Normal Size of Intramammary Lymph Nodes
Normal intramammary lymph nodes typically measure up to 10 mm in long-axis diameter and are considered benign when they demonstrate characteristic morphological features. 1
Characteristics of Normal Intramammary Lymph Nodes
- Normal intramammary lymph nodes are well-circumscribed, oval or round structures that may be visualized on imaging studies 2, 3
- They typically demonstrate a fatty hilum, lobular or oval shape, and circumscribed margins without evidence of central necrosis, cortical thickening, or loss of fatty hilum 1
- On ultrasound, normal intramammary lymph nodes appear as well-defined echo-poor masses with echogenic centers 4
- They are most commonly located in the upper outer quadrant of the breast 2, 5
Size Parameters for Normal vs. Abnormal Intramammary Lymph Nodes
- Intramammary lymph nodes measuring up to 10 mm in long-axis diameter are commonly seen on high-risk screening breast MRI examinations in patients without breast cancer and are considered benign 1
- In patients with newly diagnosed breast cancer, the American Joint Committee on Cancer suggests a long-axis measurement of ≥ 5 mm as a guideline to differentiate benign versus potentially malignant intramammary lymph nodes 1
- Nodes that are 1 cm or larger in diameter without a lucent center or hilar notch should raise suspicion for malignancy 3
Morphological Features That May Indicate Abnormality
- Loss of fatty hilum, irregular shape, and rounded appearance (which can be quantified by a short-axis/long-axis length ratio greater than 0.5) raises suspicion for metastatic disease 1
- Metastatic intramammary lymph nodes typically appear enlarged (≥1 cm), homogeneous, and well-circumscribed without the lucent center or hilar notch characteristic of benign nodes 3
- Development of malignant microcalcifications within an intramammary lymph node may indicate metastatic involvement 2
Clinical Significance
- Intramammary lymph node involvement in breast cancer can alter clinical staging and treatment planning 1
- The American Joint Committee on Cancer recommends that positive intramammary lymph nodes should be counted as positive lymph nodes in the N staging 6
- Metastatic disease to intramammary lymph nodes may be the first clinical and/or radiographic sign of breast cancer 2, 3
Imaging Modalities for Assessment
- MRI and PET-CT demonstrate the highest sensitivities for detecting abnormal intramammary lymph nodes 1
- Ultrasound is helpful for staging, and ultrasound-guided fine-needle aspiration can be performed in cases of suspected metastasis 1
- On mammography, suspicious nodes appear as well-circumscribed, homogeneous, oval or round opacities, typically larger than 1 cm 2