Neck Lymph Node Dissection

March

Classification of Cervical Lymph Node Levels

Cervical lymph nodes include the submental, submandibular, anterior cervical, superficial cervical, and deep cervical lymph nodes. Based on patterns of cervical lymph node metastasis and the requirements for neck dissection, the American Academy of Otolaryngology–Head and Neck Surgery divided cervical lymph nodes into six levels in 1991. A seventh level, corresponding to the superior mediastinal lymph nodes, was later added. The levels are described as follows:

Level I: Includes submental and submandibular lymph nodes.
Level II: Consists of the upper group of internal jugular lymph nodes, extending from the skull base to the level of the hyoid bone. The anterior border is the lateral margin of the sternohyoid muscle, and the posterior border is the posterior edge of the sternocleidomastoid muscle. Based on the relationship to the accessory nerve, Level II is further divided into Level IIA and Level IIB.
Level III: Comprises the middle group of internal jugular lymph nodes, which extend from the hyoid bone to the intersection of the omohyoid muscle and internal jugular vein. The anterior and posterior borders are the same as for Level II.
Level IV: Includes the lower group of internal jugular lymph nodes, extending from the intersection of the omohyoid muscle and internal jugular vein to the clavicle. The anterior and posterior borders are the same as for Level II.
Level V: Consists of the lymph nodes in the posterior triangle of the neck, including the supraclavicular nodes. The anterior border is the posterior edge of the sternocleidomastoid muscle, the posterior border is the anterior margin of the trapezius muscle, and the inferior border is the clavicle.
Level VI: Includes the anterior cervical lymph nodes, such as the prelaryngeal, paratracheal, and perithyroid lymph nodes. The lateral borders are the common carotid arteries, the superior border is the hyoid bone, and the inferior border is the suprasternal notch.
Level VII: Represents the superior mediastinal lymph nodes, located in the anterior superior mediastinum and the tracheoesophageal groove. These nodes extend from the suprasternal notch to the brachiocephalic trunk.

Assessment and Classification of Cervical Lymph Node Metastases

The evaluation of cervical lymph node metastases typically utilizes clinical examinations such as neck palpation alongside imaging modalities including ultrasonography, CT, and MRI. These methods are used to assess the location, size, number, and the presence of extranodal extension (ENE) in cervical lymph nodes.

Among these techniques, neck ultrasonography is notable for its high sensitivity and specificity, non-invasive nature, and cost-effectiveness. It can detect metastatic lymph nodes smaller than 1 cm, including occult metastases. Contrast-enhanced CT is effective in delineating the position of cervical lymph nodes and their spatial relationship with adjacent structures, such as blood vessels. MRI provides a more precise visualization of the extent of metastatic involvement. For suspected metastatic cervical lymph nodes with an unknown primary tumor, fine-needle or core-needle aspiration biopsy under ultrasound guidance can confirm the diagnosis.

According to the 8th edition of the TNM staging system for head and neck malignancies published by the American Joint Committee on Cancer (AJCC) and the Union for International Cancer Control (UICC), the clinical staging of cervical lymph nodes for head and neck malignancies such as laryngeal cancer, hypopharyngeal cancer, oral cavity cancer, and p16-negative oropharyngeal cancer is categorized as follows:

N_x: Regional lymph nodes cannot be evaluated.
N₀: No regional lymph node metastasis.
N₁: Metastasis in a single ipsilateral lymph node, with a maximum diameter ≤3 cm, and no extranodal extension (ENE).
N₂: Metastasis in a single ipsilateral lymph node with a maximum diameter >3 cm but ≤6 cm, and ENE (-); or, metastasis in multiple ipsilateral lymph nodes, all with a maximum diameter ≤6 cm, and ENE (-); or, metastasis in bilateral or contralateral lymph nodes, all with a maximum diameter ≤6 cm, and ENE (-).
N_2a: Metastasis in a single ipsilateral lymph node with a maximum diameter >3 cm but ≤6 cm, and ENE (-).
N_2b: Metastasis in multiple ipsilateral lymph nodes, all with a maximum diameter ≤6 cm, and ENE (-).
N_2c: Metastasis in bilateral or contralateral lymph nodes, all with a maximum diameter ≤6 cm, and ENE (-).
N₃: Metastasis in any single lymph node with a maximum diameter >6 cm, and ENE (-); or, metastasis in any lymph node with clinically evident ENE (+).
N_3a: Metastasis in a single lymph node with a maximum diameter >6 cm, and ENE (-).
N_3b: Metastasis in any lymph node with clinically evident ENE (+).

