ANATOMY OF THE DUCTUS VENOSUS

• Lies within the two layers of lesser omentum (hepato-gastric ligament) in a groove between the left and caudate lobes of the liver and closes, within 2 weeks, after birth.
• Originates from the Umbilical Vein
• Courses posterior in a cephalad direction with increasing steepness.
• Enters the IVC just below the diaphragm.
• The velocity increases dramatically as the blood leaves the umbilical vein through the inlet of the ductus, and represents the highest blood velocity in the fetal venous system. It is usually about 50 cm/s in early pregnancy (10-15 wks), and may exceed 65 cm/s near term (1). Aliasing at the isthmus of the ductus venosus during color doppler interrogation is thought represent high laminar velocity and “possibly vortices rather than turbulent flow” (1).
• Diameter < 1/3 of umbilical vein and this accelerates blood flow velocity (maximum inner width of narrowest portion = 2 mm).
• Functionally, the ductus venosus is linked to the foramen ovale due to “preferential streaming of umbilical blood” to the left atrium. A second important source for streaming umbilical blood is that portion that flows through the left portion of the liver where oxygen extraction is modest (10-15%). Once it reaches the IVC, the blood flows in a near vertical direction, and laminar flow prevents extensive mixing of oxygenated and deoxygenated blood. These events are thought to be controlled by the position of the crista dividens in the fetus (situated further to the right than in neonates).
• Two separate pathways therefore exist:
1. Ductus - LA Pathway.
2. IVC - RA Pathway.

REFERENCES

1. Kiserud T. The ductus venosus. Semin Perinatol 2001;25(1):11-20.