How is extremity deep vein thrombosis diagnosed sonographically?
US is the initial imaging study of choice for evaluating suspected upper or lower extremity deep vein thrombosis (DVT). In symptomatic patients, the sensitivity and specificity of US for DVT is at least 95% and 98%, respectively. The most important sonographic feature used to diagnose DVT is venous compressibility. Normally, the deep extremity veins are fully compressible. In contrast, thrombosed veins will not fully compress. The gray scale luminal echogenicity of the vein is less reliable, because normal veins can have artifactual low-level echoes and intraluminal clot can be hypoechoic or anechoic. Color Doppler US depicts venous thrombus as a filling defect or absence of flow.
Additional color Doppler features that can be assessed include spontaneous and phasic venous flow in response to augmentation. A venous waveform that lacks normal respiratory phasicity can indicate venous obstruction superior to that site. Similarly, compression of veins inferior to the vein being examined normally increases flow on spectral display. Lack of increased flow with augmentation indicates venous obstruction somewhere in between the site of compression and the Doppler site.