Lunules of semilunar leaflets of aortic valve

The lunules of the semilunar leaflets of the aortic valve are the small, crescent-shaped areas located at the free edge of each of the three aortic valve cusps (left coronary, right coronary, and noncoronary). Each cusp is attached to the aortic wall in a semilunar fashion, with the free edge forming the zone of coaptation during valve closure. The lunule is the thickened portion of the cusp edge, centrally located between the commissures, and is bordered by the thinner, more translucent regions of the leaflet edge. At the center of each lunule are the nodules of semilunar leaflets of aortic valve (nodulus of Arantius), a small fibrous nodule that enhances leaflet coaptation and prevents regurgitation during diastole.

Histologically, the lunule is composed of the same trilaminar structure as the rest of the leaflet: a collagen-rich fibrosa (aortic side), a proteoglycan-rich spongiosa (middle), and an elastin-rich ventricularis (ventricular side). The collagen bundles in the lunule region are densely packed, providing tensile strength for effective valve closure. T

he lunules are critical for the tight seal of the valve, and their integrity is essential for preventing aortic regurgitation. Fenestrations—small perforations—may occur in the lunule region, especially near the commissures, and are more common with aging, but do not always result in dysfunction.