In experienced hands, duplex ultrasonography (US) provides extremely sensitive and specific information regarding the chronicity and extent of infrainguinal venous obstruction. Diagnostic accuracy in the iliocaval venous system is less predictable due to the presence of overlying bowel gas and abdominal adiposity.

Duplex-derived criteria for acute venous occlusion include incompressibility under direct vision, partial luminal obstruction within the normally echo-free lumen, and absent or abnormal venous flow characteristics with respiration or following a Valsalva maneuver or distal compression.⁸

The primary advantages of duplex imaging include its noninvasive nature, avoidance of ionizing radiation or nephrotoxic contrast agents, easy reproducibility, portability, and accessibility in the outpatient setting. Additionally, substantial cost savings are realized compared to other imaging modalities. Other advantages include the ability of duplex scanning to differentiate hematomas, lymphatic system obstruction, superficial thrombophlebitis, and other soft tissue abnormalities from deep venous obstruction. Thus, duplex scanning is the initial imaging modality of choice in all patients with suspected iliofemoral DVT. When sufficient imaging parameters are met, definitive therapeutic intervention may be safely performed based on duplex-derived anatomic and diagnostic imaging alone.

CT phlebography is frequently ordered for assessment of limb swelling in the inpatient setting. Advantages of this modality include nearly universal availability day or night, less reliance on skill and experience of the technical staff performing the procedure, outstanding spatial resolution, reproducibility and sensitivity throughout the entire venous system, the simultaneous ability to image pulmonary arterial flow and lung perfusion, freedom from limb pain induced by direct probe compression during ultrasound examinations, and the ability to incidentally diagnose concurrent conditions (such as solid organ neoplasia) that may influence thrombogenicity or suitability for treatment with open versus endovascular techniques.

The modern helical CT phlebogram provides a diagnostic sensitivity and a specificity of nearly 100% per year and was found to detect previously unsuspected venous thrombosis at a prevalence of 1.1%.^9,10

CT phlebography also provides useful information regarding thrombus density (and thus chronicity), the presence of residual luminal patency in obstructed veins, and the nature and severity of extrinsic iliac vein compression when present.

The applicability of CT phlebography to the diagnosis of venous obstruction is limited by the volume of iodinated intravenous contrast required to obtain optimal spatial resolution in target vessels, as well as considerable whole-body radiation exposure inherent in CT imaging. On average, the radiation dosage delivered by diagnostic CT phlebography is equivalent to that of over 1,200 chest x-rays or over 10 years environmental exposure at sea level (dosage equivalents courtesy of Radiation Physics Department, Stanford Hospital & Clinics). This is particularly true in patients with reduced creatinine clearance, women of childbearing age who may be pregnant, or in children. For many reasons, including the considerable expense associated with the study, CT phlebography should not be considered a first-line study but rather reserved for patients in whom duplex scanning does not provide sufficient anatomic guidance or where additional diagnoses (e.g., pulmonary embolization, solid organ malignancy, or external iliac vein compression, etc.) merit evaluation or exclusion.

MR phlebography shares many of the advantages and disadvantages of CT-derived cross-sectional imaging, including the ability to obtain high-quality, high-resolution images of surrounding soft tissues and delineate the extent of accompanying lymphadenopathy, soft tissue sarcomas, venous aneurysms, malformations, and compression syndromes that may influence treatment and long-term management considerations. MR phlebography also provides a sensitivity and specificity of nearly 100%, respectively, in the diagnosis of acute iliofemoral venous occlusion.¹¹

However, unlike computed tomography venography (CTV), magnetic resonance venography (MRV) can be used during pregnancy and provide reduced risk of nephrotoxicity in patients with reduced creatinine clearance (although gadolinium is contraindicated in patients with an estimated glomerular filtration rate [eGFR] of more than 60 mL per minute).

Contraindications for MR-based venous imaging include the presence of implantable pacemakers/defibrillators/infusion systems or other ferromagnetic devices and surgical clips/endografts, as well as claustrophobia in affected patients. MR studies are also expensive compared to duplex US, and dedicated personnel and equipment are less widely available than are modern, multirow-detector CT imaging capabilities. Thus, MR phlebography is considered most appropriate as a secondary examination in the absence of suitable duplex imaging or in the presence of contraindications to CT phlebography. MR phlebography may be particularly useful in the evaluation of coexisting or complicating ipsilateral or central venous vascular malformations.

Despite continuing improvements in the quality and widespread availability of noninvasive imaging, catheter-based contrast phlebography remains the gold standard for iliofemoral venous evaluation. Sensitivity and specificity are also nearly 100%, and in addition to anatomic information, physiologic venous pressure and flow information are also provided throughout the iliocaval system when accessed in a retrograde fashion from the CFV.

Typical fluoroscopic findings include abrupt vessel cutoff in the case of total occlusion or visualization of a filling defect with residual luminal flow around the margins, a phenomenon known as “tram tracking.”

An obvious limitation is the relatively high degree of operator dependency, both in terms of physician and facility capabilities. Catheter-based contrast phlebography may be nondiagnostic in up to 18% of cases due to misinterpretations, artifacts, or superimposition of overlying structures.¹² Thus, experience and suitable infrastructure are necessary to ensure accuracy and precision.