Contrast Venography

Michael A. Ricci, MD, RVT

Venography has often been touted as the "gold standard" in the diagnosis of acute deep venous thrombosis although its use has been largely supplanted of late by Duplex ultrasound scanning. Nonetheless, contrast venography still has a role when other methods are impractical or equivocal or in complicated clinical situations. Venography remains the best technique to thoroughly define the venous anatomy.

Technique
The technique of ascending venography was first described in 1923 and remains largely unchanged although a number of modifications have been introduced. The test starts with dye injection into a needle in the veins of the foot with the patient on a tilt table. Injection usually starts in the upright position and usually includes a tourniquet to prevent flow into the superficial veins and direct dye into the deep venous system. Newer digital imaging techniques in conjunction with conventional films can result in lower dye loads.

Occasionally, descending venography may be useful to define proximal venous valvular incompetence. This is commonly performed in a manner similar to arteriography with guidewires directed from the opposite limb and placement of an injection catheter in the iliac veins. With the patient upright dye is introduced and flows down to a level at which competent valves are encountered. This test is usually used as a prelude to venous reconstruction rather than to diagnose acute deep venous thrombosis.

Complications
Although pain from the needle as well as the dye injection are common, serious complications are primarily related to the contrast media. The most immediate and serious complication is anaphylaxis as a reaction to the contrast injection, although this is fortunately a rare occurrence. Extravasation of contrast may cause pain. The contrast agent, itself, may induce a thrombosis in up to 5% of cases. Precautions such as flushing of the veins with saline after injection and early ambulation may minimize this risk.

Interpretation
The most reliable sign of venous thrombosis is a filling defect or so-called "railroad track sign", with contrast outlining the clot. Non-filling of a vein or even of the entire deep venous system, diversion of flow, or the presence of collateral veins are not, in themselves, diagnostic, but may be taken to indicate deep venous thrombosis in the right clinical setting. Even technically superior studies, however, may not fill the iliac veins 18% of the time so some caution in interpretation is required.