Volumetric Morphology of Segmental Trachea Sections

Abstract

Introduction & Objective The trachea is the airway between the larynx and primary bronchi, extending from the inferior aspect of the cricoid cartilage to its bifurcation at the carina. Its anterior and lateral walls are comprised of 16-22 C-shaped cartilaginous rings held together by annular ligaments, while its posterior wall consists primarily of trachealis muscle. Studies of trachea length, coronal and sagittal diameters, and dynamics are well represented in the literature with significant differences reported between genders. However, studies regarding volumetric morphology of the trachea are limited. Several structures (e.g., thyroid gland, brachiocephalic trunk, left brachiocephalic vein, etc.) are in contact with different regions of the trachea and could potentially affect lumen volumes. The objective of this study was to investigate tracheal volumetric morphology through segmental area analysis of cadaveric male and female tracheas and compare those results to a known case of distal trachea constriction. Materials & Methods Tracheas of seven male and seven female human cadavers were dissected, eviscerated, and photographed (iPad Pro, Apple Inc.). Trachea lengths were recorded to the nearest millimeter via gross measurement. Tracheas were covered at the proximal end and filled with water. Water volumes were subsequently measured in triplicate. Tracheas were then sectioned into ten equal segments and photographed (iPad Pro, Apple Inc.). Lumen areas of each segment were measured in triplicate (ImageJ, 1.52q), and mean segmental areas were multiplied by trachea length to determine segmentally derived trachea volumes. T-tests were used to compare segmentally derived volumes to actual volumes measured by water displacement. Male and female data were compared separately, and comparable data from a separate clinical case of distal tracheal constriction in a female cadaver was compared to the female data collected in this study. Results Male tracheas were longer (11.9 ± 0.7 cm vs. 10.3 ± 0.7 cm, p < 0.05) and of greater volume (28.7 ± 5.0 mL vs. 16.5 ± 0.8 mL, p < 0.05) compared to female tracheas. While sequential comparison of segmentally derived volumes in both genders suggest similar regions of natural trachea constriction (middle third) and dilation (distal third), both regions were statistically indifferent from actual trachea volume. The segmentally derived volumes from the distal half of the clinically constricted trachea were considerably less than the female volumetric data (distal half) quantified in this study (8.82 ± 1.36 mL vs. 14.86 ± 0.90 mL, p < 0.05). Conclusions & Significance While variations in lumen area of sequential trachea segments are apparent, they have little to no significant effect on total trachea volume unless substantially impacted by a clinical condition. Certain segments of the trachea may be more accurate for estimating its total volume. The noted mid-section constriction is believed to be caused by the brachiocephalic artery and left brachiocephalic vein crossing obliquely over the anterior aspect of trachea but merits more study. This study and future data expansion via additional tracheal measurements will help define “normal” tracheal volumetric morphology. This information may be valuable to physicians performing surgical procedures and diagnosing abnormalities of the trachea.