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Lymph Node Evaluation in Breast Imaging
Overview
This chapter provides a framework for the diagnostic approach to axillary lymphadenopathy and its differential considerations including unilateral axillary lymphadenopathy, bilateral axillary lymphadenopathy, and axillary nodal calcifications. A brief overview of the evaluation and management of axillary lymph nodes in newly diagnosed breast cancer patients concludes the chapter.
Axillary lymphadenopathy can be encountered during the evaluation of a palpable lump in the axilla, as part of locoregional staging for a highly suspicious finding or known biopsy-proven malignancy in the breast, as an incidental finding from other imaging (e.g., computed tomography [CT], magnetic resonance imaging [MRI], positron emission tomography [PET]/CT), or infrequently as an isolated finding from breast cancer screening (<0.5% screening mammography examinations). Though axillary lymph nodes may be visualized on mammography, ultrasound is the preferred imaging modality for specific evaluation of the axilla. Imaging evaluation of a palpable axillary lump starts with diagnostic mammography to evaluate for potential associated findings in the breast (sometimes with specialized views including exaggerated craniocaudal lateral and axillary tail views) followed by targeted ultrasound of the clinical area of concern. For locoregional staging in a patient with newly diagnosed breast cancer, sonographic evaluation of the entire ipsilateral axilla is performed. Suspicious findings on ultrasound can be biopsied by ultrasound-guided fine-needle aspiration (FNA) or ultrasound-guided core biopsy with marker clip placement.
Basic Anatomy
The axilla is composed of nerves, blood vessels, adipose tissue, muscles, lymph nodes, and fibroglandular tissue. It is bounded superiorly by the clavicle, scapula, and first rib; anteriorly by the pectoralis major and minor muscles; medially by the serratus anterior muscle and thoracic wall; and posteriorly by the scapularis, teres major, and latissimus dorsi muscles.
Axillary lymph nodes receive lymphatic drainage from the arm, breast, walls of the thorax, and upper walls of the abdomen. The lymphatic vessels then course through the pectoralis major muscle and enter the internal mammary lymph nodes.
Surgical levels of axillary lymph nodes are defined by their relationship to the pectoralis minor muscle. Level I nodes are located lateral to the pectoralis minor muscle. Level II nodes are located posterior to the pectoralis minor muscle and also include interpectoral nodes located between the pectoralis major and minor muscles (Rotter nodes). Level III nodes are located medial to the pectoralis minor muscle. Fig. 17.1 demonstrates examples of level I, level II, and level III axillary lymph nodes.
Normal Versus Abnormal Appearance
Normal axillary lymph nodes can vary in size from a few millimeters to several centimeters in longest dimension. The most important criterion for distinguishing between normal and abnormal lymph nodes is thus based on morphology. The following characteristics should be evaluated: size, shape (oval, round, irregular), cortical thickening (uniform/concentric, focal), margin (circumscribed, not circumscribed), and hilar compression or replacement.
Normal lymph nodes are oval in shape and have a fatty hilum, which is seen as a lucent center or notch on mammography, and an echogenic center on ultrasound. They have a thin uniform cortex (<3 mm), and Doppler evaluation shows vascularization only within the hilum. Fig. 17.2 demonstrates the normal appearance of axillary lymph nodes on mammography, ultrasound, CT, and MRI.
![Fig. 17.2, Normal appearance of axillary lymph nodes. (A) On mammogram (mediolateral oblique [MLO] view), normal lymph nodes demonstrate a thin white cortex ( arrow ) and radiolucent fatty hilum (*). (B) On ultrasound, the cortex is thin and hypoechoic ( arrows ) and the fatty hilum is isoechoic. (C) Computed tomography (CT) and (D) magnetic resonance imaging (MRI) show the normal reniform shape with smooth enhancing cortex and central fatty hilum (lymph nodes annotated by arrows).](https://storage.googleapis.com/dl.dentistrykey.com/clinical/LymphNodeEvaluationinBreastImaging/1_3s20B9780323758499000175.jpg "Fig. 17.2, Normal appearance of axillary lymph nodes. (A) On mammogram (mediolateral oblique [MLO] view), normal lymph nodes demonstrate a thin white cortex ( arrow ) and radiolucent fatty hilum (*). (B) On ultrasound, the cortex is thin and hypoechoic ( arrows ) and the fatty hilum is isoechoic. (C) Computed tomography (CT) and (D) magnetic resonance imaging (MRI) show the normal reniform shape with smooth enhancing cortex and central fatty hilum (lymph nodes annotated by arrows).")
Suspicious features include rounded shape, focal cortical bulge, eccentric cortical thickening, diffuse cortical thickening greater than 3 mm, complete or partial effacement of the fatty hilum, and nonhilar blood flow. An irregular shape and/or indistinct margin may indicate extranodal extension, a poor prognostic sign. Fig. 17.3 demonstrates the various abnormal appearance of axillary lymph nodes on ultrasound ( Box 17.1 ).
Box 17.1
Real-time ultrasound scanning is recommended for evaluating lymph node cortical thickness, since projection/positional artifacts such as an oblique angle of insonation can simulate cortical thickening.
Diagnostic Approach
A variety of benign and malignant processes can result in axillary lymphadenopathy and the loss of normal nodal morphology. Fig. 17.4 provides a framework for the diagnostic approach to breast imaging evaluation of axillary lymph nodes. Reviewing the electronic medical record and prior available imaging are important for identifying potential known causes of axillary lymphadenopathy and for assessing stability.
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