Novel patterns for the growing main bronchi in the human fetus: an anatomical, digital and statistical study

Abstract

Purpose: Intensive progress in prenatal medicine results in performing airway management in the fetus affected by life-threatening congenital malformations. This study aimed to examine age-specific reference intervals and growth dynamics for length, proximal and distal external transverse diameters, and projection surface areas of the two main bronchi at varying gestational ages, including their relative growth in length and projection surface area.

Materials and methods: Using anatomical dissection, digital image analysis and statistics, length, proximal and distal external transverse diameters, and projection surface areas of the right and left main bronchi were examined in 73 human fetuses (39 males, 34 females) aged 14-25 weeks, derived from spontaneous abortions and stillbirths.

Results: Statistical analysis showed no sex differences. Between the 14 and 25th week of gestation, the lengths of the right and left main bronchi increased from 1.43 ± 0.18 to 3.18 ± 0.39 mm, and from 2.97 ± 0.16 to 7.58 ± 1.95 mm, in accordance with the functions: [Formula: see text], respectively. The proximal external transverse diameters of the right and left main bronchi varied from 2.13 ± 0.41 to 4.24 ± 0.20 mm, and from 1.84 ± 0.06 to 3.67 ± 0.66 mm, following the logarithmic models: [Formula: see text], respectively. The distal external transverse diameter rose from 2.09 ± 0.47 to 4.24 ± 0.20 mm, as [Formula: see text] for the right main bronchus, and from 1.85 ± 0.04 to 3.67 ± 0.66 mm, like [Formula: see text] for the left one. On either side, there were no statistically significant differences between values of the proximal and distal transverse diameters of the main bronchus. The projection surface areas of the right and left main bronchi ranged from 2.95 ± 0.19 to 13.34 ± 2.12 mm(2), and from 5.57 ± 0.21 to 28.52 ± 5.24 mm(2), as [Formula: see text] and [Formula: see text]. The two main bronchi revealed a proportionate increase in both length and projection surface area, since the right-to-left bronchial length ratio and the right-to-left bronchial projection surface area ratio were stable, 0.41 ± 0.07 and 0.47 ± 0.08, respectively, throughout the analyzed period.

Conclusions: The main bronchi show no sex differences. The right and left main bronchi grow logarithmically in length and external transverse diameter, and linearly in projection surface area. The right and left main bronchi evolve proportionately, with the right-to-left bronchial ratios of 0.41 ± 0.07 for length, and 0.47 ± 0.08 for projection surface area.

Fig. 1

Measurements of the right and left main bronchi in situ in a male fetus aged 19 weeks: A trachea, B right main bronchus, C left main bronchus, 1 length of right main bronchus, 2 length of left main bronchus, 3 proximal external diameter of right main bronchus, 4 proximal external diameter of left main bronchus, 5 distal external diameter of right main bronchus, 6 distal external diameter of left main bronchus, 7 projection surface area of right main bronchus, 8 projection surface area of left main bronchus

Fig. 2

Growth dynamics of the lengths of the right (a) and left (b) main bronchi versus gestational age in human fetuses

Fig. 3

The lengths of the right and left main bronchi in human fetuses

Fig. 4

Right-to-left bronchial length ratio versus gestational age in human fetuses

Fig. 5

Growth dynamics of the proximal external transverse diameters of the right (a) and left (b) main bronchi versus gestational age in human fetuses

Fig. 6

Growth dynamics of the distal external transverse diameters of the right (a) and left (b) main bronchi versus gestational age in human fetuses

Fig. 7

Growth dynamics of the projection surface area of the right (a) and left (b) main bronchi versus gestational age in human fetuses

Fig. 8

Right-to-left bronchial projection surface area ratio versus gestational age in human fetuses