Comparison between macroscopic and full-scale microscopic appearance of the left superior horizontal bronchiole. (A) A small bronchus was dilated and the lumen surrounded by fibrosis. (B) The localization of the BO lesions with airway luminal narrowing was mainly observed in a membranous bronchiole corresponding to macroscopic appearance of a whitish small nodule. (C) The membranous bronchiolar lumen was completely obliterated. (D) The more distal bronchiole than the membranous bronchiole was dilated. (arrows) (Scale bar = 1 mm) (Elastic van Gieson stain).