What is inferior vena cava

Inferior vena cava is a large retroperitoneal blood vessel formed by the confluence of the right and left common iliac veins (usually occurs at the L5 vertebral level) that is responsible for transporting deoxygenated blood from the body regions inferior to the diaphragm (lower extremities and abdomen) back to the right atrium of your heart. The inferior vena cava lies along the right anterolateral aspect of the vertebral column and passes through the central tendon of the diaphragm around the T8 vertebral level. Inferior vena cava has the largest diameter of the venous system and is a thin-walled vessel. These anatomic characteristics make it ideal for transporting large quantities of venous blood. Many veins contain one-way valves to ensure the forward flow of blood back toward the heart. The inferior vena cava, however, does not contain such valves, and forward flow to the heart is driven by the differential pressure created by normal respiration. As the diaphragm contracts and creates negative pressure in the chest for the lungs to fill with air, this pressure gradient pulls the venous blood from the abdominal inferior vena cava into the thoracic inferior vena cava and subsequently into the right heart. The inferior vena cava enters the right atrium of the heart after coursing through the diaphragm, entering the posterior inferior aspect of the atrium. The inferior vena cava enters the right atrium inferior to the entrance of the superior vena cava.

The inferior vena cava is a mostly symmetric vessel with a few exceptions. Due to the inferior vena cava residing on the right side of the vertebral column the vessels entering the inferior vena cava from the left side of the body, like the left renal vein, are longer than their anatomic counterparts on the right. Other left-sided veins, like the left adrenal and left gonadal vein, first join the left renal vein before joining the inferior vena cava and continuing as venous flow returning to the heart. This differs from the right side of the body where the right adrenal and right gonadal vein directly join the inferior vena cava without first joining the right renal vein. Anatomic variants venous of anatomy involving both right and left sides have been described ¹⁾.

Blood from the left and right femoral veins enters the inferior vena cava via the left and right common iliac veins, respectively. Blood from the abdominal viscera travels into the portal vein and enters the inferior vena cava via the hepatic veins after traversing the liver and its sinusoids. Venous blood from the abdominal wall reaches the inferior vena cava through lumbar veins. Ascending lumbar veins connect lumbar veins to the azygos vein and this provides some collateral circulation between the inferior vena cava and the superior vena cava ²⁾. This potential for collateral flow could be critical if either of the larger veins becomes obstructed.

Below is a list of (most common) vertebral levels at which different veins enter the inferior vena cava:

• T8: Hepatic veins, inferior phrenic veins
• L1: Right suprarenal vein, renal veins
• L2: Right gonadal vein
• L1-L5: Lumbar vertebral veins
• L5: Right and left common iliac veins

Blood Supply and Lymphatics

Blood supply to the inferior vena cava is derived partially from the deoxygenated blood it carries towards the heart and partially supplied by the vasa vasorum that penetrate the tunica adventitia of the vessel ³⁾.

Nerves

The inferior vena cava receives autonomic innervation from the splanchnic nerves ⁴⁾. This innervation serves to alter the diameter of the inferior vena cava via interactions with alpha-1, alpha-2, and beta-2 receptors.

Muscles

As in all vasculature, the inferior vena cava contains three layers: the tunica intima, the tunica media, and the tunica adventitia. The tunica media layer of the inferior vena cava contains smooth muscle responsive to the input from the nervous system ⁵⁾. No other muscles are found in the inferior vena cava.

Figure 1. Inferior vena cava

Figure 2. Heart

Inferior vena cava physiologic variants

There are many physiologic variants of the inferior vena cava ⁶⁾. Compared to the arterial system the venous system is much more susceptible to congenital malformations, many of which remain asymptomatic throughout a patient’s life. If symptoms are present, they are often vague and include abdominal pain or low back pain. Some of the more clinically significant physiologic variants are listed below.

