What is a NIVL?

What is NIVL?

NIVL stands for non-thrombotic iliac vein lesion. This vascular occurrence was previously coined May-Thurner Syndrome, after the doctors who discovered the phenomena. NIVL is caused when the left iliac vein is compressed by the right iliac artery. This incidence increases a patient's risk significantly of developing blood clots.

How was NIVL discovered?

In 1851, Rudolf Virchow observed that patients were five times more likely to develop blood clots in the left iliofemoral vein compared to the right.

Figure 1: Diagram of common iliac veins and arteries

In 1957, May and Thurner provided an explanation of this phenomenon. They found that the left common iliac vein had a vascular thickening at the point where it was crossed by the overlying right common iliac artery. They called this lesion, “a venous spur” and suggested that the chronic pulsation of the overlying iliac artery is responsible for the formation of this spur. They continued that the spur is what leads to a venous obstruction. This anatomic variant later became widely recognized as the May-Thurner syndrome (MTS). Recently, this definition has been expanded to a broader disease profile known as NIVLs.

What exactly is a venous spur?

A venous spur occurs as a result of the trauma induced by the direct pulsation of an artery

Figure 2: Diagram of compressed iliac veins

against a vein. This chronic force on the vein leads to the build up of elastin and collagen on the inner side of the vein wall. The resulting potential appearances of a cross section of the internal left common iliac vein are demonstrated in Figure 2.

How many people have NIVL?

The actual number of people who suffer from NIVL is unknown. According to autopsy studies performed in the early twentieth century, it is believed that between 22 and 32% of people develop NIVL throughout their lifetime.

What are the symptoms of NIVL?

People are often diagnosed with NIVL after seeking treatment for left lower extremity swelling, pain, or tenderness. Their primary care doctor often sends them for an ultrasound study to rule out a deep vein thrombosis (DVT), or blood clot.

How is NIVL diagnosed?

After a blood clot has been ruled out using ultrasound, the patient will undergo a CT of their abdomen and pelvis. The CT imaging will give the physician their first clear image of the compressed iliac vein. However, a patient will not have a definitive diagnosis of a non-thrombotic iliac vein lesion until a Venogram is performed.

How is NIVL treated?

During a venogram, a special dye is injected into the veins. This dye allows the veins to be photographed using x-ray imaging. Venograms are a diagnostic radiology tool. At Milford Vascular Institute in our Outpatient Based Laboratory, once a diagnosis is confirmed for NIVL, a stent can be placed inside the left common iliac vein to expand and reopen the vein.