Differential distribution of lymphatic clearance between upper and lower regions of the lung

Background and objective Many lung diseases arise as the consequence of inhalational injury. When pathogenic materials are inhaled, it is possible that their clearance routes become the main focus of injury in the lung. Lymphatic clearance is important in the removal from the lung of small inhaled particles. The leak of toxic agents from the lymphatic flow potentially explains the topographic distribution of diffuse lung diseases triggered by inhaled materials, for example asbestosis. The aim of this study was to evaluate the differences in lymphatic distribution across various craniocaudal levels of the lung by using carbon dust deposition (CDD) as a tracing marker. Methods We evaluated 61 HE-stained slides of the normal lung area from 61 lobectomy specimens. The intensity of CDD was scored into five degrees (0–4) in bronchiolovascular (BV) areas and subpleural/septal (SP) areas per slide. The distribution was highlighted by subtraction scores of SP areas from those of bronchiolovascular areas. Results The subtraction scores of the upper lung area were significantly greater than those in the lower area, whereas there was no significant difference in scores by pulmonary lobes. Conclusions Our results indicated that the main lymphatic clearance routes vary according to the craniocaudal levels, and are predominant in BV areas of the upper areas and in SP areas of the lower areas of the lung. This may explain the histological variations in anatomical distribution observed in the biopsy specimens of some diffuse lung diseases.