Deep vein thrombosis (DVT) and its complications continue to be a common problem in the United States. Estimates range from 200,000 to 250,000 annual cases of DVT in the United States. Not only is DVT common and potentially life threatening, but it is also difficult to diagnose clinically. Some estimate that up to 50% of untreated DVT patients go on to develop pulmonary embolism, and without treatment, PE is associated with a mortality rate of approximately 30% leading to nearly 50,000 deaths per year.
With the difficulty in diagnosing DVT clinically, compression ultrasound (US) is an extremely valuable tool. Compression ultrasound is highly sensitive and specific for the detection of deep vein thrombosis in the upper leg with values of 93% and 98% respectively. MR Venography is a gold standard equivalent with sensitivity and specificity of 100%. While, CT Venography has sensitivities ranging from 89%-100%, and specificities ranging from 94-100%.
Doppler compression ultrasound with real-time, B-mode imaging is used at most locations. The biggest strengths of this modality include safety, availability, reliability, and its noninvasive nature. Its biggest benefit comes from the detection of acute symptomatic proximal DVT, as well as DVT of the upper extremities while still being able to identify other pathologies. However, compression ultrasound is not specific or sensitive for the detection of DVT in patients with asymptomatic proximal DVT or in patients with symptomatic or asymptomatic DVT of the calf, and it demonstrates limited accuracy in cases of chronic DVT. Therefore, direct US examination of the calf veins is only performed if there are indirect indications of DVT below the knee. US is less sensitive for detecting thromboses in the deep veins of the calf because it is not always possible to visualize all three of the major veins in this region. If clinical suspicion remains high, US examination should be repeated after a week because of the danger of thrombus propagation into the thigh veins.
The primary diagnostic criterion for DVT using compression ultrasound is noncompressibility of a vein. Secondary diagnostic criteria include the visualization of an echogenic thrombus within the vein lumen, venous distention, complete absence of spectral or color Doppler signal from the vein lumen, and loss of flow phasicity, response to Valsalva or augmentation. The last US techniques mentioned give indirect evidence of thromboses above and below the site of examination.
Lastly, acute and chronic deep venous thrombosis have slightly different compression ultrasound characteristics. In acute DVT the thrombus is hypoechoic and occasionally anechoic, the vein lumen size is distended, the compressibility is spongy, and collateral veins are normally absent. In chronic DVT the thrombus is echogenic, the vein lumen is narrow and irregular, the compressibility is rigid and incompressible, and collateral veins are often present.