Imaging Evaluation of Mediastinal and Hilar Lymphadenopathy: Approach, Classification, and Differential Diagnosis.

Mediastinal and hilar lymphadenopathy is a frequent finding in thoracic imaging, necessitating thorough evaluation to distinguish between transient, reactive, malignant, and non-malignant causes. This review explores the anatomy, function, and drainage patterns of thoracic lymph nodes, including the International Association for the Study of Lung Cancer (IASLC) classification system, which standardizes lymph node stations for lung cancer staging and broader diagnostic applications. Imaging modalities such as chest radiography (CXR) and computed tomography (CT) play crucial roles in assessing lymphadenopathy, with CT being the preferred tool due to its ability to characterize size, shape, borders, density, and enhancement patterns. Specific imaging features, including nodal size thresholds, calcification patterns, necrosis, and distribution, help narrow differential diagnoses, distinguishing between malignant and benign conditions such as tuberculosis, sarcoidosis, lymphoma, and metastases. Additionally, the involvement of extra-mediastinal nodes can provide diagnostic clues to systemic diseases. A systematic imaging approach enhances diagnostic accuracy, guiding appropriate clinical management and tissue sampling when necessary.