Quadricuspid pulmonary valve: macroscopic and microscopic morphometric examination.

A quadricuspid pulmonary valve obtained upon autopsy of a 26-year-old male was examined. The macroscopic evaluation revealed three normal (posterior, right anterior and left anterior) leaflets and one additional leaflet of the pulmonary valve. Except that, the heart showed neither other anatomical variabilities nor any signs of heart disease. The additional leaflet was located between the left anterior and right anterior leaflets and was significantly smaller in size. Under the microscope, all leaflets showed preservation of the typical, layered structure. The thickness and extracellular matrix composition of the particular layers differed between the leaflets. Right ventricular myocardium (myocardial sleeves) exceeded the level of the hinge line in all three normal leaflets, which was not observed in the additional leaflet. Autonomic nerves and ganglia were not seen in the perivalvular epicardial adipose tissue surrounding the additional leaflet. The sinus wall of all the leaflets revealed typical organization of collagen bundles as well as elastic fibers and showed no signs of disruption. The abnormality seen in the structure of the pulmonary valve is likely to be a result of disturbed embryonic development and may affect the clinical management of patients with such variation.