Ultrasound of the deep veins of the lower extremities

The deep veins of the lower limb are accompanied by arteries of the same name. Usually, the veins below the knee joint are paired. To demonstrate the anterior tibial veins, place the transducer on the palpable anterior tibial muscle lateral to the anterior border of the tibia. The anterior tibial vein is located posterior to the extensor muscles and slightly anterior to the interosseous membrane. Inexperienced physicians often scan too deeply. The interosseous edges of the tibia and fibula indicate the level of the interosseous membrane, which can be directly visualized using ultrasound.

The posterior tibial and peroneal veins are located in the flexor region between the triceps and deep flexors. Bone landmarks are used for guidance: when the leg is held in a neutral position, the posterior surface of the tibia is anterior to the posterior surface of the fibula. The posterior tibial veins are located centrally on the posterior surface of the tibia, while the peroneal veins are very close to the fibula.

The popliteal vein is referenced by the artery of the same name, which runs in front of it. The vein is easy to find due to its large caliber and superficial location. Even light pressure with the sensor often allows you to completely compress the vein, and its image disappears. The popliteal vein is paired in 20% of cases and triple in 2%. The femoral vein lies behind the artery in the adductor canal, located medial to the artery at a more proximal level. The iliac vein runs posteriorly and medial to the artery of the same name. The deep femoral vein flows into the superficial vein at a distance of 4-12 cm below the inguinal ligament. It runs in front of the artery of the same name. The superficial femoral vein is paired in about 20% of cases, and three or more veins are found in 14% of cases.

Examination for thrombosis

The most accessible ultrasound technique for diagnosing deep vein thrombosis of the lower extremities is a compression test, which can be performed from the groin to the ankles. The color mode is used only for guidance, since the vessels are easier to visualize. If the quality of the B-mode is good, there is no need to use the color mode for the compression test. The key criterion is not “color squeezing”, but full compressibility of the vascular lumen. If the image in B-mode is of poor quality, the color mode should be used and, if necessary, combined with distal compression.

The most elegant compression test involves rocking the hand holding the transducer. The increased blood flow allows the examiner to identify the vein and ensure that it is at least partially patent. The hand is then advanced, pressing on the transducer. No blood flow is detected in these veins during the non-compression examination. With distal compression, the blood flow accelerates. The transducer is then fully compressed. Only the venous segment that is compressed can be accurately assessed. Several transverse images should be obtained over the full length of each of the lower limb veins (common femoral, superficial femoral, deep femoral, popliteal, anterior tibial, posterior tibial, and peroneal veins) using variable compression.

In most cases, the iliac veins cannot be compressed due to the lack of dense underlying tissue, so the assessment is performed in color mode.

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Survey methodology

For duplex scanning of the veins of the lower limb, the patient is positioned supine, with the upper end of the body slightly elevated. Begin the examination from the inguinal region with a 4-7 MHz linear transducer. Trace the femoral vein distally from the femoral epicondyle with variable compression. Also note the course of the deep femoral vein. Move down the limb and scan the anterior tibial veins, then turn the patient prone. A small cushion is placed to gently flex the knee. Bring out the popliteal vein in cross-section. First, trace the vessel proximally, then apply variable compression (often the distal part of the adductor canal is better visualized from the posterior approach than from the anterior one). Next, trace the vessels distally and separately evaluate the posterior peroneal and tibial veins.

Be careful when examining the proximal fibular veins. Because of their physiological dilation and normal skin tension over the head of the fibula, use strong and often painful pressure to compress these veins. The specialist's conclusion depends on the data obtained at this point and on the clinical symptoms. Make a conclusion either on the examination of the common femoral vein while the patient is performing the Valsalva maneuver, or on the data of color scanning of the iliac veins using a 4-7 MHz convex probe.

If you are unable to adequately assess the veins of the lower leg using this standard protocol, try bending your knee and resting your lower leg over the edge of a table or bed. Support the lower leg with your left hand and scan with your right. The increased hydrostatic pressure will result in better filling of the veins, allowing for better identification. On the other hand, color scanning is impaired due to the slower blood flow and the need for greater force to compress the veins than in the supine position.