DEVELOPMENT OF THE INFERIOR VENA CAVA

Basic knowledge of the IVC embryogenesis is essential to understand the related anomalies.

The embryologic period encompasses a series of transformations in several venous networks. Connections between precursor veins form the four different parts of the definitive IVC – hepatic, suprarenal, renal and infrarenal.

The mesonephros becomes well vascularized during gestational week 4. By that time it is drained by the parallel posterior cardinal veins. After week 4 the drainage of the mesonephros is done by the recently developed subcardinal veins. They anastomose with: 1. the posterior cardinal veins; 2. the vitelline veins (the latter drain blood from the yolk sac) through the right subcardinal vein and that connection later forms the suprarenal portion of the IVC; 3. with each other, forming the intersubcardinal anastomosis which later develops into the renal portion of the IVC. The vitelline veins define the hepatic portion of the inferior vena cava. Further development causes the left subcardinal vein to give rise to the left renal vein and the left gonadal vein. Part of the right subcardinal vein forms the right gonadal vein. The posterior cardinal veins start to disappear by week 6. Their most distal parts persist and will later become the common iliac veins. Another parallel venous system develops during weeks 6 and 7 – the supracardinal veins. The hemiazygos vein is formed by the left supracardinal vein and the azygos vein is formed by the right supracardinal vein. The azygos vein on the right drains blood from the iliac veins and binds with the intersubcardinal anastomosis and thus forms the infrarenal portion of the definitive inferior vena cava.

Fig. 1: Normal blood drainage by the main venous vessels.
References: Georgi Valchev, MD

INFERIOR VENA CAVA ANOMALIES

Since the inferior vena cava if formed by many transforming venous vessels it is easy to conclude that this might lead to a number of different anomalies.

Save the absence of the inferior vena cava, there are several other anomalies that are worth mentioning. They are presented in the table below:

Table 1: Anomalies of the inferior vena cava (besides absence of the IVC).
References: Department of Diagnostic Imaging, St. Marina University Hospital, Varna/ Bulgaria. See references.

ABSENCE OF INFERIOR VENA CAVA

The absence of the inferior vena cava (AIVC) is an even rarer abnormality with very few cases reported in the past – during dissections, surgery or in the course of unsuccessful cardiac catheterization. In the last decades, following vast leaps in the development and accessibility of cross-sectional imaging techniques, newly acquired data has led to an increase of the known prevalence of the condition. But even though it is now more frequently diagnosed and recognized, it still remains a very rare condition with an estimated prevalence of about 0.001%.

In the most common pathway of the venous flow the internal and external iliac veins continue to the lumbar veins Fig. 3 . The latter and the anterior paravertebral collateral veins anastomose with the azygos-hemiazygos system Fig. 4 , which empties into the right atrium through the superior vena cava Fig. 5 .

In some reported cases the two renal veins do not drain in collateral networks but form an inferior vena cava that runs in a normal manner cranially (so only the infrarenal portion of the IVC is missing).

Looking back to the embryology of the IVC, it is implied that an absence of the entire vein should be caused by a failure in the normal course of development of the three aforementioned embryologic venous systems – the posterior cardinal, the subcardinal and the supracardinal veins.

Although most authors believe that these are embryologic events, a number of recent studies suggest that the absence of the IVC, especially of a segment, may be due to perinatal thrombosis.

From a genetic point of view, a first degree relative with an IVC anomaly is considered a risk factor.

Like many other congenital anomalies, an association with other abnormalities such as congenital heart disease and heterotaxy syndromes is sometimes present.