Venoplasty and stenting of the iliac vein are presently the “method of choice” in the treatment of femoro-ilio-caval chronic venous obstruction. The importance of venous outflow obstruction in the pathophysiology of chronic venous disorder has now been recognized, and it is apparent that reflux alone cannot explain the symptoms and signs of many patients. The iliac vein is the common outflow tract of the lower extremity, and chronic obstruction of this segment appears to result in more severe symptoms than does lower segmental blockage. Therefore, the femoro-ilio-caval venous segment has been the target area for balloon dilation and stenting.

Since it is not known at what degree of obstruction the venous flow is restricted, no tests are presently available for the accurate diagnosis of hemodynamically significant venous outflow blockage [9]. Commonly used routine noninvasive tests such as outflow air or strain-gauge plethysmographic tests and duplex Doppler ultrasound may indicate an outflow obstruction, but a normal test does not exclude significant ilio-caval blockage. Even invasive pressure tests are not sufficiently accurate. Presently, the diagnosis of outflow obstruction must ultimately be made by morphological investigations.

Ultrasound investigation should routinely be extended to involve the ilio-caval venous outflow and, in select cases with pertinent symptoms, be complemented by other morphological studies, if necessary. Varying investigations are used depending on local traditions. A single-plane transfemoral antegrade venogram has long been the routine morphologic investigation of the ilio-caval outflow. With the increasing awareness of the importance and anatomy of the non-thrombotic iliac vein lesions (compression lesions), this type of venogram is insufficient. Modern transfemoral venography should be performed using arteriographic techniques including subtraction, power injection of contrast dye, and multiple oblique imaging. Even multiplane venogram, however, may underestimate the severity and extent of the obstructive lesion as compared to direct imaging by IVUS. In a recent study of 100 patients, significant lesions (>50% area or diameter stenosis, webs, and/or collaterals) were found in 81% of the pelvic venous outflow with IVUS, while this was only found in 52% with multiplane venography in the same cohort [10]. IVUS is currently superior to any other imaging technique of venous ilio-caval outflow.

Although definition of a hemodynamically significant venous stenosis is lacking, a morphological obstruction of more than 50% stenosis has arbitrarily been chosen to be significant because of favorable clinical response when stented [11].

It is common to restrict venous workup of patients with chronic venous disease to a simple duplex Doppler ultrasound (DUS) of the lower extremity to below the inguinal ligament and then mainly for detection of reflux. A more aggressive approach toward diagnosis is warranted by extending the DUS to include the ilio-caval inflow and, if the findings are equivocal, consider performing additional morphological studies such as multiplane transfemoral venogram, computer tomography venography (CT-V) , magnetic resonance venography (MR-V) , or IVUS. There are no studies to demonstrate either the specificity or sensitivity of either CT-V or MR-V when compared to venography or IVUS. CT-V has the advantage of allowing either direct or indirect access of the venous system and is able to delineate the anatomy in extreme detail. CT-V is however compromised by the need for large radiation doses in what is predominantly a young and female population group. The routine use of CT-V therefore needs to be balanced against the cumulative radiation dose that these patients will experience. MR-V can be performed using either contrast or non-contrast techniques [12–15]. MR is less readily available, but the improvement in technology and development of improved sequences allow for excellent visualization of webs and trabeculations in the iliac and common femoral veins in particular [16, 17]. MR has reduced sensitivity in both the IVC and below the profunda/femoral vein confluence. The major advantage of MR is the absence of radiation; however this is compromised by reduced availability and long sequence times to allow for image acquisition. New techniques have also been developed that show promise for clot aging with MR targeted specifically at the fibrinogen component of acute clot. This may allow for better patient selection prior to commencing lysis [18]. In our practice, IVUS is used generously in symptomatic patients with morphological findings of stenosis or visualization of collaterals, which can be considered an indicator of obstruction, or when plethysmographic or pressure tests are positive for obstruction. Symptoms may range from painful swelling to severe stages with lipodermatosclerosis or ulcer. Patients of special interest are those with symptoms (especially pain) out of proportion to detectable pathology or those with typical symptoms but no detectable lesions on standard tests, those with no improvement of symptoms after standard treatment, and those with previous deep vein thrombosis.

The IVUS can also detect varying degrees of echogenicity in intraluminal masses, the vessel wall, and the surrounding tissue. Increased echogenicity of the vessel wall may indicate increased fibrosis and wall thickness often seen in postthrombotic veins. Varying echogenicity of intraluminal thrombi may correlate with the age of the thrombus. Fresh thrombus appears more translucent than old and is surrounded by inflammatory edema (Fig. 45.6). This may allow age determination of different parts of an extensive deep vein thrombus. Compliance of the venous wall is reflected by phasic movement during respiration. Lack of respiratory variations of the vein wall indicates less compliance with a stiffer wall. None of these observations are possible with venography. Contrarily, collateral formation is poorly shown by IVUS. Only axial collateral formation in close proximity to the native vein can be detected by IVUS. Venogram may occasionally fail to distinguish these from the main vein.

Arterial obstruction is usually due to thickening of the wall with plaque formation. Only rarely does outside compression play a major role. In the venous system, outside compression mainly by arterial structures appears to play a major role even in limbs with chronic ilio-caval postthrombotic obstruction (Fig. 45.7). These compression lesions (NIVLs) occur at the vessel crossings described in detail above. The relationship between NIVLs and acute iliofemoral DVT is well known [19]. A non-thrombotic iliac vein compression stenosis is rarely only focal when imaged by IVUS. The accompanying artery has an oblique course bilaterally at the common iliac veins causing a diffuse narrowing, although less, along the major length of the common iliac vein. Immediately above the internal-external iliac vein confluence, the common iliac vein becomes rounded and uncompressed. This is an important reference site to choose stent diameter in patients with NIVLs. In addition, 46% of the limbs with compression disease have been shown by IVUS to have stenosis beyond the common iliac vein [20]. Although this lesion is classically described to occur in the left iliac vein in younger females, it is not an uncommon finding in males, in elderly patients, and in the outflow of the right limb [20]. On venogram such a compression may be indirectly suggested by showing a widening of the iliac vein, a “thinning” of the contrast dye resulting in a translucence of the area, and the presence of transpelvic collaterals, sometimes despite a normal appearance of the iliofemoral vein (Fig. 45.8). With IVUS the compressed vein can be clearly delineated between the overriding artery and the posterior bone structure. This compression results in an hourglass deformity of the vein of varying degrees with frequently observed secondary intraluminal lesions such as web formation. IVUS investigation in 16 limbs with iliac compression syndrome showed that the iliac vein compression extended distally, involving the external iliac or common femoral veins in 68% (11/16). A filling defect representing thrombi was identified in 25% (4/16), and synechia in the compressed vein lumen was seen in 44% (7/16). These additional findings on IVUS led to modification of the intervention in 50% of limbs [5].