20. Imaging of the venous and lymphatic system and their diseases. Deep vein thrombosis.

Venography

Venography refers to any imaging technique which allows for visualisation of veins. The equivalent for arteries is called angiography, and both can be performed during the same procedure. Venography can be performed with CT or MR. Duplex ultrasonography is also used to visualise veins, but this isn't referred to as venography.

CT venography

CT venography involves using iodine contrast to visualise veins. This is usually indicated for:

• Cerebral venous thrombosis
• Venous thromboembolism
  • DVTs where ultrasound can't visualise
• Superior vena cava syndrome
• Vascular malformations

MR venography

MR may also be used for venography, mostly for the same indications as CT if iodine contrast is contraindicated.

Deep vein thrombosis

Deep vein thrombosis (DVT) is a form of venous thromboembolism which occurs in deep veins, most commonly in the legs or groin. Its main importance is the risk of the deep venous thrombosis dislodging and traveling to the lungs, causing pulmonary embolism (PE). DVT mostly affects the distal deep veins, but may affect the larger, proximal veins as well, including the iliac, femoral, or popliteal veins. PE is a serious complication which can lead to death in 30 – 60% of cases, and is more common in case of proximal DVT.

Imaging

Ultrasound is important in the evaluation of DVT, and is the first choice. When applying pressure to the vein with the ultrasound probe and the vein is not completely compressible, a thrombus is lodged in the vein. Examining in this manner is called compression Doppler ultrasound. Ultrasound may also rarely show the thrombus as a hyperechoic mass in the venous lumen. Doppler imaging may show absent blood flow. If any of these findings are present, the diagnosis of DVT is made.

If D-dimer and ultrasound are inconclusive, venography with CT or MRI may be used.