[Clinical, imaging, and pathological features of diffuse alveolar filling diseases]

Diffuse alveolar filling disease (DAFD) is characterized by diffuse lesions in both lungs caused by the abnormal filling of bilateral alveolar spaces (and sometimes the terminal bronchioles) with substances such as water, blood, lipids, inflammatory cells, pathogens, or tumor cells. Clinically, it is characterized mainly by dyspnea and hypoxemia, while imaging examinations reveal diffuse ground-glass opacities or consolidation shadows in both lungs. In the early stage, lung volume generally remains unchanged, but pulmonary interstitial fibrosis may occur in the advanced stage. Typical diseases included in this category are pulmonary alveolar proteinosis (PAP), diffuse alveolar hemorrhage (DAH), idiopathic pulmonary hemosiderosis (IPH), and pneumocystis pneumonia (PCP). While these diseases share certain similarities in clinical symptoms, imaging features, and pathological manifestations, each has its own distinct characteristics. Bronchoalveolar lavage fluid (BALF) detection and lung biopsy are the main confirmatory diagnostic methods. As a newly proposed concept, DAFD and diffuse interstitial lung diseases (DILD) both belong to diffuse parenchymal lung diseases (DPLD). The formal proposal of this new concept is of great significance for the diagnosis and differential diagnosis of DPLD.