Anatomy of Pulmonary Lymphatics and Lymphoid Tissues.

This review summarizes the 3 components of the pulmonary lymphatic system: lymphatic channels, bronchus-associated lymphoid tissue (BALT), and intrapulmonary lymph nodes. Lymphatic vessels are distributed within the bronchovascular bundles, in the interlobular septa and visceral pleura, and around small pulmonary arteries and veins within the secondary pulmonary lobules. Normally invisible on CT, they may appear with lymphatic dilation or disease spreading via lymphatic routes. BALT is usually absent histologically in healthy lungs but may be visible in smokers or autoimmune conditions. Intrapulmonary lymph nodes present as well-defined peripheral nodules in the lower lobes, often with linear opacities.