Lymph Node Distribution Nodal Groups

For practical reasons, the neck may be artificially divided into different lymph node regions. This does not mean that there is a true anatomical or physiological separation within the lymphatic system of the neck. Not only is there no physical separation within the lymphatic system of the neck, but a widespread interconnection exists between the different nodal chains, as already described. Thus, the regional lymph node classification should be regarded only as a schematic representation of the lymphatic system of the neck, and not as an anatomical transcription of the reality. As often happens in medicine, nature is much more complex than we would like it to be.

The most popular terminology for subdividing the lymph node groups was proposed in 1991 by the Committee for Head and Neck Surgery and Oncology of the American Academy of Otolaryngology—Head and Neck Surgery. This committee worked to define the anatomical boundaries of lymph node groups to offer fundamental principles for a classification of neck dissection procedures. The neck is divided into six different levels (Figs. 2-6A, 2-6B).

• Level I: Submental and submandibular nodes. This group includes the lymph nodes located within the submental triangle, bounded by the anterior belly of the digastric muscle and the hyoid bone. The submandibular group includes the lymph nodes located within the boundaries of

Lymph Node DistributionLymph Gland Distribution

Figure 2-6 Regional division of the lymphatic system of the neck according to the classification of the American Academy of Otolaryngology—Head and Neck Surgery. (A) Lateral view. (B) Anterior view. Level I, submental and submandibular region; Level II, upper jugular region; Level III, middle jugular region; Level IV, lower jugular region; Level V, posterior triangle; Level VI, anterior compartment.

Figure 2-6 Regional division of the lymphatic system of the neck according to the classification of the American Academy of Otolaryngology—Head and Neck Surgery. (A) Lateral view. (B) Anterior view. Level I, submental and submandibular region; Level II, upper jugular region; Level III, middle jugular region; Level IV, lower jugular region; Level V, posterior triangle; Level VI, anterior compartment.

the anterior and posterior bellies of the digastric muscle, the stylohyoid muscle, and the body of the mandible. The submandibular gland, which is located within this cervical space, should be removed when this nodal group is included in the resection.

• Level II: Upper jugular nodes. This group contains the lymph nodes located around the upper third of the internal jugular vein and the spinal accessory nerve. It goes from the level of the skull base superiorly to the level of the inferior border of the hyoid bone and carotid bifurcation inferiorly. The posterior boundary is the posterior border of the sternocleidomastoid muscle, and the anterior boundary is the lateral border of the sternohyoid and stylohyoid muscles.

• Level III: Middle jugular nodes. This group includes the lymph nodes located around the middle third of the internal jugular vein. The boundaries of this space are the inferior border of the hyoid bone and the carotid bifurcation superiorly, the inferior border of the cricoid cartilage and the junction of the omohyoid muscle with the internal jugular vein inferiorly, the posterior border of the sternocleidomastoid muscle posteriorly, and the lateral border of the sternohyoid muscle anteriorly.

• Level IV: Lower jugular nodes. This nodal group contains the lymphatic structures located around the lower third of the internal jugular vein. Its boundaries are the inferior border of the cricoid cartilage and the omohyoid muscle superiorly, the clavicle inferiorly, the posterior border of the sternocleidomastoid muscle posteriorly, and the lateral border of the sternohyoid muscle anteriorly.

• Level V: Posterior triangle. This group includes the lymph nodes located along the transverse cervical artery and lower half of the spinal accessory nerve as well as the supraclavicular lymph nodes. The boundaries are the anterior border of the trapezius muscle posteriorly, the posterior border of the sternocleidomastoid muscle anteriorly, the clavicle inferiorly, and the convergence of the sternocleidomastoid and trapezius muscles superiorly.

• Level VI: Anterior compartment. This level contains the pre- and paratracheal nodes, precricoid (Delphian) node, perithyroidal nodes, and the lymph nodes along the recurrent laryngeal nerves. The boundaries are the hyoid bone superiorly, the suprasternal notch inferiorly, and the carotid arteries laterally.

• Level VII. Some authors consider this an additional area. It includes the upper mediastinal lymph nodes located below the suprasternal notch.

One of the main theoretical advantages of the nodal group classification is that every group of nodes may be related to different head and neck structures in order to assess the potential risk for metastasis for every primary location. However, the predictable lymph flow pattern that occurs under normal conditions may be modified by factors related to the tumor itself, the anatomical characteristics of the patient, and the influence of external factors such as previous treatment. Thus, reducing the field of dissection should be carefully planned according to the personal experience of the surgeon and the clinical features of the patient. Table 2-1 shows the relationship between the location of the primary tumor and the nodal groups at greatest risk for harboring metastases.

Division of Nodal Groups by Subzones

A new modification of the nodal group classification has been recently proposed. This update of the original classification includes a subzone separation for some of the original levels and uses anatomical structures depicted radiologically to define boundaries between various neck levels to accurately designate image-depicted nodes (Figs. 2-7A, 2-7B).

