Aortic wall lamellar structure in phylogeny and in humans: insights from bicuspid and tricuspid aortic valve morphology

Objective: Despite a voluminous literature on aortopathy, comparatively little attention has been paid to the lamellar architecture of the aortic wall, including the number and distribution of these layers. This study compares the lamellar organization of the developing aorta in individuals with a bicuspid (BAV) versus tricuspid aortic valve (TAV) and includes a literature review on aortic lamellae in mammals and adult humans. Methods: Non-dilated ascending aortic wall samples (n = 83) were analyzed from individuals aged embryonic to 72 years, categorized into six age groups. Additionally, a literature review was carried out on lamellar counts across species. Results: The elastic lamellae in preterm aortas were well-structured with no pathological features. Conversely, adult aortas showed progressive elastic fiber pathology. The number of lamellae increased with age; neonates had the lowest count, peaking in young children, and gradually decreasing in adolescents. Furthermore, compared to TAV patients, BAV patients showed patterns of thinner intimal layers and fewer elastic lamellae. Our literature review showed that the quantity of lamellae in mammals is correlated with both body size and aortic radius, with smaller animals having fewer lamellae. The ascending thoracic aorta in humans had between 45 and 78 elastic lamellae, while the descending and abdominal aortas had fewer layers. Conclusion: The number of elastic lamellae in the aortic wall is influenced by both age and valve morphology. BAV patients had less lamellae than TAV patients, which could contribute to the disparity in clinical outcomes. In older adults, age-related lamellar degeneration likely increases the risk of aortopathy.