Fig 1.
Image processing of the bronchial tree and definitions of the node and branch.
(A) Image acquisition and three-dimensional reconstruction were performed. (i) Serial transverse section using phase-contrast X-ray computed tomography (ID 18071). D, dorsal; L, left; R, right; V, ventral. (ii) Reconstructed bronchial tree. (iii) Transparent reconstruction and centerline tree. (B) An illustration of bifurcation indicating the definitions of node and branch in the present study. Simplified centerline indicating bifurcation. The white and black lines represent the node and branch, respectively. The proximal branch of the bifurcation was defined as the parental branch (PBr), and peripheral branches were defined as child branches (CBr).
Fig 2.
Categorization flowchart and schematic diagram indicating monopodial and dipodial branching.
(A) (i) Illustration showing the definition of NC and TC (upper), and the definitions of a, b, c, and d (lower). Here, a and b are the shortest and longest PBr(NC) lengths, respectively, and c and d are the shortest and longest PBr(TC) lengths, respectively. CBr, child branch; NC, bifurcation that generates no child branches; PBr, parent branch; TC, bifurcation that generates two child branches. (ii) Flowchart of the branching mode categorization. (B) Illustration showing the change in PBr length with dipodial and monopodial branching. The PBr length may not shrink or elongate with dipodial branching (i), but may shrink with monopodial branching (ii) just after generation of CBr. (C) Schematic graphs of PBr length subjected to bifurcation by dipodial and monopodial branching. The branching mode was categorized as dipodial or monopodial branching according to the change in the PBr length. When the PBr(TC) length remained constant with the birth of CBr, the CBr were formed with dipodial branching (i). When the PBr(TC) length was shortened with the birth of CBr, the CBr were formed with monopodial branching (ii).
Fig 3.
Branching mode of the lobar bronchi.
(A) Idealized diagram of the generation period of the lobar bronchus. No lobar bronchus existed during phase 1. The RMLB and LSLB sprouted during phase 2. During phase 3, all lobar bronchi were formed. The length changes of the right proximal bronchi (B) and the left proximal bronchi (C) are shown. Compared with the RPBB length during phase 1, the RMB length and total length of RMB and IB were shorter (B). Similarly, the LMB length was shorter than the LPBB length (C). IB, intermediate bronchus; LIB, left inferior bronchus; LMB, left main bronchus; LPBB, left primary bronchial bud; RIB, right inferior bronchus; RMB, right main bronchus; RPBB, right primary bronchial bud; temRMB, temporary RMB branch from the tracheal bifurcation to the base of the right middle lobe.
Table 1.
Categorization of the branching mode of the lobar bronchus.
Fig 4.
Branching mode categorizations of segmental and subsegmental bronchi.
The length change of each segmental or subsegmental bronchus is shown. The graph titles indicate the bifurcation. X axis is sample number and Y axis is length. The graph color reflects the categorization of the bronchus. The red graph represents dipodial branching. The blue graph represents monopodial and probable monopodial branching. The graph of the uncategorized bronchus is monochrome. In the B8(7+8)sub graph, a bordered gray bar graph describes the probable B8(7+8) length, which was classified as B8(7+8) based on the orientation in immature samples. BXsub, subsegmental bronchus of BX; LB, lingular bronchus; LSLB, left superior lobar bronchus; RILB, right inferior lobar bronchus; RMLB, right middle lobar bronchus; RSLB, right middle lobar bronchus; RSLB, right superior lobar bronchus; SDB, superior division bronchus.
Table 2.
Branching modes of segmental and subsegmental bronchi.
Fig 5.
The length of the left superior lobar bronchus did not become shorter with growth.
(A) The total length of the passage from the LSLB to the lateral peripheral bronchus. These lengths were sorted according to the generation of passage; subsequently, they were sorted in ascending order. Reconstructions of samples with numbers 1–5 are shown in (B). (B) Representative reconstructions indicated morphological changes according to growth. The LSLB length was almost constant. Scale bar: 100 μm. Ventrocranial view. BrX, branch without an identified anatomical term; D, dorsal; L, lateral; LB, lingular bronchus; LMB, left main bronchus; LSLB, left superior lobar bronchus; M, medial; NC, no child; SDB, superior division bronchus; V, ventral.