Lymph nodes are part of the body’s immune system, acting as small filters that trap viruses, bacteria, and other threats. They can swell for many reasons, most often in response to a common infection. When a neck lump persists or raises concern, physicians use diagnostic imaging to investigate. An ultrasound is the most common first step, providing a safe and effective way to look beneath the skin to examine the swollen lymph node.
The Role of Ultrasound in Evaluating Neck Lymph Nodes
Ultrasound imaging, also known as sonography, uses high-frequency sound waves to create real-time pictures of the body’s interior. It is a preferred method for evaluating neck lymph nodes because it is non-invasive, meaning it does not require cuts or injections, and it does not use ionizing radiation like X-rays or CT scans. This safety profile makes it suitable for all patients, including those requiring repeated imaging. The live images allow an operator to dynamically see the structure and blood flow within the lymph node.
A patient undergoing a neck ultrasound can expect a straightforward and painless process. The individual lies down on an examination table, and a clear, water-based gel is applied to the skin over the area of concern. This gel helps transmit sound waves from a handheld device, called a transducer, into the body. A radiologist or sonographer gently presses the transducer against the skin, moving it to capture images from different angles, providing immediate visual information.
Ultrasound Characteristics of Benign Lymph Nodes
Several features on an ultrasound image suggest a lymph node is benign, or non-cancerous. One of the primary characteristics is its shape. Benign nodes are oval or elongated, appearing flatter than they are wide, which is measured by a long-axis to short-axis ratio. A ratio greater than 2 is a reassuring sign, and the borders of these nodes are also smooth and clearly defined.
Another indicator of a healthy, benign lymph node is the presence of a fatty hilum. The hilum is the central part of the node where blood vessels and lymphatic fluid enter and exit. On an ultrasound, this structure appears as a bright, linear area in the center of the node, a feature described as “echogenic.” The visibility of this central fatty hilum is a sign that the internal architecture of the lymph node is normal.
The outer layer of the lymph node, called the cortex, provides additional clues. In a benign node, the cortex is thin and has a uniform thickness. When Doppler ultrasound is used to assess blood flow, a benign node will show an orderly vascular pattern. Blood vessels are seen entering and leaving through the central hilum, which is consistent with the normal function of a healthy lymph node.
Ultrasound Features Suggesting Malignancy
Conversely, certain ultrasound findings raise suspicion for malignancy. These features include:
- Shape and Borders: Malignant nodes tend to become rounder as they fill with cancer cells, resulting in a long-axis to short-axis ratio of less than 2. Their borders may also become irregular or ill-defined, suggesting that the cancer could be invading surrounding tissues.
- Loss of Fatty Hilum: The absence of the central, bright echogenic hilum is a concerning feature, as it suggests the node’s internal architecture has been replaced by cancerous tissue. While some benign nodes can lack a visible hilum, its absence combined with other suspicious features is highly indicative of a problem.
- Cortical and Internal Changes: Malignant infiltration can cause the outer cortex to become abnormally thick, either uniformly or in a specific, bulging area. The internal texture may become mixed (heterogeneous), and in some cases, dark, fluid-filled pockets from internal breakdown, known as cystic necrosis, can appear.
- Microcalcifications: The presence of tiny, bright specks within the node is another feature associated with certain types of metastatic cancers, particularly from the thyroid gland.
- Abnormal Blood Flow: Using Doppler ultrasound, a radiologist might observe peripheral or disorganized blood flow, rather than the normal centralized pattern. This altered vascularity suggests the formation of new, abnormal blood vessels to feed the growing tumor.
Interpreting Results and Subsequent Procedures
An ultrasound provides a detailed risk assessment, not a definitive diagnosis. The findings help a radiologist classify a lymph node’s appearance on a spectrum from benign to highly suspicious. Based on this assessment, the referring physician will determine the next course of action. The combination of multiple suspicious features increases the likelihood of malignancy.
If the ultrasound features indicate a benign reactive node, a physician may recommend a “watch and wait” approach. This involves a period of clinical observation or a follow-up ultrasound in a few weeks or months to ensure the node returns to normal or remains stable. This is a common outcome, as most swollen lymph nodes are related to infection.
When ultrasound findings are indeterminate or suspicious for malignancy, a biopsy is the next step to obtain a definitive diagnosis. The most common procedure is a Fine-Needle Aspiration (FNA), which is often performed with ultrasound guidance. During an FNA, a physician uses the live ultrasound image to guide a thin needle into the suspicious lymph node to withdraw a sample of cells.
These collected cells are sent to a pathologist, a doctor who analyzes cells and tissues to identify disease. The pathologist’s examination provides the final diagnosis, confirming whether the cells are benign or malignant. The ultrasound serves as a roadmap, guiding the decision of whether and where to perform a biopsy for the most accurate answer.