A breast magnetic resonance imaging (MRI) scan effectively shows lymph nodes, especially in the axillary (underarm) region. This capability is valuable in the comprehensive diagnosis and staging of breast cancer. MRI’s detailed images allow medical professionals to assess node presence, size, and characteristics.
Why Axillary Lymph Nodes are Examined
The body’s lymphatic system is a complex network of vessels and organs vital for fluid balance and immune defense. Lymph nodes, small, bean-shaped structures distributed throughout this network, filter lymph fluid and house immune cells. Breast cancer cells often travel through lymphatic vessels to the nearby axillary lymph nodes first due to their proximity and direct drainage pathway. Examining these nodes is a standard and important part of breast cancer staging, indicating if cancer has spread beyond the breast. This information guides treatment and provides insights into the disease’s overall prognosis.
Visualizing Lymph Nodes with MRI
Breast MRI uses magnetic fields and radio waves to create highly detailed images of soft tissues, effectively visualizing lymph nodes. The magnetic field aligns water molecules in the body; pulsed radio waves briefly knock them out of alignment. As they realign, they release energy signals detected by the scanner and translated into precise images. A gadolinium-based contrast agent is typically administered intravenously to enhance visibility. This agent alters water molecule properties, causing areas with increased blood flow, like tumors or inflamed lymph nodes, to appear brighter on the images, improving differentiation and detail.
Interpreting MRI Lymph Node Findings
Radiologists meticulously evaluate MRI images for specific characteristics that distinguish normal from suspicious lymph nodes. Normal axillary lymph nodes are typically small, oval or bean-shaped, with a distinct fatty center, referred to as the hilum. These benign nodes generally show gradual, uniform contrast uptake.
Suspicious nodes often show several key morphological changes. These include enlargement, a rounded shape, or loss of the fatty hilum. Cortical thickening (outer rim > 2.5-3.0 mm) is also a concern. Suspicious nodes may also show rapid contrast enhancement followed by quick “washout,” reflecting altered vascularity commonly associated with malignancy. Perifocal edema (swelling in surrounding fat) can also be a strong sign of potential malignancy.
Follow-Up Procedures for Suspicious Nodes
Suspicious lymph nodes on a breast MRI do not automatically confirm cancer spread; further diagnostic steps are usually recommended. This typically involves obtaining a tissue sample for definitive pathological examination. A common method is an ultrasound-guided needle biopsy, where a radiologist uses ultrasound imaging to guide a thin needle into the suspicious lymph node to collect cells or a tissue core. The collected sample is then sent for microscopic analysis to determine if cancer cells are present.
Another procedure, often performed during breast cancer surgery, is a sentinel lymph node biopsy. This involves identifying and removing the first lymph nodes to which cancer cells would likely spread from the breast tumor, helping to accurately stage the cancer and guide subsequent treatment decisions.