Normal development of the pulmonary veins in human embryos and formulationat a morphogenetic concept for sinus venosus defects

A sinus venosus defect is a form of interatrial communication associated wi th abnormal drainage of the right pulmonary veins. Its morphogenesis still remains unclear. We therefore studied the normal development of pulmonary v eins in human embryos in relation to the sinus venosus and the dorsal mesoc ardium using graphic reconstructions and HNK-1 immunohistochemistry, Twenty embryos, ranging from 4 to 7 weeks' gestation, were examined. At 4 weeks, the orifice of the nonlumenized common pulmonary vein is visible as an endo thelial invagination within the sinus venosus segment. Development of the m uscular septum primum and the ventral proliferation of extracardiac mesench yme from the dorsal mesocardium positions the common pulmonary vein (CPV) e ventually into the left atrium, The right wall of the CPV contributes to th e posterior part of the atrial septum and is continuous with the dorsal sin uatrial fold (the future left venous valve). With the use of HNK-1 antigen expression as a marker for sinus venosus myocardium, this common wall betwe en the right-sided sinus venosus and the CPV is demonstrated, and at 7 week s the proximal port of the right upper pulmonary vein also becomes part of this common wall. This study demonstrates that the CPV develops within the sinus venosus segment and that later a common myocardial wall is present be tween the sinus venosus in the right atrium and the CPV. A deficiency of th is wall explains the development of sinus venosus defects. (C) 2001 by Exce rpta Medico, Inc.