Lymph nodes are small, bean-shaped organs that filter lymph fluid throughout the body. These structures house immune cells that help trap and destroy foreign substances like bacteria and cancer cells. Clinicians categorize the lymph nodes in the neck, known as the cervical lymph nodes, into a standardized anatomical classification system (Level I through Level VI). This system allows for precise communication regarding the location of disease. Level V is a specific group designated for nodes situated in the posterior region of the neck.
Anatomical Location and Subdivisions
Level V lymph nodes occupy the posterior triangle of the neck. The nodes are located behind the sternocleidomastoid muscle, which forms the anterior border. The posterior border is the anterior edge of the trapezius muscle, and the inferior border is the clavicle.
These nodes are closely associated with the spinal accessory nerve and the transverse cervical vessels. The Level V region is subdivided into V-A and V-B, marked by a horizontal line passing through the inferior border of the cricoid cartilage.
Level V-A, the superior portion, contains nodes around the spinal accessory nerve. Level V-B, the inferior portion, includes the supraclavicular nodes, which sit just above the clavicle. This mapping is important because the location of a metastatic node often suggests the site of the primary tumor.
Role in Cancer Staging
Involvement of Level V lymph nodes is important for cancer planning and prognosis. Level V nodes are at risk for metastasis from cancers originating in the posterior scalp, posterior neck skin, and the nasopharynx. Nasopharyngeal carcinoma frequently metastasizes to this level. Thyroid, oropharyngeal, or laryngeal cancers also spread to Level V.
In the TNM staging system, the ‘N’ category describes regional lymph node involvement. Metastasis to Level V generally results in a higher ‘N’ classification compared to limited disease in the anterior levels. This higher staging reflects a greater volume of disease and a less favorable outlook.
The chance of cancer spreading directly to Level V without first involving the common upstream nodes (Levels I-IV) is low for most head and neck squamous cell carcinomas. This is known as a “skip” metastasis. However, for tumors of the posterior scalp or nasopharynx, Level V can be the first site of spread.
Extracapsular spread (ECS) is frequently associated with Level V involvement. ECS means the cancer has broken through the lymph node’s outer capsule and invaded the surrounding tissue. The presence of ECS is a negative prognostic factor, indicating a higher risk of recurrence and reduced long-term survival.
Diagnostic Imaging and Assessment
Assessment for metastatic disease in Level V nodes begins with a physical examination for palpable masses. Imaging modalities are necessary to evaluate nodes that are too small or deep to be felt. Ultrasound (US) is often the initial tool, providing high-resolution images and allowing for size measurement.
Nodes are considered suspicious if they exceed a size threshold, a short-axis diameter greater than 10 millimeters. Other concerning features include a rounded shape, loss of the normal fatty hilum, or central necrosis. If suspicious features are seen, an ultrasound-guided fine-needle aspiration (FNA) biopsy is performed for pathological confirmation.
Computed Tomography (CT) and Magnetic Resonance Imaging (MRI) evaluate the full extent of the disease. CT scans are effective at identifying central necrosis, which appears as a dark area within the node. On MRI, signs of extracapsular spread can be visualized, such as irregular nodal margins, infiltration into the adjacent fat, or loss of the clear plane between the node and nearby muscles.
Positron Emission Tomography (PET) combined with CT assesses the metabolic activity of the nodes. Cancer cells typically have a higher metabolic rate than normal tissue, causing them to absorb the radioactive tracer. This modality is valuable for detecting small, non-enlarged nodes that may be metabolically active, particularly in the Level V and supraclavicular regions.
Treatment Implications and Procedures
A confirmed diagnosis of metastatic disease in Level V requires a neck dissection. When Level V is involved, a Modified Radical Neck Dissection (MRND) or a Radical Neck Dissection (RND) is necessary, as these procedures clear all lymph node levels (I through V). The MRND removes lymph nodes while attempting to preserve non-lymphatic structures like the spinal accessory nerve, internal jugular vein, and sternocleidomastoid muscle, reducing post-operative side effects.
If the primary tumor suggests a high risk of Level V involvement, such as posterior scalp tumors, a Selective Neck Dissection (SND) targeting the posterolateral regions (Levels II-V) may be performed. The extent of the surgery is determined by the location and aggressiveness of the primary cancer and the distribution of the metastatic nodes. Complete removal of the diseased tissue while minimizing morbidity is the goal.
Following surgery, Level V involvement often necessitates adjuvant therapy, most commonly radiation therapy. This is true if the pathology report confirms extracapsular spread (ECS) or if multiple nodes are involved. Radiation is applied to the neck region to eliminate any microscopic cancer cells. The presence of ECS in a Level V node is a primary indicator for post-operative radiation, as it is a high-risk feature for local recurrence.