Novel insights into the elastic and muscular components of the human trachea.

Despite its probable importance in health and disease, the elastic tissue in the trachea has rarely been investigated. In addition, various aspects of the trachealis muscle are controversial. The aim of this study was to clarify this clinically relevant anatomy. Ten cadaveric tracheobronchial specimens (age range 68-101 years; seven males; no major airway pathology) were qualitatively investigated by microdissection. Serial histologic sections from multiple sites in three specimens were analyzed after staining for elastin. Findings were correlated with observations from video tracheobronchoscopies. An extensive and prominent meshwork of elastic tissue was found within the trachea and bronchi. Elastic fibers were predominantly longitudinal and aggregated into discrete bundles within the membranous wall of the trachea and main bronchi; a discrete fibroelastic membrane bridging the membranous wall of the trachea; and vertical laminae connecting the ends of successive cartilages. The longitudinal elastic bundles continued into the segmental bronchi, becoming thinner and more circumferentially distributed. Trachealis consisted of a transverse layer of smooth muscle deep to the fibroelastic membrane of the membranous wall of the trachea, together with scattered longitudinal muscle bundles, mostly embedded within the fibroelastic membrane in the distal half of the trachea. In conclusion, there is an extensive but relatively neglected elastic framework within the tracheobronchial tree. This is likely to have major clinical relevance to the pathophysiology of respiratory disease and ageing. The trachealis muscle is more complex than previously stated.