Causes of Axillary Adenopathy with FDG Uptake on PET-CT

Malignant Causes

Metastatic breast cancer is the most common malignant cause of axillary adenopathy with FDG uptake, though less than 1% of breast cancers initially present as isolated axillary adenopathy 4, 5
FDG-PET/CT demonstrates high specificity (90-100%) but variable sensitivity (48-87%) for detecting axillary lymph node metastases from breast cancer 6
Lymphoma and leukemia are the most common non-mammary malignancies causing bilateral axillary adenopathy with FDG uptake 2, 3, 5
Other non-mammary malignancies can metastasize to axillary nodes, though this is less common 1, 2

Benign reactive lymphadenopathy from infectious and inflammatory processes is a common cause of FDG-avid axillary nodes 2, 3, 5
Infectious etiologies include mastitis, granulomas, and skin wound infections 1, 7
Autoimmune diseases can also cause reactive axillary adenopathy with FDG uptake 8

Axillary ultrasound is the primary modality of choice for initial evaluation, as it can determine if nodes are solid or cystic and assess morphologic features 7
Ultrasound-guided biopsy should be performed for suspicious nodes, providing definitive diagnosis with high specificity (98-100%) 7
Diagnostic mammography and/or digital breast tomosynthesis should complement axillary ultrasound to evaluate for potential breast primary lesions 7
If occult breast cancer is suspected with negative mammography, breast MRI can identify the primary lesion in approximately 70% of cases 7

FDG uptake by an axillary node does not always represent true metastatic disease, as multiple benign causes exist 6
Clinical context is essential, as the majority of enlarged lymph nodes have benign reactive changes 7