The Anatomy of the Inferior Vena Cava

It's responsible for carrying lower body blood back to the heart

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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, as it is the lower, or inferior, part of the venae cavae, which are the two large veins responsible for the blood transport back to the right side of the heart. The IVC handles blood from the lower body while the other vein, known as the superior vena cava, carries the blood circulating in the upper half of the body.

Anatomy

The IVC is formed by the merging of the right and left common iliac veins. These veins come together in the abdomen, helping to move blood from the lower limbs back up to the heart.

The IVC is one of the largest veins in the body, which is helpful for the large volume of blood it’s responsible for carrying.

Structure

What makes the IVC different from other veins is that there are no valves within the vein to keep blood moving forward instead of backward, which is how the typical anatomy of a vein works. To prevent the blood from moving back into the body, valves made up of tissue in the vein close as the blood through it.

But the anatomy of the IVC vein is slightly different. Instead of valves, the pressure from breathing and the contraction of the diaphragm as the lungs fill with air helps to pull the blood forward from the IVC all the way up to the heart. 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, including the left renal vein. The left adrenal and left gonadal veins go into the renal vein before all shifting to the IVC.

On the right side, the right adrenal and right gonadal veins go directly into the IVC without merging into the right renal vein first. This makes the IVC almost symmetrical.

Other veins that enter into the IVC through the spinal cord include the hepatic veins, inferior phrenic veins, right suprarenal vein, and lumbar vertebral veins.

The IVC’s job is to drain all the blood from the lower half of the body including the feet, legs, thighs, pelvis, and abdomen.

Location

The IVC starts in the lower back where the right and left iliac veins (two major leg veins) have joined together. Once the IVC is formed it runs under the abdominal cavity along the right side of the spinal column. It goes into the right atrium of the heart, in through the back side.

From here, blood transported by the IVC and superior vena cava will pump out to the lungs for oxygen before traveling to the left side of the heart to be carried out to the body once again.

Anatomical Variations

It’s possible for the IVC to have a congenital difference, and these are difficult to detect. Often a person won’t have any symptoms to signal a defect in the IVC, but some common symptoms include abdominal or low back pain.

Some variations of the IVC are the left IVC, which happens when the left renal vein joins the left IVC but then crosses in front of the aorta before going into the right atrium if the heart. Left IVC has a prevalence rate of 0.2% to 0.5%.

Another common variation is a duplicate or double IVC. In this case, a double IVC is just that: two IVC veins instead of one. Its prevalence rate is typically 0.2% to 0.3%.

Other variations may include an intrahepatic IVC agenesis, where the intrahepatic veins skip the hepatic IVC entrance and go into a different venous system called the azygos system. This system drains the thoracic wall and upper lumbar area of blood.

The last, extremely 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 moving all of the blood below the diaphragm, while the superior vena cava handles the blood above the diaphragm.

Clinical Significance

The IVC is most commonly used for IVC filter placement, which can help reduce the risk of pulmonary embolisms (a blockage in the lung which can prevent blood flow). An IVC filter stops blood clots that form in the veins of the lower half of the body, or someone who suffers from deep vein thrombosis, from having those clots reach the lungs.

An IVC filter is commonly used in patients that aren’t responding to medication for blood clots such as blood thinners. 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. This is why if needed your physician will monitor the IVC filter and determine the best time to remove it to prevent blood clots from forming.

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