Ultrasound elastography for the age determination of venous thrombi. Evaluation in an animal model of venous thrombosis.

The exact age determination of venous thrombi is important if thrombolytic therapy or surgical thrombectomy is considered. Clinical symptoms as well as duplex-ultrasound and phlebography are unreliable in this respect and do not allow an exact age estimation. Ultrasound elastography can provide information about the elastic properties of thrombi. Since thrombus elasticity decreases with age due to the organisation process, it should be possible to use elastography to stage the degree of organisation and thereby determine the age of venous thrombi. Experimental venous thrombi aging 1, 3, 6, 9, 12 and 15 days were created in a porcine model by laparoscopic ligation of the infrarenal Vena cava in combination with transfemoral infusion of thrombin. The thrombosed iliac veins were explanted and embedded in gelatine, after that they underwent examination by ultrasound elastography. In addition, histological evaluation of the thrombi was performed. Elastography demonstrated a decline in thrombus elasticity between days 6 and 12 with the 12-day-old thrombi being about 3 times harder then the 6-day-old thrombi. This correlated with the histological findings, which demonstrated a marked increase in fibroblast and collagen production in the clots during this time, with the 12- and 15-day thrombi showing signs of advanced organisation. In conclusion, in an experimental setting, ultrasound elastography was helpful in determining the exact age of venous thrombi. The differences in elasticity were most pronounced between days 6 and 12, which is also the most relevant time frame when considering invasive therapies in human venous thrombosis.