Rush Center for Congenital
and Structural Heart Disease



Systemic venous system

At day 21 there is a common atrium as a result of fusion of the two endocardial tubes with two sinus horns, a left and a right horn, representing the non fused ends of the endocardial tubes [362].  These two horns will form the sinus venosus.

The sinus venosus lies dorsal to the atria.  The following veins drain into the sinus venosus on each side:  The common cardinal vein, which drains from the anterior cardinal vein (draining the cranial part of the embryo) and the posterior cardinal vein (draining the caudal part of the embryo), the umbilical vein (connecting the heart to the primitive placenta) and the vitelline veins (draining the yolk sac, gastrointestinal system and the portal circulation).

At week 4 of development the sinus venosus opens to the common atrium.  In week 7, the sinoatrial communication becomes more right sided, thus connecting it to the right atrium.  At week 8 of development the distal end of the left cardinal vein degenerates, and the more proximal portion of it will now connect through the anastomosing vein (left brachiocephalic vein to the right anterior cardinal vein (right brachiocephalic vein), thus forming the superior vena cava.  The left posterior cardinal vein also degenerates, and the left sinus horn receiving venous blood from the heart becomes the coronary sinus.  The right vitelline vein becomes the inferior vena cava, and the right posterior cardinal vein becomes the azygos vein.  All this is completed in the week 8 of development.  The left umbilical vein degenerates and the right umbilical vein connects to the vitelline system through the ductus venosus (which is derived from the vitelline veins) [375]. (Figure 7)



Figure 7

Development of the systemic venous drainage:  These are dorsal views of the heart.  (a) At week 4 of development, depicts symmetrical systemic venous drainage into the two sinus venosus horns. (b) At week 7 of development, depicts degeneration of some of the systemic veins.  (c)  At week 8 of development, depicts the central systemic venous anatomy as seen in a born child.