Causes of Bilateral Axillary Adenopathy
Bilateral axillary adenopathy most commonly suggests systemic processes including infections, inflammatory conditions, or hematologic malignancies rather than localized disease. 1
Malignant Causes
Lymphoma and leukemia are the most common malignant causes of bilateral axillary adenopathy. 1, 2
- Non-Hodgkin's lymphoma specifically represents a primary hematologic malignancy that frequently presents with bilateral nodal involvement 3, 2
- When bilateral axillary adenopathy is detected on screening mammography with no apparent etiology, there is a remarkably high positive predictive value for malignancy—41.7% of such cases proved to be non-Hodgkin lymphoma in one series 4
- Metastatic breast cancer, while the most common malignant cause of unilateral axillary adenopathy, is less typical for bilateral presentation unless there is advanced systemic disease 1, 2
Infectious and Inflammatory Causes
Reactive lymphadenopathy from infections represents the most common benign etiology overall. 1
- Specific infectious causes include mastitis, granulomatous infections (including tuberculosis, though this more commonly presents unilaterally), and systemic viral infections 3, 2, 5
- Autoimmune diseases can produce bilateral reactive adenopathy 3, 2
- Dermatopathic lymphadenopathy from chronic skin conditions may cause bilateral involvement 1
- Kikuchi-Fujimoto disease (histiocytic necrotizing lymphadenitis) can mimic malignant lymphoma and present with bilateral axillary involvement 6
Implant-Related Causes
Silicone adenitis from ruptured breast implants produces characteristic bilateral axillary adenopathy with a "snowstorm" appearance on ultrasound. 3, 1
- This can occur with both ruptured and intact implants, as silicone migration to regional lymph nodes is the second most common site for free silicone after the breast itself 3
- Silicone adenitis can demonstrate FDG uptake on PET/CT, creating false-positive findings that mimic metastatic disease 2, 7
Iatrogenic Causes
Recent COVID-19 vaccination can cause bilateral hypermetabolic axillary lymphadenopathy, particularly when vaccines are administered in alternating arms. 8
- This represents an increasingly recognized cause of bilateral adenopathy in the post-pandemic era 8
- The pattern may be asymmetric depending on injection sites and timing 8
Critical Clinical Pitfall
Do not dismiss bilateral axillary adenopathy as simply reactive without thorough evaluation—when detected on screening mammography with no apparent cause, up to 42% represent underlying lymphoma. 4 The bilateral nature does not guarantee benignity; it shifts the differential toward systemic processes that require definitive diagnosis through ultrasound-guided biopsy rather than observation alone 3, 2.