Venography uses a radiographic material injected into a vein on the top of the foot. The material mixes with blood and flows toward the heart. An X-ray of the leg and pelvis will then show the calf and thigh veins and reveal any blockages.
Although venography is very accurate and can detect blockages in both the thigh and the calf, it is also costly and cannot be repeated often. In addition, the injected material may actually contribute to the creation of thrombi. Therefore it is not often used.
Duplex ultrasonography can also be very accurate in identifying clogged veins. Projected sound waves bounce off structures in the leg and create images that reveal abnormalities. The addition of color Doppler imaging improves accuracy.
This test is noninvasive and painless, requires no radiation, can be repeated regularly, and can reveal other causes for symptoms. It also costs substantially less than venography. However, it is technically demanding and requires a skilled, experienced operator to obtain the most accurate results.
Ultrasonography is less sensitive in detecting thrombi in the calf and it has limited ability to directly image the deep veins of the pelvis.
Magnetic Resonance Imaging
Magnetic resonance imaging is particularly effective in diagnosing DVT in the pelvis, and as effective as venography in diagnosing DVT in the thigh. This technique is being increasingly used because it is noninvasive and allows simultaneous visualization of both legs.
However, an MRI is expensive, not always readily available, and cannot be used if the patient has certain implants, such as a pacemaker. In addition, the patient can experience claustrophobia.
The risk of developing DVT extends for at least three months after joint replacement surgery. The risk is greatest two to five days after surgery; a second peak development period occurs about 10 days after surgery, after most patients have been discharged from the hospital. In general, risk is greatest in the first 30 days after surgery.
Treatment is the same for both asymptomatic and symptomatic venous thromboembolisms. If the clot is located in the femoropoliteal vein of the thigh, treatment consists of bed rest and heparin therapy, followed by six months of warfarin. A clot in the calf veins does not normally require heparin treatment; outpatient warfarin treatment for six to 12 weeks is sufficient. These treatment regimens are designed to prevent the occurrence of a fatal pulmonary embolism and reduce the morbidity associated with DVT.