Lymph Node on Ultrasound Normal vs Abnormal

Lymph nodes are an essential part of the body’s immune system, helping to fight off infections and diseases. Ultrasound imaging is a common tool used to examine lymph nodes.  Understanding what a normal lymph node looks like on ultrasound and how it differs from an abnormal one is important for early diagnosis of various conditions, including infections, inflammation, and cancer.

In this article, we’ll discuss the key differences between normal and abnormal lymph nodes as seen on ultrasound imaging. We’ll also discuss the various characteristics that radiologists look for when determining whether a lymph node is normal or concerning.

What is Ultrasound Imaging of Lymph Nodes?

Ultrasound imaging, also known as sonography, is a non-invasive imaging technique that uses sound waves to create pictures of structures inside the body. It is widely used to examine lymph nodes because it’s safe, quick, and effective.

During the ultrasound, a small handheld device called a transducer is placed over the area being examined. The transducer sends sound waves into the body and collects the echoes as they bounce back from the tissues, creating an image on the screen.

Characteristics of Normal Lymph Nodes on Ultrasound

When examining lymph nodes on ultrasound, there are several key features that radiologists use to determine if the node appears normal. A normal lymph node typically has specific characteristics that make it easy to identify.

1. Shape and Size

Normal lymph nodes are usually oval or kidney-shaped and have a long-to-short axis ratio of 2:1. They are generally small, measuring less than 1 cm in the short axis diameter. However, the size of a lymph node can vary depending on its location in the body and the patient’s age.

2. Echogenic Hilum

A defining feature of normal lymph nodes is the presence of an echogenic (bright) hilum, which is the central part of the node. The hilum appears bright on ultrasound because it contains fatty tissue and blood vessels. A normal lymph node should have a visible hilum.

3. Homogeneous Texture

Normal lymph nodes have a homogeneous or uniform texture. This means that the tissue within the node appears smooth without irregularities.

4. Well-Defined Borders

Normal lymph nodes typically have well-defined, smooth borders. This means that the edges of the node are clear and distinct from the surrounding tissue. If the borders appear blurred or irregular, this may indicate an abnormality.

Abnormal Lymph Node Characteristics on Ultrasound

Abnormal lymph nodes can appear quite different.  When lymph nodes become enlarged, misshapen, or change in texture, it can be a sign of underlying disease. The changes in ultrasound characteristics can help radiologists determine whether further investigation or treatment is needed.

1. Enlarged Size

One of the most common signs of an abnormal lymph node is enlargement. On ultrasound, a lymph node is considered abnormal if the short axis diameter exceeds 1 cm. Enlarged lymph nodes are often seen in response to infection, inflammation, or malignancy (cancer). However, size alone is not always a definitive indicator of abnormality, as some benign conditions can also cause lymph nodes to enlarge.

2. Loss of the Echogenic Hilum

A concerning feature of abnormal lymph nodes is the loss of the echogenic hilum. If the hilum is absent or difficult to visualize, it can be a sign that the node is not functioning normally. This is often seen in cancerous or metastatic lymph nodes, where the normal architecture of the node has been replaced by abnormal tissue.

3. Heterogeneous Texture

Abnormal lymph nodes often have a heterogeneous or mixed texture on ultrasound. Instead of appearing uniform, the tissue within the node may have dark areas (hypoechoic regions) or appear uneven. This irregular texture can be a sign of infection, inflammation, or malignancy, and often warrants further evaluation.

4. Irregular Borders

Lymph nodes with irregular, poorly defined borders are more likely to be abnormal. Blurred edges can indicate that the node is becoming infiltrated by disease, such as cancer, which disrupts the normal structure of the lymph node. In some cases, malignant lymph nodes may have spiculated or jagged borders, which further raise suspicion.

Key Signs of Malignant Lymph Nodes on Ultrasound

Detecting cancerous lymph nodes is one of the primary reasons for using ultrasound imaging. Certain ultrasound features are strongly associated with malignancy and can help radiologists identify lymph nodes that may need a biopsy or further testing.

1. Round Shape

While normal lymph nodes are typically oval, malignant lymph nodes often take on a more round shape. A lymph node with a round shape (a long-to-short axis ratio close to 1:1) is more likely to be suspicious for malignancy, particularly if it is also enlarged.

2. Increased Vascularity

Cancerous lymph nodes often show increased blood flow when examined with Doppler ultrasound. Increased vascularity occurs because tumors stimulate the growth of new blood vessels to supply them with nutrients. If a lymph node shows abnormal blood flow patterns, particularly in areas outside the hilum, it can be a sign of malignancy.

3. Calcifications

The presence of calcifications, or small deposits of calcium, within a lymph node is another potential indicator of cancer. Calcifications appear as bright white spots on ultrasound and are often seen in metastatic nodes, particularly those from thyroid cancer.

4. Necrosis

Necrosis, or tissue death, can occur within lymph nodes affected by cancer or severe infection. On ultrasound, necrotic areas appear as dark, fluid-filled spaces within the node, indicating that part of the tissue has died. This is a concerning feature that requires further investigation.

Benign vs. Malignant: How Ultrasound Helps Differentiate

Ultrasound plays an important role in differentiating between benign (non-cancerous) and malignant (cancerous) lymph nodes. While no single ultrasound feature can definitively diagnose malignancy, radiologists rely on a combination of characteristics to assess the likelihood of cancer. A normal lymph node will typically have an oval shape, a visible echogenic hilum, homogeneous texture, and well-defined borders. On the other hand, malignant lymph nodes are more likely to be round, lack an echogenic hilum, have a heterogeneous texture, and show abnormal blood flow patterns or calcifications.

Conclusion

Ultrasound imaging is an invaluable tool for evaluating lymph nodes, helping radiologists to distinguish between normal and abnormal nodes based on their size, shape, texture, and other characteristics. A normal lymph node will typically have an oval shape, a visible echogenic hilum, a smooth texture, and well-defined borders. Abnormal lymph nodes, on the other hand, may appear enlarged, misshapen, and irregular, with features such as a loss of the hilum, heterogeneous texture, or abnormal blood flow.

Recognizing these differences is important for early detection of conditions like infection, inflammation, and cancer. When lymph node abnormalities are detected on ultrasound, further evaluation, including biopsy, may be necessary to determine the underlying cause and ensure timely treatment.