Cortical thickening of a lymph node is a common finding, often identified during imaging tests like ultrasound. It simply indicates that immune cells within the node are actively multiplying and responding to a perceived threat or stimulus. While this reaction is generally a sign of a healthy and functioning immune system, the context of the finding is paramount. Only a healthcare professional can assess the specific characteristics of the thickening and determine if further medical investigation is warranted.
Understanding Lymph Node Structure and Function
Lymph nodes are small, bean-shaped organs distributed throughout the body that filter the fluid known as lymph. They are a fundamental component of the adaptive immune system, trapping and eliminating foreign invaders like bacteria, viruses, or abnormal cells. Lymph nodes are organized into the outer cortex and the inner medulla.
The cortex is the primary site where immune cells, specifically B-lymphocytes and T-lymphocytes, are concentrated. Cortical thickening occurs when these immune cells rapidly multiply in response to an infection or inflammation. This cellular expansion causes the outer layer of the node to visibly increase in size, which is then detected during imaging.
Cortical Thickening as a Reactive Process
The most frequent cause of lymph node cortical thickening is reactive hyperplasia, a benign condition. This process is the body’s adaptive response to a localized infection or inflammation in the area the node drains. The thickening shows the immune system is working effectively to contain a threat.
Common triggers for this normal immune activation include recent viral or bacterial infections, such as a sore throat, ear infection, or dental abscess. Inflammation from a localized skin irritation, a minor injury, or a recent vaccination can also cause regional lymph nodes to become reactive. In these benign cases, the node is typically mobile and may feel tender or painful to the touch, and the enlargement is expected to resolve spontaneously within a few weeks.
A normal, non-reactive lymph node cortex is typically less than 3 millimeters thick. A measurement above this threshold constitutes thickening.
When Thickening Requires Further Investigation
While most cortical thickening is benign, certain features prompt further diagnostic steps. A primary concern is persistence; a node that remains enlarged for more than four to six weeks becomes suspicious. Malignant nodes tend to be firm or hard, non-tender, and may feel fixed or matted together rather than freely movable.
Concerning imaging features include focal or eccentric thickening of the cortex, where the enlargement is uneven around the node. The loss of the central fatty hilum, which normally appears as a bright, central area on ultrasound, is a significant red flag suggesting the node’s architecture has been replaced by abnormal tissue. Systemic symptoms accompanying the thickening, such as unexplained weight loss, drenching night sweats, or a persistent fever (known as “B symptoms”), can suggest a more serious underlying condition like lymphoma or metastatic cancer.
Diagnostic Tools for Determining the Cause
Evaluation of cortical thickening typically begins with high-resolution ultrasound, which is the primary tool for characterizing the node’s internal structure. Ultrasound assesses the node’s size, shape, and the distribution of the thickening. A benign node usually maintains an oval or bean-like shape with a preserved fatty hilum, while a malignant node is often rounder and may show loss of this central hilum.
Doppler ultrasound analyzes the blood flow pattern within the node. Benign, reactive nodes typically show blood flow concentrated in the hilum, while suspicious nodes may show chaotic, increased, or peripherally distributed flow in the cortex. If imaging results or clinical presentation remain concerning, the next definitive step is obtaining a tissue sample.
Tissue sampling may involve a fine-needle aspiration (FNA) to collect a small number of cells. Alternatively, an excisional biopsy involves surgically removing the entire node for the most accurate pathological diagnosis.