Regular and irregular dichotomies of bronchial branching in the human lung

Typical models of the human bronchial tree depict regular branching. However, some anatomic studies also have revealed irregular dichotomies in the human lung. We therefore studied the patterns of bronchial branching in the human lung.

We examined a normal right lung. Bronchial branchings were traced up to terminal bronchioles (TBs) in both regular and irregular dichotomies.

In 256 TBs in peripheral regions, the number of branchings varied from 11 to 23; the largest number was found in the S10c of the basal segment, and the average was 15. In 354 TBs in hilar regions supplied by irregular dichotomies, the number of branchings ranged from 9 to 15, with the average being 10. In secondary pulmonary lobules, bronchioles supplying the secondary pulmonary lobules reached TBs in two or three divisions.

Irregular dichotomies are too frequent to be neglected in the interpretation of radiologic and physiologic findings.