Internal Thoracic Lymphadenopathy in Breast Cancer

The internal thoracic (IT) nodal basin is a first-echelon drainage pathway in the breast, accounting for up to a quarter of its lymphatic drainage, primarily from the deep structures of the breast. The presence of internal thoracic node (ITN) metastases upstages the breast cancer (BC) patient to a minimum of clinical stage III disease. Medial tumors, deep tumors, young age, axillary nodal metastases, tumors of a high nuclear grade, lymphovascular invasion, and triple-negative hormone receptor status are predisposing factors for ITN metastases from primary BC. It has been observed that medial tumors carry a worse prognosis than lateral tumors when all other factors are equal, indicating that understaging of ITN has a significant impact on patient outcomes. Despite the established prognostic significance of IT adenopathy in BC, this nodal basin is not routinely staged due to the difficulty in accessing it and due to the controversy regarding its management. Since the initial ITN studies in the 1960s, improvement in imaging techniques and the availability of minimally invasive biopsy techniques have fueled renewed interest in ITNs and their clinical significance in BC. Radiologists who image and diagnose BC can offer more accurate staging assessments by consistently evaluating the IT nodal chain in the BC patient. In this article, the authors discuss current knowledge of the ITNs in BC and review ITN anatomy. The imaging appearance of pathologic ITNs using various modalities, potential mimics of IT adenopathy, and image-guided sampling techniques are described. A succinct discussion of the clinical management of ITN-positive BC and its challenges is also included. ^© RSNA, 2017.