Classification of Neck Lymph Node Dissection

Neck lymph node dissection, or neck dissection, is an important treatment method for managing cervical lymph node metastases in head and neck malignancies. The classification includes the following:

Radical Neck Dissection (RND)

This involves the removal of lymph nodes from Levels I to V without preserving the sternocleidomastoid muscle, internal jugular vein, and accessory nerve.

Modified Radical Neck Dissection (Modified RND)

This involves the removal of lymph nodes from Levels I to V while preserving at least one of the following structures: the sternocleidomastoid muscle, internal jugular vein, or accessory nerve.

Selective Neck Dissection (SND)

This preserves at least one group of cervical lymph nodes. Examples include:

Supraomohyoid dissection (Levels I–III)
Extended supraomohyoid dissection (Levels I–IV)
Lateral neck dissection (Levels II–III or II–IV)
Posterolateral neck dissection (Levels II–V along with surrounding soft tissues near the tumor)
Central compartment dissection (Level VI, with or without Level VII)

Extended Radical Neck Dissection (Extended RND)

This includes the removal of lymph nodes from Levels I to V or Level VI, along with any tissues invaded by the tumor, such as the common carotid artery, vagus nerve, or paraspinal muscles.

Treatment Principles for Cervical Lymph Nodes in Head and Neck Squamous Cell Carcinoma

For patients undergoing primary tumor resection for head and neck squamous cell carcinoma, neck dissection is usually performed concurrently to manage lymphatic metastases. The choice of neck dissection strategies should be based on the status of cervical lymph nodes and the primary tumor (T) stage, as these vary according to the tumor's anatomical location.

Complications of Neck Lymph Node Dissection and Their Management

Hemorrhage

Intraoperative bleeding often results from injury to the internal jugular vein or loosening of ligature sutures. The thin venous walls can be easily damaged during dissection, leading to postoperative secondary bleeding. Loosening of ligature sutures may occur due to insufficient surgical skill, the use of overly coarse sutures, or suture breakage. Postoperative coughing can also increase intravascular pressure, causing ligature slippage or rupture of small blood vessels. Minor bleeding can be managed with compression bandaging. However, significant bleeding may require a second surgical exploration to locate the damaged site, followed by repair or re-ligation. Prompt recognition and management of postoperative bleeding are essential, as undetected hematomas may lead to respiratory distress, infection, or delayed wound healing.

Wound Infection

Wound contamination by secretions during primary tumor resection, such as in total laryngectomy with concurrent neck dissection, is a major cause of infection. Additional factors include hematoma in the surgical cavity, improper antibiotic use, or pharyngeal fistula formation. Infection necessitates early drainage and bacterial culture with sensitivity testing to identify appropriate antibiotics. In severe cases, particularly following salvage surgery after radiotherapy, wound infections can result in carotid artery rupture and fatal hemorrhage.

Chyle Leak

Injury to the thoracic duct during left-sided neck dissection is a possible cause. Intraoperative thoracic duct injury should be ligated. Postoperative chyle leak can be managed with a low-fat diet and local compression bandaging. Persistent or high-volume leaks lasting more than one week may require reopening the wound to locate and ligate the thoracic duct.

Air Embolism

Damage to the internal jugular or subclavian vein and its large branches may lead to air entering the venous system due to negative intrathoracic pressure, resulting in air embolism. This is a potentially life-threatening complication, characterized by symptoms such as rapid-onset dyspnea and cyanosis, and may result in immediate death in severe cases. Management involves compressing the proximal venous site with saline-soaked gauze to stop air entry, followed by repair of the vessel and re-ligation.

Salivary Fistula

This complication typically arises from incomplete or improper suturing after removal of the inferior portion of the parotid gland. Pressure bandaging over a few days often leads to resolution, while persistent salivary fistulae may require surgical repair.

Pneumothorax

Pneumothorax may occur due to unintentional damage to the pleural dome during dissection. Bedside chest X-rays should be performed if pneumothorax is suspected. Management depends on severity; minor cases may be closely monitored without intervention, while severe cases with associated dyspnea require thoracentesis or closed thoracic drainage.