Histopathological bronchial reconstruction of human bronchiolitis obliterans

To clarify the morphological mechanisms of airway obliteration in bronchiolitis obliterans (BO) associated with various causes, we conducted a retrospective study of 9 patients with a histological diagnosis of BO. The morphological characteristics were analyzed by histopathological bronchial reconstruction. BO was classified into two major morphologic subtypes: constrictive BO (CoB) and cellular/destructive BO (CDB). CoB is characterized by concentric narrowing of the airway lumen due to submucosal fibrosis. In contrast, in CDB the narrowing of the airway lumen is due to intraluminal, mural, and peribronchiolar infiltration of inflammatory cells as well as proliferation of granulation tissue. The histopathological diagnosis was CoB in 6 patients and CDB in 3 patients. Macroscopic bronchial reconstruction in CoB demonstrated that the beginnings of bronchial obliterations were in the 4th to 7th branches, numbering from each segmental bronchus and the lesions were distributed intermittently. Histopathologically, the localization of obliteration was mainly from small bronchi to membranous bronchioli with intermittent airway luminal obliteration in CoB, whereas the primary lesions in CDB revealed more continuous obliteration of the bronchiolar lumen than observed in CoB. In conclusion, this bronchial reconstruction study demonstrated marked morphological differences in the mechanisms of airway obliteration between two major morphologic subtypes of BO.