Morphologic characteristics and structure of surface excrescences (Lambl's excrescences) in the normal aortic valve.

The incidence, morphologic characteristics and structure of surface valve excrescences (Lambl's excrescences) were studied by transmission and scanning electron microscopy of the aortic valve of 56 human subjects, age range birth to 91 years, without cardiac disease. Valve excrescences consisting of a core of connective tissue covered by the endocardium were observed in 90% of the subjects; the incidence was significantly lower in patients in the first decade of life. Two types of excrescences, lamellar and filiform, were found. Lamellar excrescences are located along the lower boundary of the lunulas and occurred more often in those younger than 30 years. Filiform excrescences appear most often in the nodulus Arantius and in the free-margin of the cusps. The excrescences of the nodulus are the most numerous. Free-margin excrescences are the least numerous and occur more frequently in persons older than 40 years. The connective tissue core of the filiform excrescences contains abundant collagen fibrils and elastic material arranged in apposed layers with different collagen fibril orientation. A circular zone devoid of identifiable connective tissue is present at the center of the filiform excrescences.