13.5 Iliocaval Duplex and Venous Stent Assessment

Why a leg study may not answer a pelvic question

Iliocaval duplex evaluates the iliac veins and inferior vena cava (IVC). It is relevant to unexplained limb swelling, suspected proximal thrombosis, chronic venous obstruction, and postoperative venous stent assessment. A compressible femoral or popliteal vein does not exclude pelvic obstruction. Conversely, an abnormal common femoral waveform is an indirect clue; it does not locate or grade an iliac lesion by itself.

Review symptom laterality, onset, prior DVT, cancer, pelvic surgery, pregnancy where relevant, venous interventions, and anticoagulant history. Determine whether the question concerns a native vein, chronic post-thrombotic obstruction, nonthrombotic compression, or a stent. Record the stent location and prior reconstruction if available. Compare with the most recent technically useful study rather than a summary stating only “patent.”

Anatomy and preparation

The common iliac veins join to form the IVC, which typically lies to the right of the aorta. The left common iliac vein passes beneath the right common iliac artery. This relationship can produce anatomic compression, but compression alone is not synonymous with May-Thurner syndrome. The syndrome requires a compatible clinical problem and evidence supporting a clinically important outflow lesion. Many asymptomatic people have some degree of venous narrowing.

Use a low-frequency curvilinear transducer for deep pelvic and abdominal segments, changing to a higher-frequency probe for superficial distal segments when helpful. Fasting may reduce bowel gas when appropriate, but should not delay urgent assessment or conflict with the patient's medical needs. Supine positioning, lateral approaches, and gentle repositioning can improve access. Explain the examination and protect privacy during groin imaging.

A complete acquisition approach

1. Obtain bilateral common femoral venous spectral waveforms under comparable breathing conditions.
2. Follow the external iliac veins as far proximally as accessible.
3. Identify the common iliac veins, confluence, and accessible IVC.
4. Assess grayscale lumen, color filling, spontaneous flow, phasicity, and focal changes in velocity.
5. Image collateral pathways and suspected thrombus or extrinsic compression.
6. For a stent, evaluate inflow, complete visible stent length, overlap zones, both ends, and outflow.

Deep pelvic veins cannot usually be compressed directly. Evaluate the visible lumen with grayscale, color, and spectral Doppler together. Set the scale and filter for slow venous flow and adjust gain without introducing color blooming. A large depth and bowel gas may prevent visualization; document that limitation. Failure to see a segment is not proof of thrombosis.

Interpreting native iliocaval findings

Acute thrombosis may produce luminal expansion, intraluminal material, and absent or reduced flow. Chronic post-thrombotic disease can produce irregular walls, fibrous channels, narrowed caliber, and collateralization. Echogenicity alone does not determine age. Report acute-appearing thrombosis, chronic post-thrombotic change, or indeterminate findings according to the integrated appearance and clinical context.

Proximal obstruction can dampen respiratory and cardiac transmission in the common femoral vein. Unilateral continuous flow compared with a normally phasic opposite side raises suspicion for an ipsilateral proximal lesion. Bilateral abnormalities broaden the differential to the IVC, bilateral lesions, and systemic or respiratory influences. Breath-holding, ventilatory support, body position, and acquisition technique affect waveform appearance.

Venous stents

Trace the stent from its distal inflow to its proximal outflow. Confirm that color fills the visible lumen and obtain spectral samples at representative locations. Look for intraluminal material, focal edge narrowing, overlap abnormalities, external compression, and inflow disease. A stent may be patent yet function poorly because the veins feeding it are severely diseased. The examination must therefore extend beyond the metal framework.

Use validated venous stent criteria and serial comparison rather than importing arterial PSV ratios. Venous flow varies with respiration, hydration, posture, and central pressure. A focal velocity increase with visible narrowing is more persuasive than one isolated number. Loss of flow, new intraluminal thrombus, progressive narrowing, or new severe swelling should prompt timely communication and assessment by the treating team.

Worked cases

A patient has left-leg swelling and a compressible femoropopliteal system. The left common femoral waveform is continuous while the right is phasic. A pelvic view is obscured by gas. The correct preliminary finding is a technically limited pelvic evaluation with indirect evidence concerning for left proximal obstruction. “No DVT anywhere” would overstate the examination. The interpreting physician may recommend additional imaging based on the urgency and clinical question.

In a second case, a previously stented left iliac vein shows new material occupying the distal lumen and markedly reduced flow compared with baseline. Check the accessible inflow veins and stent ends, preserve representative images, and communicate the suspected complication promptly. Do not manipulate the patient or scan indefinitely while delaying notification of a clinically important new obstruction.

Correlation and reporting

CT venography and MR venography provide additional anatomic information, with modality-specific contrast, renal, implant, and artifact considerations. Catheter venography and intravascular ultrasound (IVUS) may be used by specialists during invasive assessment. Duplex cannot substitute for every function of these modalities, particularly when pelvic visualization is incomplete.

The report should name the vessels and stent segments assessed, state patency and observed pathology, distinguish direct from indirect evidence, compare with prior studies, and identify unseen segments. Document whom you notified, the time, and the preliminary nature of your communication. This produces an actionable examination without converting suggestive hemodynamics into an unsupported definitive diagnosis.

CCI RVS abdominal/visceral task list and IAC Vascular Testing standards — checked October 18, 2026.