Bronchial Branching Abnormalities and Emphysema‐like Changes in Mutant Rats Having Congenital Lobation Anomalies in the Lung

ABSTRACT The present study aimed at investigating in fpl/fpl mutant rats survived to adulthood 1) whether bronchial branching abnormalities were the primary defects of pulmonary lobation anomalies, and if this was the case, 2) whether these anomalies could lead to respiratory dysfunction. Examination of corrosion casts made from the malformed lungs of adult fpl/fpl rats revealed a variety of branching abnormalities in the right bronchial tree, such as ventral ramification of the middle lobar bronchus, abnormal curvature of the intermediate lobar bronchus, and positional abnormalities of the middle lobar bronchus and first segmental bronchus of the intermediate lobar bronchus, while reduction in the number of segmental bronchi was the only minor abnormality found in the left lung. These results conformed to our previous observations in which the main manifestation of the fpl mutation was restricted to the right lung lobes, and indicated that the primary defect of this malformation was bronchial branching abnormalities. In these rats, stenosis of the trachea, right and left principal bronchi, and some lobar and segmental bronchi also became evident by calipering their circumference. Histopathological examination of the lungs revealed abnormally expanded airspaces accompanied by destruction of alveolar walls and macrophage infiltration in aged fpl/fpl rats. These observations suggest that fpl/fpl rats suffer emphysema‐like respiratory dysfunction with advancing age from pulmonary lobation anomalies conforming to tracheal and bronchial malformations.