Semilunar valves, the aortic and pulmonary, guard the origins of ascending aorta and pulmonary trunk arising from the left and right ventricles, respectively. These valves have three cusps (tricuspid/trileaflet) each and exhibit a semilunar margin attached to the arterial wall (hinge), a more or less straight but curved free margin with a thickening in the center (Nodule of Arantius), junction of free margins of adjacent cusps attached to the arterial wall (Commissure), and two surfaces convex facing the ventricular cavity and concave facing the arterial wall. Sinuses (of Valsalva) are depressions between the arterial wall and the concave surface of the cusps and are larger in the ascending aorta. The valve leaflets and the sinuses are similarly named. Two of the aortic sinuses give origin to coronary arteries, hence named, respectively, as the right coronary sinus and left coronary sinus, and the third noncoronary sinus is named as nonadjacent sinus, which is right posterior anatomically. The sinuses and cusps of the pulmonary trunk are smaller and named right adjacent, left adjacent, and nonadjacent leaflets. A portion of the wall of the great arteries proximal to the attached margin of the cusps and between the cusps is named the intercalated triangle. At the base of these triangles lie the transition zone between smooth muscles of arterial walls (positive for smooth muscle ∞ actin) and myocardium (negative for smooth muscle ∞ actin) of the outflow portions of the ventricles. The arterial semilunar valves have a common origin from endocardial cushions and are closely related to septation of the outflow tract (OFT), the truncus arteriosus, regulated by cardiac neural crest cells (NCC). Congenital malformations affecting the semilunar valves include variability in the number of leaflets/cusps (bicuspid, quadricuspid, and unicuspid) and size and shape (dysplastic/aplastic). Bicuspid aortic valve (BAV) is the most common congenital cardiac anomaly affecting 1%–2% of the general population. In this issue, an article by Akturk et al.1 observed a statistically significant increase in the diameter of the aorta between patients with BAV and normal age-matched patients with a tricuspid valve. Nearly 45% of BAV subjects exhibit calcific aortic valve disease requiring surgical replacement of the malformed BAV. They also suggested that the thickness of the epicardial adipose tissue may serve as a marker for aortopathy induced by BAV. A second article by Tekinhatun et al.2 describe what they claim to be the first case report of compression of the left main coronary artery caused by the aneurysm of the main pulmonary artery secondary to the presence of quadricuspid pulmonary valve. The 37-year-old female patient had undergone surgical closure of atrial septal defect about two decades before. So the authors claimed that the abnormal valve leaflets caused pulmonary hypertension, leading to aneurysmal dilatation of the main pulmonary artery and subsequent coronary artery compression. Pulmonary hypertension, due to reasons other than the presence of quadricuspid pulmonary valve, can lead to aneurysmal enlargement of pulmonary artery (more than 40 mm dia), which can displace or compress the origin of the left main coronary artery.3 The cardiac OFT, formed by the progenitor cells derived from secondary heart field and immigrant NCC, was divided into proximal (conus cordis), middle, and distal (truncus) segments. The primitive heart tube consists of inner endocardium and an outer myocardium separated by an extracellular matrix substance called cardiac jelly. Proliferation of two types of cells in the cardiac jelly at the middle part of OFT lead to formation of two endocardial cushions. Endocardial cells covering the cushion undergo endothelial–mesenchymal transition regulated by bone morphogenetic protein, transforming growth factor beta, NOTCH signaling, and migrant NCC populate the endocardial cushions. In the distal OFT, two spirally arranged cushions develop, the parietal and the septal regulated by NCC cells. The parietal OFT cushion contributes to the left leaflets of aortic and pulmonary valves, while the septal OFT leaflet contributes to right leaflets. Anterior nonadjacent leaflet of the pulmonary valve and the posterior noncoronary, nonadjacent leaflet of the aortic valve develop from intercalated leaflet valve swellings, which are formed at the junction of SHF-derived myocardium proximally and SHF-derived smooth muscle cells distally.4–6 The bulky endocardial cushions slowly undergo a process of sculpting during prenatal period. The extracellular matrix forms a three-layered arrangement, lamina fibrosa made up of Collagen I and III on the aortic side, middle lamina spongiosa containing proteoglycans and glycosaminoglycans, and the thinnest ventricularis made up of elastin fibers. Scant literature is available on the maturation of the arterial valves and changes occurring in the composition of extracellular matrix during the late prenatal period.4 Congenitally diseased semilunar valves lead to valvular stenosis and/or insufficiency, arterial wall dilatation, and act as a substrate for infection, thrombus formation, arrhythmias, and even sudden death.5 Most common congenital semilunar valve anomaly is BAV with an incidence of up to 2% in general population. Incidence of unicuspid aortic valve is 0.02% and quadricuspid aortic valve is 0.013%–0.043%. The quadricuspid pulmonic valve is 9 times more common than the quadricuspid aortic valve, with an incidence of 0.02%–0.41%, with a male preponderance.7 Rarely, both aortic and pulmonary valve anomalies may coexist.8
C. S. Ramesh Babu (Thu,) studied this question.