Causes of Axillary Lymphadenopathy
Axillary lymphadenopathy is most commonly benign, but when malignancy is present, breast cancer is the leading cause, followed by lymphoma and other metastatic diseases. 1
Benign Causes
Infectious and Inflammatory Processes
- Reactive lymphadenopathy from infections is the most common benign etiology 1
- Tuberculosis can present as unilateral axillary lymphadenopathy, particularly in patients with latent TB or immunosuppression 2
- Vaccine-associated lymphadenopathy, especially after COVID-19 vaccination, occurs in 0.3-53% of vaccinated individuals and can persist for more than 100 days 3
- Acute infections causing reactive changes 4
Autoimmune and Systemic Diseases
- Rheumatoid arthritis and other collagen vascular diseases 1, 5
- Sarcoidosis 5
- Dermatopathic lymphadenopathy from skin conditions 6
- Amyloidosis 4
Breast Implant-Related
- Silicone adenitis from ruptured breast implants, where free silicone migrates to axillary lymph nodes and produces a characteristic "snowstorm" appearance on ultrasound 1
- Benign lymphadenopathy associated with intact breast implants 1
Other Benign Causes
- Nonspecific benign lymphadenopathy (most frequent benign diagnosis at 29% in screening populations) 5
- Healed granulomatous disease 4
Malignant Causes
Breast Cancer
- Metastatic breast cancer is the most common malignant cause when cancer is identified in axillary nodes 1
- Accounts for 26% of axillary lymphadenopathy cases in screening populations 5
- Can present as occult breast cancer with axillary metastases but no detectable breast primary (T0 N1b presentation), occurring in less than 1% of breast cancers 1, 7
- In patients with isolated axillary masses and confirmed cancer, occult breast cancer was found in 9 of 17 cases, with 5 in the contralateral breast 1
Hematologic Malignancies
- Chronic lymphocytic leukemia or well-differentiated lymphocytic lymphoma (17% of lymphadenopathy cases) 5
- Non-Hodgkin's lymphoma (found in 6 of 15 recalled screening patients with isolated lymphadenopathy) 4
- Other lymphomas 1
- Leukemia 4
Metastatic Disease from Non-Breast Primaries
- Metastatic carcinoma from unknown primary sites 4, 5
- Metastatic disease from known non-breast primary tumors 5
Clinical Context and Risk Stratification
Imaging Characteristics Associated with Malignancy
- Lymph node length >33 mm (specificity 97%, sensitivity 31% for malignancy) 5
- Ill-defined or spiculated margins 5
- Replacement of fatty hilum 4
- Rounded shape rather than oval 4
- Intranodal microcalcifications 5
High-Risk Scenarios
- When axillary lymphadenopathy is detected with an additional mammographic abnormality, 75% show malignancy 4
- In screening-detected isolated lymphadenopathy without known underlying cause, 52-62% have underlying malignancy 4
Important Caveats
- Most benign and malignant lymph nodes cannot be distinguished mammographically, despite statistical associations 5
- The differential diagnosis varies significantly based on whether lymphadenopathy is unilateral versus bilateral 1
- Bilateral axillary lymphadenopathy more commonly suggests systemic processes including infections, inflammatory conditions, or hematologic malignancies 1