REVERSED CIRCULATION IN ACARDIAC FETUSES IS ASSOCIATED WITH ANATOMIC INVERSIONS IN THE AORTIC-WALL

Blood vessel anatomy is probably related to hemodynamic factors which change during development. This principle has been postulated as the b asis for differences in the numbers of elastic lamellae in the tunica media of the proximal and distal human aorta. Recent stud ies of human fetuses at varying stages confirmed that the number of elastin lamell ae in the aortic wall varied along its length (spatially) and with age (temporally). These findings suggest that hemodynamic influences duri ng prenatal development induce structural changes in the aortic wall. Acardiac fetuses provide a model for studying the effects of hemodynam ic changes on the structure of elastic arteries because blood flow thr ough the aorta in such fetuses is reversed and greatly reduced. Also, analysis of the vascular structure of acardiac fetuses would further d efine the characteristic features of this congenital disorder. In the present study, we have examined the gross and histological anatomy of the aorta from seven acardiac fetuses. In each case, the microscopic a rchitecture of the aorta was deranged and the normal proximal-distal d ifferences in arterial caliber and number of elastin lamellae were rev ersed. In the proximal aorta, medial lamellar units were thin, fragmen ted, and irregular. In some segments, only traces of medial lamellar u nits existed. We believe that these anatomic abnormalities represent d egenerative or dysplastic responses to reversed flow and pressure grad ients in the aorta. These findings are consistent with the hypothesis that aortic wall structure is influenced by hemodynamic factors during development. (C) 1994 Wiley-Liss, Inc.