21 Congenital Absence of Aortic Valve Leaflets
Anatomy and Anatomical Associations
Congenital absence of the aortic valve leaflets is an extremely rare anomaly, with perhaps no more than two dozen reports in the literature.1–4 Absence, or dysplasia, of the pulmonic leaflets is much more common and is seen with tetralogy of Fallot. In most instances of absent aortic valve leaflets, the only remnant of the aortic valve is a nonobstructive fibrous ridge.3
Absence of the aortic valve leaflets is typically not an isolated lesion. It is associated with conotruncal anomalies, ventricular septal defect, hypoplasia of the left ventricle, and dysplasia or aplasia of leaflets of the other semilunar, the pulmonic valve.5 Absence of the aortic valve leaflets was first described in association with double-outlet right ventricle in a pathology specimen.1 In a review of 15 cases of this anomaly, hypoplasia of the left heart was seen in 11 (73%), double-outlet right ventricle in 5 (33%), and aortic arch malformations in 6 (40%).4
Frequency, Genetics, and Development
Absence of the aortic valve leaflets is extremely rare. It is commonly associated with cystic hygroma, which may offer clues to the origin of this rare anomaly.4 The relatively frequent association between absence of both the aortic and the semilunar valve leaflets has led some investigators to conclude that aplasia of the semilunar valve leaflets reflects an underdevelopment of the endocardial cushion swellings at the ventriculoarterial junction, rather than resulting primarily from an abnormality of septation of the outflow tracts.6
In one report, all seven cases were male, which suggests an X-linked process.3 DiGeorge’s syndrome has been reported in one case.4
Prenatal Physiology
Absence of a competent aortic valve results in severe aortic insufficiency. Severe aortic insufficiency affects the fetal circulation in a number of ways. In diastole, blood regurgitates back into the ventricle, which leads to a “steal” of blood flow away from the body organs and tissues. The heart dilates due to the volume load. Cardiomegaly and ventricular dysfunction ensue. Heart failure and fetal hydrops are common.5,7 Placental insufficiency can occur as blood is diverted away during diastole. Survival under such conditions is unusual. Most fetuses with this anomaly succumb with fetal demise early in the first weeks of gestation, which may explain the rare nature of the anomaly.
