CT-Pathology Correlation in Diffuse Pulmonary Diseases

1. Centrilobular diseases (1) Pulmonary emphysema Early centrilobular emphysema starts from the proximal portion of the pulmonary acinus where respiratory bronchioles and neighboring alveoli are distributed. Typical CT findings are low-attenuation areas (LAA) surrounded by perilobular normal lung. Such LAA lacks a distinct wall. Pulmonary arteries within LAA are isolated and narrowed. The disease is more prevalent in upper lobe than in lower lobe. (2) Pulmonary tuberculosis Pulmonary tuberculosis forms highly contrasting consolidation and nodules. The centrilobular tuberculous nodule is made, simultaneously involving the terminal and respiratory bronchioles at its center and adjacent alveoli. The nodule grows up to 2 mm in diameter, exceeding the size of the respiratory bronchiole, whose diameter is about 0.5 mm. Furthermore, ultra-fine branched nodules (tree-in-bud appearance) are produced frequently in pulmonary tuberculosis where the lumens of bronchioles, alveolar ducts and sacks are filled with compact caseous materials. This pathologic change is more specific than centrilobular nodules for the differential diagnosis of pulmonary tuberculosis. Other well-known diseases producing centrilobular nodules are bacterial bronchopneumonia, diffuse panbronchiolitis (DPB), pneumoconiosis, Langerhans cell histiocytosis and hypersensitivity pneumonitis (HP).