• Left Inferior Vena Cava: This anomaly is caused by regression of the right supracardinal vein and the persistence of the left supracardinal vein. The left inferior vena cava is joined by the left renal vein and then crosses anterior to the aorta before it joins the right atrium, forming a normal pre-renal inferior vena cava. This anomaly has a suspected prevalence of 0.2% to 0.5%.
• Double Inferior Vena Cava: This anomaly is caused by the persistence of both the left and right supracardinal veins. A prevalence of 0.2% to 0.3% is suspected.
• Intrahepatic Inferior Vena Cava Agenesis: Congenital anomaly resulting in the lack of the intrahepatic inferior vena cava. Intrahepatic venous supply bypasses the hepatic inferior vena cava through the azygous/hemiazygous venous system ⁷⁾.
• Absent Infrarenal Inferior Vena Cava: This is the rarest of the physiologic caval anomalies. The suspected and currently accepted etiology of absent infrarenal inferior vena cava is intrauterine or perinatal thrombosis and resultant degeneration of the infrarenal inferior vena cava ⁸⁾.

What does the inferior vena cava do?

Inferior vena cava is ultimately responsible for the transport of almost all venous blood (deoxygenated) from the abdomen and lower extremities back to the right side of your heart for oxygenation.

Inferior vena cava syndrome

Inferior vena cava syndrome is caused by inferior vena cava obstruction. There are many causes of inferior vena cava syndrome such as thrombosis, tumor thrombosis, iatrogenic occlusion caused by liver transplantation, congenital abnormality such as Budd-Chiari syndrome, compression by extravascular neoplasm, liver abscess, retroperitoneal fibrosis, or uterus during the third trimester of pregnancy ⁹⁾. Inferior vena cava thrombosis is a difficult clinical scenario. Although it can be asymptomatic, inferior vena cava thrombosis can also present with a myriad of symptoms. These are usually non-specific like abdominal or back pain, but may also include leg cramping, swelling, or pain. Treatment is based on patient condition/symptoms and can include anticoagulation, clot and/or filter (if present) removal via Interventional Radiology techniques or rarely open surgical technique. The most common cause of inferior vena cava thrombosis in a patient without anatomic variants is previous inferior vena cava filter placement.

The symptoms of inferior vena cava syndrome (inferior vena cava obstruction) are dependent upon the level of obstruction and they include intravascular hypovolemia, liver damage, kidney damage, edema of lower extremities, and ileus ¹⁰⁾. In rare occasions, intravascular hypovolemia caused by inferior vena cava obstruction induces circulation collapse and result in shock, a life-threatening condition ¹¹⁾. The treatments of inferior vena cava syndrome (inferior vena cava obstruction) are varied according to the cause of inferior vena cava syndrome (inferior vena cava obstruction). Obstruction of vena cava by extravascular compression from a malignant tumor can be treated by irradiation ¹²⁾ or endovascular stent placement ¹³⁾.

Inferior vena cava filter

An inferior vena cava filter is a small device that is placed in your inferior vena cava to prevent blood clots from moving through your blood into your lungs (pulmonary embolus) (see Figure 3). Although there is some controversy over inferior vena cava filter indications, recurrent deep venous thromboses and consequent pulmonary emboli refractory to treatment with anticoagulation may require placement of an inferior vena cava filter ¹⁴⁾. Certain institutions also advocate for inferior vena cava filter placement for high risk trauma patients (even without documented clot). Inferior vena cava filters may be permanent or retrivable, although data suggests that only a fraction of the retrievable filters are later removed. Anatomic variations from the norm require careful attention to detail and understanding of their manifestations and potential complications during procedures. A pulmonary embolus is a blockage in the main artery of a lung. Inferior vena cava filters can be used to prevent or manage pulmonary emboli and deep vein thrombosis (DVT), and can be temporary or permanent. The shape of an inferior vena cava filter resembles that of an umbrella, and it functions in a similar way.

