Venous Vascularization and Inflammation on Contrast-enhanced Ultrasound (CEUS) in Patients With Thrombosis

Background:

Contrast-enhanced ultrasound (CEUS) provides direct in-vivo visualization of the adventitial vasa vasorum using the fact that contrast agents microspheres are ideal intravascular tracers, thus, permitting a non-invasive assessment of the dynamic spatial and temporal heterogeneity of the microvasculature. Moreover, late phase CEUS has shown to detect inflammation by visualizing untargeted microbubbles phagocytosed by monocytes. The inflammatory process of the vessel wall and surrounding tissue associated with perivascular angiogenesis at the time of deep venous thrombosis (DVT) and superficial vein thrombophlebitis (SVT) may promote destruction of venous valves, valvular reflux and subsequent development of post-thrombotic syndrome (PTS). Therefore, in this study, the investigators will test the value of CEUS to detect venous perivascular vascularization and inflammation in patients with acute DVT or SVT.

Aims:

To determine the presence and degree of venous perivascular vascularization and inflammation assessed with CEUS in patients with acute DVT or SVT, and compare this to controls without thrombosis.

Patients and Methods:

20 patients with first unilateral proximal DVT and 10 patients with SVT of the lower-extremity will be included in this study. As control, 10 volunteers without DVT or SVT, and without history of thromboembolism, will be recruited. Diagnosis of DVT and SVT will be performed using standard compression and duplex ultrasound using a Philips (Bothel, WA) ultrasound scanner (iU22) equipped with a linear array L9-4 megahertz (MHz) probe. For CEUS imaging 2.5ml of SonoVueTM (Bracco spa, Milan, Italy) will be injected as an intravenous bolus into an antecubital vein. The thrombotic popliteal vein and the normal popliteal vein at the contralateral side or the thrombotic superficial vein and the normal superficial vein at the contralateral side will be evaluated using a standardized cross-sectional view. Similarly the normal popliteal vein and the superficial vein in a control group will be evaluated. Perivascular contrast-enhancement will be determined with visual interpretation (absent, moderate, abundant) and with quantitative analysis using a dedicated QLAB software (Philips; Bothel, WA) to quantify video intensity within the first minute after bolus contrast injection (perivascular vascularization) and at 6 minutes following the bolus contrast injection (inflammation). Visual based and quantitative analysis of perivascular contrast-enhancement in DVT or SVT will be compared to the contrast-enhancement at the non affected contralateral side and to results of the control group. CEUS imaging with quantification of perivascular contrast-enhancement will be performed at baseline, 2 weeks, and 3 months after acute thrombosis or initial investigation in controls. Additionally, at each visit, measurement of inflammatory markers (MCP-1, IL-6, IL-8, VCAM-1, vWF, and CRP), as well as quantitative measurement of leg volume using an automated 3D image system (Bauerfeind®, Zeulenroda-Triebes, Germany) will be performed.

Expected results:

The investigators hypothesize that venous perivascular vascularization and inflammation assessed by contrast agent enhancement can be quantified and will be significantly more pronounced in the perivascular tissue of the thrombotic vein than in the non affected vein and in controls, and will correlate with level of inflammatory markers and leg volume. Vascularization and inflammation will decrease during the process of thrombus resolution from baseline to 3 months follow-up.

Significance:

These results would provide new information on the pathophysiological concept of thrombosis and thrombus resolution. It might help to better understand the pathophysiologic mechanisms that promote the development of chronic venous insufficiency and post-thrombotic syndrome. As inflammation with pronounced perivascular vascularization might play an important role in incomplete thrombus clearance, venous outflow obstruction and the development of post-thrombotic syndrome after acute DVT, in the future, our results could lead to novel approaches to interrupt the natural history and prevent post-thrombotic syndrome.