Mathematical morphologic analysis of the aortic medial structure. Biomechanical implications.

The architecture of the aortic tunica media was studied in 55 autopsy specimens (26 normotensive and 29 hypertensive patients). The purpose of the study was to elucidate whether, as commonly stated, homogeneous disposition of concentric lamellar units could be substantiated or whether an architectural gradient reflecting the decreasing biomechanical gradient in the circumferential stress, concentrated towards the inner wall, was present. The elastin lamellae thickness, interlamellar distance, fibrosis index and fragmentation index were quantitated by mathematical morphology methods. The results did not support classic histologic descriptions but showed that lamellar units were significantly thicker in the inner than in the outer zones of the media--i.e., a morphologic gradient was present. The differences between inner and outer zones were more marked in hypertensive patients than in controls. The fibrosis index increased with age, especially in hypertensive patients. The fragmentation index in hypertensive patients was significantly higher than in controls and more marked in abdominal than in thoracic aorta. This weakening in the biomechanical resistance of elastin fibers could be one of the factors explaining the predominance of aneurysms in the abdominal aorta.