Category: 7. Deep Vein Thrombosis False Positives

A groin hematoma occurs when blood leaks from an artery, typically the femoral artery, and causes localized swelling. Some risk factors can include recent procedure in that area, obesity, anticoagulation, and peripheral vascular disease (Kosmidou & Karmpaliotis).

On ultrasound, a groin hematoma will be hypoechoic with some anechoic areas scattered throughout. If you scan the hematoma in the longitudinal view, it becomes obvious that the object is circumscribed and not tubular like a vein or artery.

A pseudoaneurysm occurs when there is a partial rupture of an artery wall that leads to an outpouching of the artery with the accumulation of periarterial blood. This most commonly occurs from arterial trauma from an interventional medical procedure, gunshot, or a stab wound (Montorfano et al). These sites can become infected and give off emboli.

On ultrasound, pseudoaneurysms present as anechoic or hypoechoic images, sometimes with moving echoes. With Color Doppler, you can see a “Yin-Yang Sign” from the circular motion of blood inside the pseudoaneurysm cavity. In systole, blood flows towards the pseudoaneurysm cavity (red) while in diastole the blood moves back towards the arterial lumen (blue)(Montorfano et al).

Lymph nodes are part of the adaptive immune system and can become inflamed when the body is fighting an infection.

On ultrasound, a lymph node can look similar to a clot because it is a hypoechoic oval structure with a hyperechoic center. However, if you scan the lymph node in the longitudinal view, it becomes apparent that the object is circumscribed and not tubular in structure like a vein (Zitek, Baydoun & Baird). Lastly, a lymph node will disappear quickly if you attempt to trace it up and down, unlike an artery or vein that will be continuous structure.

A Baker’s cyst is a fluid-filled cyst in the popliteal bursa on the back of the knee. This can result from inflammation of the knee joint or a knee injury, like a cartilage tear.

These popliteal cysts can present with similar symptoms as a deep vein thrombosis such as sharp knee pain, calf swelling, and occasionally erythema.

On ultrasound, a Baker’s cyst appears as a circular anechoic mass with sharply defined borders in both the longitudinal and transverse view (Zitek, Baydoun & Baird). On Color Doppler, there should be no flow.

Superficial thrombophlebitis occurs when there is a clot in a superficial vein, like the great and small saphenous veins and the varicose veins.

A clot in a superficial vein will show the same signs on ultrasound as in a deep vein; you can see an echogenic mass with direct visualization, non-compressibility, and decreased or absent color flow. The major difference is that superficial veins do NOT accompany arteries while deep veins do (Naringrekar et al).

This pitfall is more likely in obese patients whose superficial veins are enlarged and can be mistaken as deep veins.

There are a few structures that can be mistaken for a deep vein thrombosis because they look like non-compressible vessels. These include superficial thrombophlebitis, Baker’s cysts, lymph nodes, pseudoaneurysms, and groin hematomas, which we will show below.

To help avoid these false positives, be sure to always identify that the vein is next to an artery. Additionally, if you compare the vein in Short Axis and Long Axis views, it will look circular in the short axis view and cylindrical in the long axis view.