The syndrome of absent pulmonary valve and ventricular septal defect--anatomical features and embryological implications.

Four cases of absent pulmonary valve in combination with ventricular septal defect are reported. In this syndrome hypo- and dysplasia of the pulmonary valve is constantly associated with a big ventricular septal defect, formation of a huge pulmonary artery aneurysm and absence of the ductus arteriosus. Presence or absence of a right ventricular outflow tract obstruction is the criteria for classification into two forms. Absence of the pulmonary valve, right ventricular outflow tract obstruction and a malalignment-type ventricular septal defect produced by a conotruncal malseptation process represent the primary complex of malformations. Consecutive intrauterine cardiac failure is most probably prevented by prenatal closure of the ductus arteriosus. Pulmonary artery aneurysm and also dilatation of the right ventricular outflow tract as well as a whole lot of other coexisting deformities can be explained by a cascade of hemodynamical sequelae started by this ductus closure in utero. An embryological scheme explaining the genesis of this syndrome is derived from a morphological analysis of the constituting incoherent-appearing anatomical features.