Anatomy, variation, and asymmetry of the bronchial tree in the African grey parrot (Psittacus erithacus)

Abstract

The avian bronchial tree has a unique and elaborate architecture for the maintenance of unidirectional airflow. Gross descriptions of this bronchial arrangement have traditionally relied upon dissection and casts of the negative (air‐filled) spaces. In this study, the bronchial trees of five deceased African grey parrots (Psittacus erithacus) were segmented from micro‐computed tomography (μCT) scans into three‐dimensional (3D) surface models, and then compared. Select metrics of the primary bronchi and major secondary branches in the μCT scans of 11 specimens were taken to assess left–right asymmetry and quantify gross lung structure. Analysis of the 3D surface models demonstrates variation in the number and distribution of secondary bronchi with consistent direct connections to specific respiratory air sacs. A single model of the parabronchi further reveals indirect connections to all but two of the nine total air sacs. Statistical analysis of the metrics show significant left–right asymmetry between the primary bronchi and the origins of the first four secondary bronchi (the ventrobronchi), consistently greater mean values for all right primary bronchus length metrics, and relatively high coefficients of variation for cross‐sectional area metrics of the primary bronchi and secondary bronchi ostia. These findings suggest that the lengths of the primary bronchi distal to the ventrobronchi do not preserve lung symmetry, and that aerodynamic valving can functionally accommodate a wide range of bronchial proportions.

Humeral air sac neoplasm in a cockatiel (Nymphicus hollandicus)

“…To date, complete air sac morphology has not been detailed in the cockatiel, further research may reveal the behaviour of air sac carcinomas and define the cause of metastasis in some species but not others. Echols reports that additional research is being conducted to accurately characterize the pulmonary system of multiple avian species, which will help us better understand these anatomic variations and connections 11 . This research may help us understand air sac neoplasms and their behaviour within and between species.…”

“…Echols reports that additional research is being conducted to accurately characterize the pulmonary system of multiple avian species, which will help us better understand these anatomic variations and connections. 11 This research may help us understand air sac neoplasms and their behaviour within and between species.…”

“…1,2,6,8,9 Air sac carcinomas are found in other locations of varying avian species, including the clavicular, sternal and cervical air sacs. 1,3,6,10 Recently, air sac anatomy disparities have been described both between and within avian species, 11 which may affect the behaviour of respiratory neoplasms in birds. Large psittaciforms, specifically cockatoos, are overrepresented in current literature describing humeral air sac carcinomas, whereas cockatiels have not been described.…”

Architecture of the bronchial tree in Cuvier's dwarf caiman (Paleosuchus palpebrosus)

“…3D surface models were segmented in Avizo 7.1 and 2020.3 (Thermo Fisher Scientific) following the methods established for extant archosaur lungs (Farmer & Sanders, 2010; Lawson et al, 2021; Sanders & Farmer, 2012; Schachner et al, 2013, 2017, 2021). For a detailed description of the segmentation methodology used, see Lawson et al (2021). Bronchial tree colors in figures indicate proposed homologies and follow Schachner et al (2021).…”

“…Quantitative measurements of the airways were collected from the DICOM editor and viewer OsiriX MD (http://www.osirix-viewer.com) and are included in Table S1. These measures have been established in previous work (Lawson et al, 2021; Schachner et al, 2021), and were based upon hypothesized homologous structures in other crocodilians (Farmer, 2015b; Sanders & Farmer, 2012; Schachner et al, 2013, 2021), as well as developmental work on reptiles and birds (Broman, 1939; Locy & Larsell, 1916a, 1916b). All measures were completed in the 3D MPR viewer of OsiriX.…”