Chapter 126. Development of The Venous System: The Inferior Vena Cava - Review of Medical Embryology Book

The inferior vena cava: a series of successive venous networks take part in the formation of the inferior vena cava. Each predominates temporarily, then regresses, and remains only partly in the final definitive system

THE MESONEPHROS grows considerably and becomes very highly vascularized during week 4. Although it is drained initially only by the posterior cardinal veins, a new system takes over after week 4, the subcardinal network, which is formed by the internal veins of the wolffian body

The internal veins of the wolffian body are widely anastomosed with the initial posterior cardinal network and with each other, forming the median subcardinal network, which soon predominates. It takes over the posterior cardinal system, which disappears in the middle region of the embryo
The subcardinal sinus persists as the left renal vein
The anterior segment of the left subcardinal vein disappears, but its posterior segment forms the left gonadal vein
The right subcardinal vein forms the right gonadal vein and the pararenal portion of the definitive inferior vena cava

Cranially, it continues with the mesenteric segment and the hepatic segment derived from the hepatic vein (proximal right vitelline} and hepatic sinusoids

DURING WEEKS 6 AND 7, a supplementary dorsal network develops, called the supracardinal system, which runs parallel to the paravertebral sympathetic chain and opens into the proximal segment of the posterior cardinal veins. Anastomoses are formed

Between the two supracardinal veins
Between the supracardinals and the subcardinals, on the right side
Between the extremities of the posterior cardinal veins
The left supracardinal vein becomes the hemiazygos vein and is drained toward the right by the transverse anastomosis which forms an interazygos communication
The right supracardinal vein becomes the azygos vein, which opens into the right anterior cardinal vein

From below, the azygos vein drains the 2 iliac veins, thus becomes the prerenal portion of the definitive inferior vena cav

IN SUMMARY: the definitive inferior vena cava is composed of (from caudal to cranial)

MALFORMATIONS of the inferior vena cava may be due to the complexity of formation of the system, yet, even in cases of severe malformation, one of the constituent networks invariably substitutes some form of venous flow

Agenesis (absence) of the inferior vena cava is the most conspicuous. The right subcardinal vein has failed to make its connection with the liver and shunts blood directly into the right supracardinal vein. Thus, blood from the caudal part of the body reaches the heart via the azygos and superior vena cav The hepatic vein enters the right atrium at the site of the inferior vena cava
An abnormality of position of the vein may affect the adjacent organs, such as the ureter, compressing it and causing a hydronephrosis
Double inferior vena cava at the lumbar region: the left sacrocardinal vein has failed to lose its connection with the left subcardinal, and the left common iliac vein may or may not be present. The left gonadal vein is usually present and in a normal condition