The Anatomy of the Inferior Vena Cava

The inferior vena cava (also known as IVC or the posterior vena cava) is a large vein that carries blood from the torso and lower body to the right side of the heart. From there the blood is pumped to the lungs to get oxygen before going to the left side of the heart to be pumped back out to the body.

The IVC gets its name from its structure and location. It is the lower, or inferior, part of the vena cava, which transports blood back to the right side of the heart. The IVC carries blood from the lower body while another vein, known as the superior vena cava, returns blood from the upper half of the body to the heart.

Anatomy

The IVC is formed by the merging of the right and left common iliac veins. These veins come together in the abdomen, carrying blood from the lower limbs.

Structure

The IVC goes from the diaphragm into the right side of the heart, beneath the entrance of the superior vena cava.

A few veins merge and drain into the IVC before it makes its way up to the heart:

• The left renal vein, the left adrenal vein, and left gonadal veins merge into the renal vein.
• On the right side, the right adrenal and right gonadal veins enter directly into the IVC without merging into the right renal vein first.

This makes the IVC almost symmetrical. Other veins that enter the IVC include the hepatic veins, inferior phrenic veins, and lumbar vertebral veins.

Absence of Valves

What makes the IVC different from other veins is that there are no valves within this vein to keep blood moving forward instead of backward. To prevent blood from moving back into the body, other veins have valves that close as the blood flows past them.

Blood is pulled forward from the IVC all the way up to the heart due to the contraction of the diaphragm as the lungs fill with air.

Location

The IVC starts in the lower back where the right and left common iliac veins (two major leg veins) have joined together. It runs under the abdominal cavity along the right side of the spinal column and enters the right atrium of the heart from the back of the heart.

From here, blood will pump out to the lungs for oxygen supply before traveling to the left side of the heart to be carried out to the body once again.

Anatomical Variations

There are some congenital variations in IVC structure, and these are difficult to detect. Often a person won’t have any symptoms to signal a defect in the IVC. Symptoms, when they do occur, can include vague low back or abdominal pain.

Some variations of the IVC:

• A left IVC occurs when the left renal vein joins the left IVC but then crosses in front of the aorta before entering the right atrium of the heart. Left IVC has a prevalence rate of 0.4% to 0.5%.
• A duplicate or double IVC is when there are two IVC veins instead of one. Its prevalence rate is typically 0.2% to 0.3%.
• Azygous continuation of the IVC, where blood coming from the lower body drains into a different venous system called the azygous system. This system drains the thoracic wall and upper lumbar area of blood.
• A rare variation is called absent infrarenal IVC. This results in the partial or complete absence of the IVC, likely due to another variation of the veins which merge into the IVC.

Function

The primary function of the IVC is to carry deoxygenated blood that has circulated through the lower half of the body back to the right atrium of the heart. The IVC is responsible for returning all of the blood below the diaphragm, while the superior vena cava returns the blood above the diaphragm to the heart.

Clinical Significance

The most common surgical procedure involving the IVC is the placement of an inferior vena cava filter. An IVC filter stops blood clots that form in the veins of the lower half of the body from traveling up to the heart and lungs, potentially causing a pulmonary embolism (a blockage in the lung which can prevent blood flow).

An IVC filter is commonly recommended when medications used to treat blood clots, such as blood thinners, aren't effective or are contraindicated. Depending on the severity and frequency of the blood clots, IVC filters can be left in permanently or removed once the risk of clots forming and traveling to the lungs has passed.

In some cases, an IVC filter that has not been removed may cause IVC thrombosis, creating blood clots in the IVC itself. For this reason, an IVC filter is monitored to determine the best time to remove it to prevent blood clots from forming.