the digastric and stylohyoid muscles. Anatomic variations include the nerve that runs medially to the IJV in 30% of individuals and through the vein in 3% of individuals. Attention to this fact avoids damage to the IJV during the dissection of cranial nerve XI in the upper aspect of the neck. The nerve enters obliquely to the SCM muscle, from superior to inferior, with the exit at the Erb point, which is near the greater auricle nerve at the posteroinferior edge of the SCM muscle.

Digastric muscle

The posterior belly of the digastric muscle is an important landmark. This belly extends from the hyoid bone to the undersurface of the mastoid tip. Important and delicate structures are recognized medial to the muscle. Therefore, the posterior belly of the digastric muscle lies superficial to the external and internal carotid arteries, hypoglossal nerve, and IJV. Lateral to the posterior belly of the digastric muscle, the only structure that requires preservation is the marginal mandibular nerve.

Marginal mandibular nerve

The marginal mandibular nerve is localized deep to the superficial layer of the deep cervical fascia that covers the submandibular gland and lies superficial to the anterior facial vein. The best way to preserve the nerve is to identify it carefully at the above locations. Once the nerve is identified, tissue lateral and inferior to the nerve can be divided to expose the posterior belly of the digastric muscle.

Trapezius muscle

The trapezius muscle extends from the posterior occiput to the lateral third of the clavicle. The anterior border of the trapezius is the posterior edge of level V, or the posterior triangle, of the neck.

Omohyoid muscle

Like the digastric muscle, the omohyoid muscle has 2 bellies. The anterior belly is superficial to the IJV. The posterior belly is superficial to the brachial plexus, phrenic nerve, and transverse cervical artery and vein. Like the digastric muscle, the omohyoid is a key anatomic landmark in radical neck dissection.

Hypoglossal nerve and vagus nerve

The vagus nerve in the neck is intimately associated with the carotid sheath and lies immediately deep to the IJV. Intraoperatively, the vagus nerve can be injured during dissection and division of the lower portion of the IJV. Identification of the vagus nerve before division of the IJV is mandatory.

The hypoglossal nerve in the neck travels under the IJV, passes over the internal and external carotid arteries, and continues inferomedially to the posterior belly of the digastric muscle to enter the tongue musculature. Identification is important to avoid injury.

Brachial plexus and phrenic nerve

The phrenic nerve lies above the anterior scalene muscle and deep to the transverse cervical artery. The brachial plexus exits lower in the neck and then passes between the anterior and middle scalene muscles. Identify anterior and middle scalene muscles before clamping lymphatic structures. Avoid dissection in the supraclavicular area before phrenic and brachial plexus visualization.

Thoracic duct

The thoracic duct, located in the lower left neck, arises posterior to the IJV and anterior to the phrenic and transverse cervical artery. The anatomy varies, and the duct has multiple interdigitated channels.

See Neck Anatomy, Vagus Nerve Anatomy, Brachial Plexus Anatomy, and Thoracic Duct Anatomy for more information.

The contraindications to supraomohyoid neck dissection are obvious once the indications are understood.

In summary:

• The indications to supraomohyoid neck dissection are SCC of the oral cavity, T1-T4, and N0. Supraomohyoid neck dissection is both diagnostic and therapeutic in patients with N0. On this point, authors generally agree.

• However, the treatment role of supraomohyoid neck dissection in patients with positive neck disease (N+) is more controversial. Some authors consider the supraomohyoid neck dissection an adequate treatment for selected N1 and N2a necks. Other authors, however, favor extending the dissection to levels IV and V.

Therefore, the contraindication to supraomohyoid neck dissection is any SCC of the oral cavity in which the clinical neck stage is other than. N0, N1, or N2a.