Imaging of Diseases Involving Pulmonary Lymphatics: Focus on Pulmonary Sarcoidosis

Sarcoidosis is a systemic granulomatous disorder of unknown cause, histopathologically characterized by the presence of non-caseating epithelioid-cell granulomas involving multiple organs, and most commonly involves the lungs and mediastinal and bilateral hilar lymph nodes (and the lymphatic systems). Although a definitive diagnosis relies on clinical and histopathological analysis, imaging plays a crucial role in early detection, lesion characterization, disease staging, and treatment response. This review focuses on imaging of pulmonary sarcoidosis, including histopathology, chest radiographic staging, and CT of mediastinal/hilar lymphadenopathy and parenchymal abnormalities (perilymphatic nodules, ground-glass opacity, coalescent or aggregate nodules, parenchymal fibrotic changes, and airway lesions), in addition to pulmonary hypertension and cardiac sarcoidosis. Differential diagnosis for imaging of diseases involving pulmonary lymphatics, particularly lymphangitic spread of carcinoma, is also demonstrated.