Embryological evidence for the formation of a quadricuspid aortic valve in the Syrian hamster.

Congenital quadricuspid aortic valve is a rare anomaly, the morphogenesis of which remains unclear. In this study we report the case of a Syrian hamster embryo that presented an aortic valve with four valve cushions instead of three. The embryo, aged 12 days and 2 hours postcoitum, was at an early stage of valvulogenesis. It was examined using semithin sections of the heart. Two of the four valve cushions were located, one in the dorsal and the other in the left-ventral position, corresponding, respectively, to the dorsal and left valve cushions of a normal aortic valve. The remaining two cushions were situated in the right-ventral position. They were joined at the level of their basal portions and were less developed in size than the other cushions. This report seems to be the first embryological evidence for the formation of a quadricuspid aortic valve. The present findings strongly suggest that the anomalous valve originated from three mesenchymal anlagen and that the supernumerary valve cushion resulted from the division of the anlagen that normally gives rise to the right valve cushion.