 Introduction/Background Unilateral or bilateral palpable or clinically suspicious axillary mass(es) have a broad differential diagnosis, including inflammatory, infectious, vascular, and malignant etiologies [1]. In most cases, an axillary mass confirmed on imaging is either normal tissue or of lymphoid or mammary origin. With the increased use of ultrasound (US) as a screening tool and as more advanced cross-sectional imaging detects incidental nonpalpable and clinically occult axillary findings, further evaluation with biopsy is often necessary to obtain a definitive diagnosis. The clinically negative axilla is defined having no palpable nodes on physical examination [6]. If the clinical physical examination or imaging test(s) reveal a suspicious finding, then further investigation may involve US and breast MRI. If positive, percutaneous biopsy is often performed. The National Comprehensive Cancer Network (NCCN) guidelines do refer to the use of axillary US or MRI with possible biopsy to determine if there is ipsilateral axillary lymph node involvement in operable breast cancer patients prior to preoperative systemic therapy [7]. Several imaging modalities (mammography, tomosynthesis, US, CT, fluorine-18-2-fluoro-2-deoxy-D-glucose [FDG]-PET/CT, MRI) can visualize the axillary nodes and evaluate the size and morphology. In 2014, the American Society of Breast Surgeons published a consensus guideline on the management of the axilla in which SLNB has replaced ALND for clinically node-negative invasive breast cancer patients [6]. It is desirable to identify those patients who can safely receive SLNB and those who we can potentially omit SLNB. However, there is no standard radiologic imaging test for this purpose. aThe University of Texas MD Anderson Cancer Center, Houston, Texas. bPanel Chair, Boston University School of Medicine, Boston, Massachusetts. cPanel Vice-Chair, New York University School of Medicine, New York, New York.
Imaging of the Axilla.  Introduction/Background Unilateral or bilateral palpable or clinically suspicious axillary mass(es) have a broad differential diagnosis, including inflammatory, infectious, vascular, and malignant etiologies [1]. In most cases, an axillary mass confirmed on imaging is either normal tissue or of lymphoid or mammary origin. With the increased use of ultrasound (US) as a screening tool and as more advanced cross-sectional imaging detects incidental nonpalpable and clinically occult axillary findings, further evaluation with biopsy is often necessary to obtain a definitive diagnosis. The clinically negative axilla is defined having no palpable nodes on physical examination [6]. If the clinical physical examination or imaging test(s) reveal a suspicious finding, then further investigation may involve US and breast MRI. If positive, percutaneous biopsy is often performed. The National Comprehensive Cancer Network (NCCN) guidelines do refer to the use of axillary US or MRI with possible biopsy to determine if there is ipsilateral axillary lymph node involvement in operable breast cancer patients prior to preoperative systemic therapy [7]. Several imaging modalities (mammography, tomosynthesis, US, CT, fluorine-18-2-fluoro-2-deoxy-D-glucose [FDG]-PET/CT, MRI) can visualize the axillary nodes and evaluate the size and morphology. In 2014, the American Society of Breast Surgeons published a consensus guideline on the management of the axilla in which SLNB has replaced ALND for clinically node-negative invasive breast cancer patients [6]. It is desirable to identify those patients who can safely receive SLNB and those who we can potentially omit SLNB. However, there is no standard radiologic imaging test for this purpose. aThe University of Texas MD Anderson Cancer Center, Houston, Texas. bPanel Chair, Boston University School of Medicine, Boston, Massachusetts. cPanel Vice-Chair, New York University School of Medicine, New York, New York.