Level I is subdivided into

• IA: submental lymph nodes

• IB: submandibular lymph nodes

Submental Lymph Node Distribution

Figure 2-7 Division of nodal groups by subzones. (A) Lateral view. (B) Anterior view. Ia, submental nodes; Ib, submandibular nodes; IIa, upper jugular nodes anterior to the eleventh nerve; IIb, upper jugular nodes posterior to the eleventh nerve; Va, lymph nodes in the posterior triangle located above the level of the inferior border of the cricoid cartilage; Vb, lymph nodes in the posterior triangle located below the level of the inferior border of the cricoid cartilage.

Figure 2-7 Division of nodal groups by subzones. (A) Lateral view. (B) Anterior view. Ia, submental nodes; Ib, submandibular nodes; IIa, upper jugular nodes anterior to the eleventh nerve; IIb, upper jugular nodes posterior to the eleventh nerve; Va, lymph nodes in the posterior triangle located above the level of the inferior border of the cricoid cartilage; Vb, lymph nodes in the posterior triangle located below the level of the inferior border of the cricoid cartilage.

TABLE 2-1. Nodal Groups at Greatest Risk of Developing Metastases According to the Location of the Primary Tumor

Nodal Region

Location of the Primary Tumor

Area I:

Submental nodes

Floor of mouth, anterior oral tongue, anterior mandibular alveolar ridge, lower lip

Submandibular nodes

Oral cavity, anterior nasal cavity, soft tissue structures of the midface, subman-

dibular gland

Area II: Upper jugular nodes

Oral cavity, nasal cavity, nasopharynx, oropharynx, hypopharynx, larynx,

parotid gland

Area III: Middle jugular nodes

Oral cavity, nasopharynx, oropharynx, hypopharynx, larynx

Area IV: Lower jugular nodes

Hypopharynx, larynx, cervical esophagus

Area V: Posterior triangle

Nasopharynx, oropharynx

Area VI: Anterior compartment

Thyroid gland, larynx (glottic and subglottic), apex

of the piriform sinus, cervical esophagus

Area VII: Upper mediastinal group

Thyroid, larynx (glottic and subglottic), lung

Level II is subdivided into

• Level IIA: lymph nodes located anterior to the vertical plane defined by the spinal accessory nerve

• Level IIB: lymph nodes located posterior to the vertical plane defined by the spinal accessory nerve

Level V is subdivided into

• Level VA: lymph nodes located above the horizontal plane defined by the inferior border of the cricoid cartilage. This subzone includes part of the lymph nodes of the spinal accessory chain.

• Level VB: lymph nodes located below the horizontal plane defined by the inferior border of the cricoid cartilage. This subzone includes the lymph nodes of the transverse cervical chain.

With this modification, each side of the neck actually has nine different lymphatic regions. Their combination with the various T and N stages results in a huge number of different possibilities, which seem impractical, at least, for teaching purposes.

A Final Comment on the Nodal Group Classification

The main use of the nodal group classification is to support the worthiness of selective neck dissections. However, the artificial nature of the division creates some inconsistencies that must be kept in mind to avoid falling into a ''nodal group fundamentalism,'' which often happens nowadays. In our opinion, the following are the main weak points of the artificial division of the neck into nodal regions.

1. There is a notorious lack of anatomical landmarks to identify most boundaries of the proposed regions. This makes it very difficult to compare results, even if we all use the same classification. This situation has been aggravated by the recent introduction of subzones whose boundaries are especially difficult to delineate at surgery and for pathological analysis. The well-defined theoretical, anatomical, and radiological boundaries of some of the various levels and subzones are distorted at surgery by the operative maneuvers. It is not unusual to decide to stop the dissection at a given point to find later that more tissue than desired has been removed because too much traction has been used during the dissection. On the other hand, even in the ideal situation, one person's upper level IV lymph node may easily be another's lower level III node. This is even more probable with the subzone division of the new classification.

2. Under normal conditions the lymph flow follows a rather predictable course that is used as an argument to support the oncological safety of selective dissections. However, head and neck cancer patients do not fully satisfy the criteria of ''normal conditions,'' thus making selective neck dissections a controversial issue. Some operations have stood the test of time and can be considered positively safe from an oncological standpoint. Others still need documented proof of efficacy. Meanwhile, the use of selective operations should be cautiously recommended. Experience is the key factor to successful selective neck dissection.

3. Finally, the ultimate rationale for selective operations should not be sought on the nodal region subdivision, but on the functional concept. If selective neck dissections are useful — and for some of them this is a fact — it is because the functional concept is a reality. We can remove the lymphatic tissue from the neck without the need to remove adjacent cervical structures. The exact limits of this removal for every single head and neck tumor have not been determined with certainty and require further studies and well-designed investigations.

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