Figure 3. Inferior vena cava filter

Your inferior vena cava filter will be placed by your interventional radiologist. An interventional radiologist is a doctor who specializes in image-guided procedures. The interventional radiologist will insert a 3 mm plastic tube (called a sheath) by going through a vein in your neck or groin. Your doctor will position the filter in the vein using a fluoroscopy (real-time x-rays). Your doctor will guide the sheath to the blood clot in the inferior cava vein, which is where the inferior vena cava filter will be placed.

The procedure will take about 30 minutes, but you should expect to be in the procedure room for about an hour. You will have a follow-up appointment 4 to 6 weeks after placement to see when your inferior vena cava filter can be removed.

If you receive a temporary inferior vena cava filter, the interventional radiologist will remove the filter after the necessary period of time has passed. To remove the inferior vena cava filter, the interventional radiologist will insert a long plastic tube and a goose-neck system (like a miniature lasso) as before and use this to remove the inferior vena cava filter.

Inferior vena cava filter indications

There are a number of treatments available to manage or prevent pulmonary emboli and DVT, including conservative (medical) therapy, inferior vena cava filters, intravenous systemic thrombolysis, catheter thrombolysis and a surgical operation.

Your suitability for this treatment depends on a number of factors, including how stable your blood pressure is and how well your heart is working. Other factors which will be taken into consideration are the type of inferior vena cava filter and your clinical situation, as permanent placement means you will need to take medication to prevent blood clotting for the rest of your life.

Two guidelines, both from 2006, recommend the placement of retrievable (temporary) inferior vena cava filters whenever reversible contraindications to anticoagulation are present ¹⁵⁾. These contraindications include recent hemorrhage, surgery, major trauma, etc.). Other circumstances include embolic prophylaxis during the mechanical removal of a thrombus, and in the setting of a massive or submassive pulmonary embolus. In each of these cases, the filter may be retrieved after anticoagulation is resumed. Alternatively, permanent filters may be deployed in individuals who are not anticipated to be candidates for systemic anticoagulation. Occasionally, patients with reversible contraindications to anticoagulation will not have their temporary inferior vena cava filter retrieved and it will become permanent. Regardless of the indication for placement,

In summary, patients with inferior vena cava filters – particularly permanent filters – are at increased risk for recurrent DVT. Judicious use of inferior vena cava filters, as well as prompt retrieval of inferior vena cava filters that are intended to be temporary, substantially reduces the risk of inferior vena cava thrombosis ¹⁶⁾.

Inferior vena cava filter risks

There are some minor risks, including infection and bruising at the puncture site in your neck or groin. Major risks include the filter moving to another part of your body, the development of another thrombus, or a leg of the inferior vena cava filter breaking through the wall of the vein, which can be painful.

If you have a permanent inferior vena cava filter, the medication preventing blood clots that you will need to take carries further risks.

After your inferior vena cava filter procedure

In the recovery room

You will be taken to the recovery room or hospital bed.

Your nurse will explain your discharge instructions to you and your caregiver before you go home. They will also give you a wallet card with information about your inferior vena cava filter to keep with you.

Wearing a seatbelt may put pressure on your incisions. You may want to place small pillow or folded towel between the strap and your body when you go home.

At home

Caring for yourself

• Leave the bandage on the insertion site for 24 hours. After 24 hours, you can take it off.
• Your incision may feel sore. This should get better within a day or 2. You can take over-the-counter pain medication, such as acetaminophen (Tylenol®) or ibuprofen (Advil®), if you need it.
• You can shower 24 hours after your procedure.

Activities

• For the first few days, you should avoid certain activities, such as exercises that involve stretching.
• You can still have a magnetic resonance imaging (MRI) while you have an inferior vena cava filter, but it’s important to tell the healthcare provider at the radiology facility each time to be safe. Show them the wallet card your nurse gave to you.
• Your inferior vena cava filter will not set off metal detectors.

Call your doctor if you have:

• A temperature of 100.4° F (38° C) or higher
• Pain around your insertion site that doesn’t go away after taking medication
• Drainage around the incision site
• Redness and swelling around your insertion site