Deep Venous Thrombosis

Compression ultrasound relies on the fact that the normal venous system can be coapted by pressure applied with the ultrasound transducer (approximating the venous walls, figure 1). If DVT is present, the vein will not be completely compressible (figure 2).

Figure 1. Ultrasound Evaluation of DVT: Normal compression sonography

Rest (left) and compression (right) ultrasound images show that the vein is compressible, a normal finding.

Figure 2a. Ultrasound Evaluation of DVT

Rest (fig. 2a) and compression (below, fig. 2b) ultrasound images show that the common femoral vein is not completely compressible due to the presence of acute DVT.

The location of the vein is marked by calipers.

Figure 2b. Ultrasound Evaluation of DVT: Venous thrombosis



Figure 3. Color Doppler

Longitudinal ultrasound image shows normal color Doppler signal filling the external iliac vein, indicating venous patency.

In a vein completely occluded by DVT, no color Doppler flow will be present. The color Doppler signal will be deviated around partial venous thrombosis.

Duplex Doppler is used to detect the presence of calf-vein thrombosis (which is quite difficult to visualize with ultrasound, due to the small size of the vessels in question) or thrombosis of the inferior vena cava (IVC). For the detection of calf-vein thrombosis, the ultrasound transducer is placed over the deep femoral system, and the calf is squeezed manually. If the calf veins are patent, an abrupt increase in the flow velocity within the deep femoral system should be seen as blood is expressed from the calf veins. This increase is referred to as "flow augmentation." Absence of appropriate flow augmentation raises the possibility of calf-vein thrombosis. The presence of IVC thrombosis may be inferred from alterations in the usual duplex Doppler wave forms that occur as a result of the normal phasicity of lower-extremity venous flow (which is due to the normal respiratory cycle).

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