Lymph Nodes
Lymph nodes on breast MRI are categorized by location (intramammary, axillary, internal mammary) and appearance (normal vs. abnormal). In BI-RADS v2025, lymph nodes were elevated from a sub-category of “associated features” to a separate lexicon category, reflecting their clinical importance.
Three Lymph Node Locations
| Location | Description |
|---|---|
| Lymph Node — Intramammary | Within the breast parenchyma; usually lateral/upper |
| Lymph Node — Axillary | Levels I, II, III relative to pectoralis minor |
| Lymph Node — Internal Mammary | Parasternal; along internal mammary vessels |
Normal Lymph Node Features (All Locations)
- Circumscribed margin
- Reniform (kidney-bean) shape
- Homogeneously enhancing
- T2 hyperintense
- Fatty hilum visible (may be absent in small nodes)
Board Pearl
Normal axillary lymph nodes can show fast early and washout delayed kinetics — this kinetic pattern is not suspicious in lymph nodes, unlike in breast masses. Do not mistake normal lymph node kinetics for malignancy.
v2025 Change
Abnormal lymph nodes were previously categorized under “associated features” as “lymphadenopathy.” BI-RADS v2025 created a separate lymph node category across modalities due to the importance of detailed lymph node description.
BI-RADS Assessment Rules for Lymph Nodes
- Ipsilateral abnormal nodes + known breast malignancy: Describe fully but do NOT give a separate BI-RADS assessment
- Isolated abnormal nodes (no ipsilateral malignancy): Give a BI-RADS assessment based on level of suspicion
- Lymph nodes with known lymphoma/CLL: BI-RADS 2
Board Pearl
The ultrasound cortical thickness threshold of >3 mm does NOT apply to breast MRI. Many normal MRI lymph nodes appear to have cortical thickness >3 mm due to partial volume averaging. Subjective asymmetry is the key criterion on MRI.