Diagnosis of Thrombophlebitis
In the past, thrombophlebitis often was diagnosed using contrast venogram. The first step in performing a contrast venogram is to insert an IV into the foot, which can be difficult due to the structure of the veins. Then, while the patient is sitting upright, a warm towel is applied to the foot to make the veins easier to locate and to improve venous access.
After a small needle is inserted into a vein in the top of the foot, contrast material is injected and the veins in the calf and thigh are imaged. This test provides excellent images of the deep veins in the calf all the way up to the groin. Although blood clots cannot actually be seen, they are obvious as "filling defects" in the dye-filled vessels.
Contrast venography is still used to detect blood clots, but there are a couple of drawbacks, including the use of intravenous contrast and delivery of that contrast into the foot.
Ultrasound often is used to diagnose thrombophlebitis. In most people the large vein in the groin (common femoral vein) is just under the skin and is very easy to on ultrasound. The vein in back of the knee can also be imaged using ultrasound, although not quite as easily as the femoral vein. The 3 veins in the calf that come together to form the popliteal vein, are not easy to image using ultrasound because the veins often are difficult to find within the muscle.
There is some controversy as to whether or not ultrasound is enough. Some physicians feel that clots within the calf veins, which have not entered the popliteal vein, are clinically insignificant except for the pain they cause. Other physicians may insist on a contrast venogram if a clinical examination and the results of an ultrasound conflict.
During ultrasound, the radiologist looks for the appearance of the veins in the deep venous system. The focus is on the flow of blood inside the vein.
Normally, veins appear quiet and the flow appears slow next to rapidly pulsing arteries. The rapidly flowing blood in the arteries gives the inside of these vessels a smoky or cloudy appearance. The very slowly moving blood in the vein gives the inside of that vessel a very clear, watery appearance.
When a vein is compressed with an ultrasound transducer, it narrows more and more as the flow blocked and refills as the pressure is removed. If a Doppler sound signal is applied to the flowing blood in the lumen, a typical venous pulse is observed. If the last part of the extremity (below the vein) is squeezed, there is a noticeable effect on that vein as it enhances to accommodate the increased blood flow. Blood clots change all this by narrowing or occluding (blocking) the channel, so flowing blood is no longer visible on ultrasound. The solid clot prevents compression and since there is no flow in the vessel, there is no enhancement either.
Ultrasound may overlook an isolated clot. It also may be difficult to get reliable results in patients who have had previous episodes of thrombophlebitis in the same leg or who have chronic thrombophlebitis. Patients with a recent surgical wound in the knee or groin area are difficult to image because of skin contact problems.
Venous ultrasound in the lower extremities has been one of the great improvements in radiology over the past decade. Contrast venography is a test that most patients would rather not have to go through, and ultrasound is a completely noninvasive test that provides adequate information in most cases.