The phrase “fatty hilum in a lymph node” frequently appears in medical imaging reports, such as those from ultrasound or computed tomography (CT) scans. This description refers to a specific anatomical feature visible on imaging that provides information about the node’s health. The presence of a fatty hilum is considered a reassuring finding, suggesting the lymph node is either normal or has reacted to a non-cancerous cause, like infection or inflammation. Interpreting this feature requires understanding the lymph node’s structure and function.
The Role of Lymph Nodes in the Body
Lymph nodes are small, bean-shaped organs that form a fundamental part of the lymphatic system, acting as specialized centers for immune surveillance. These structures are distributed throughout the body, clustering in areas like the neck, armpits, and groin. They function as filters for the lymph fluid, which circulates tissues collecting waste, foreign particles, and immune cells.
As the lymph fluid passes through the node, resident immune cells, including B and T lymphocytes and macrophages, trap and neutralize pathogens. This filtration process prevents the spread of infection and disease. When the body encounters a threat, immune cells within the nodes multiply rapidly, causing the node to temporarily enlarge, a condition known as lymphadenopathy.
Defining the Lymph Node Hilum
The lymph node hilum is the distinct, concave indentation on the surface of the bean-shaped organ. This area is where the body’s vascular and lymphatic systems connect to the node’s internal structure. The hilum serves as the exit point for the efferent lymphatic vessel, which carries filtered lymph fluid away from the node.
The hilum is also the entry and exit point for the node’s blood supply, including an artery and a vein. It effectively divides the node into an outer cortex and an inner medulla. On imaging, this central area often appears bright or “echogenic” on ultrasound because of the presence of supportive tissue and fat.
The Clinical Meaning of a Fatty Hilum
The presence of a well-defined fatty hilum is one of the most reliable radiological signs indicating that a lymph node is benign (non-cancerous). Adipose tissue naturally infiltrates the hilum as part of the node’s normal aging process or following resolved immune activation. On imaging, this fat creates a characteristic bright, central stripe or core that is continuous with the surrounding fat.
This preserved fatty core signifies that the internal architecture of the lymph node is intact and undisturbed. Benign or reactive lymph nodes typically maintain an oval or elongated shape, with the fatty hilum occupying the central portion. A preserved, bright fatty hilum is the primary differentiating feature for a benign node on ultrasound or CT scans.
The fatty hilum is often associated with reactive lymph nodes, which are temporarily enlarged due to infection or localized inflammation. The node is performing its normal function of fighting off a benign threat while maintaining its internal structure. However, this finding should not be interpreted in isolation, as other imaging features and the patient’s clinical history are also considered.
Features Indicating Lymph Node Abnormality
When a lymph node is infiltrated by malignant cells, the cancer disrupts the node’s normal organization, often leading to the obliteration of the fatty hilum. The loss or thinning of this central echogenic structure is a strong indicator of potential pathology, such as metastatic cancer or lymphoma. This occurs because cancerous cells multiply within the node, causing the outer layer (cortex) to thicken and compress the central fatty tissue.
Instead of the oval or bean shape, a suspicious node often adopts a more rounded, spherical appearance. Radiologists also look for irregular cortical thickening that is unevenly distributed around the hilum, or an altered pattern of blood flow detected using Doppler ultrasound. Other concerning features include a heterogeneous texture, ill-defined margins, or signs of internal necrosis, which contrast with the smooth, uniform appearance of a node with a healthy fatty hilum.