Congenital malformations of the semilunar valves

Normal semilunar valves develop at the downstream end of the embryonic cardiac tube by remodeling of the endocardial cushion material. Two valves, each with three commissures, form by subdivision of the two larger (lateral) of the four endocardial cushions. In this study congenitally malformed semilunar valves from autopsy heart specimens were reviewed to determine whether the lesions could be explained as deviations of normal valvulogenesis. The morphological spectrum of raphes and their occasional occurrence at the site of separation between the two lateral cushions, an obligatory commissure, suggested that they are usually the result of fusion of previously formed commissures. In 306 hearts there were 316 malformed semilunar valves: 208 pulmonic and 108 aortic. Four categories of lesions were found: (1) 27 atretic valves could not be interpreted; (2) 6 valves were quadricuspid with an extra commissure; (3) 45 valves showed failure of formation of one (44) or two (1) commissures; and (4) 238 valves showed fusion of one (156), two (22), or three (60) commissures as indicated by the presence of raphes. In 27 instances an atretic valve was too small to evaluate. Thus, evidence that three leaflets had at one time been present, as determined by the count of commissures plus raphes, was found in 82 per cent of interpretable valves. Several associated congenital cardiac lesions (coarctation of the aorta, transposition of the great vessels, tetralogy of Fallot, mitral atresia) exhibited a highly significant association with either aortic or pulmonic valvular malformations. The findings suggest that the majority of congenital malformations of the semilunar valves are due to lesions acquired in utero subsequent to normal valvulogenesis. Disproportionate flow reduction of the right or left side of the heart may be a factor in the development of malformations in the respective semilunar valve.