Deep Vein Thrombosis: Venography, Endovascular Diagnosis and Treatment

Overview

Deep vein thrombosis (DVT) represents a significant source of morbidity due to acute symptoms, risk of pulmonary embolism (PE), and long-term sequelae including post-thrombotic syndrome (PTS). The radiologist's role spans both diagnosis - primarily through ultrasound and, where indicated, catheter venography - and therapeutic intervention, including catheter-directed thrombolysis (CDT), pharmacomechanical thrombectomy (PCDT), balloon angioplasty, and venous stent placement. These notes focus on the interventional aspects within the context of the RANZCR Part 2 examination, covering diagnostic catheter venography and venous endovascular therapeutics.

Diagnostic Catheter Venography

Indications

Contraindications

Limitations

• Catheter venography provides a 2-dimensional luminogram and may underestimate external compression or intramural pathology.
• Intravascular ultrasound (IVUS) is significantly more sensitive and specific than conventional venography for identifying non-thrombotic iliac vein lesions (e.g., May-Thurner compression), wall-adherent chronic thrombus, and post-lytic residual stenoses. IVUS is also valuable for assessing luminal patency after treatment and guiding stent placement.
• Cross-sectional imaging (CT venography, MR venography) is preferred for assessing iliac vein and IVC anatomy, identifying extrinsic causative pathology (pelvic malignancy, retroperitoneal disease), and planning intervention.
• Radiation exposure and invasive access are disadvantages compared with non-invasive modalities.

Procedural Complications

Imaging Assessment for DVT: Modality Summary

Therapeutic Endovascular Management of DVT

Indications for Endovascular Treatment

Endovascular treatment (CDT, PCDT, mechanical thrombectomy ± stenting) is now focused on iliofemoral DVT (iliac veins and/or IVC involvement):

• Acute iliofemoral DVT with significant symptom burden (limb-threatening phlegmasia or severe oedema)
• Prevention of PTS in selected patients with acute proximal DVT
• Symptomatic chronic iliofemoral occlusion with debilitating venous claudication or severe chronic venous insufficiency
• May-Thurner syndrome with associated thrombosis

Critical evidence-based limitation: Randomised trial data (including the ATTRACT trial) demonstrated a trend towards lower PTS rates at 2 years in the iliofemoral subgroup but the trial was not adequately powered to confirm this. As a result, endovascular treatment of DVT isolated to the femoropopliteal veins is no longer performed. Intervention remains indicated for DVT involving the iliac veins and/or IVC.

Access for Endovascular DVT Treatment

• If patent, the popliteal or femoral vein is used for access.
• If the popliteal vein is thrombosed, one of the paired posterior tibial veins (at the calf or ankle) is preferred.
• Internal jugular vein access is an option but traversing valves in a retrograde direction can be challenging.
• Thrombus is crossed using a 0.035-inch hydrophilic wire; venography is then performed to determine location and extent.

CDT Technique

• A multiside-hole infusion catheter is placed into the thrombosed segment.
• Recombinant tPA is the most commonly used thrombolytic agent (rate: 0.5-1.0 mg/hour); no lytic agent currently has FDA approval for this indication.
• Infusion duration: 6-24 hours for CDT alone; pharmacomechanical thrombectomy (PCDT) achieves thrombus clearance over a much shorter time.
• Monitoring during infusion: full blood count, aPTT, and fibrinogen every 6 hours; clinical signs of bleeding (epistaxis, access site oozing) prompt dose reduction or cessation.
• Patients must be monitored in a step-down unit or ICU during infusion due to haemorrhage risk.
• After thrombus removal, completion venography is performed; residual thrombus is treated with balloon maceration or mechanical thrombectomy; obstructive lesions are treated with balloon angioplasty ± stent placement.

Contraindications to Catheter-Directed Thrombolysis

Multidisciplinary risk-benefit assessment is essential. Haemorrhage - mainly at the access site - occurs in up to 30% of thrombolysis cases.

Balloon Angioplasty and Stent Placement for Venous Disease

Principles

Balloon angioplasty refers to percutaneous transluminal treatment of a venous stenosis or occlusion using an inflatable balloon catheter advanced under fluoroscopic guidance. Following thrombus clearance, residual obstructive lesions - post-lytic stenoses, extrinsic compressions (e.g., May-Thurner), or chronic occlusive webs - are identified by venography and IVUS, then treated with angioplasty and, where appropriate, stent placement.

In May-Thurner syndrome (left common iliac vein compression), the filling defect is visible on conventional venography but IVUS is more sensitive and specific for identification. When the lesion correlates with symptoms, treatment with angioplasty and stent placement is performed. When not associated with venous thrombosis, treatment is relatively straightforward; in the presence of thrombosis, CDT or PCDT is required first.

Indications for Balloon Angioplasty ± Stenting in Venous Disease

Key stenting principle: Stenting is reserved for iliac vein segments and, when necessary, the common femoral vein (stent may extend caudally to the level of the lesser trochanter of the femur as the landmark). Stents should not be placed routinely in the femoropopliteal veins; angioplasty alone is the treatment of choice for chronically occluded femoropopliteal veins given poor stent performance in this territory.

IVC Filter Retrieval During Recanalization

When IVC recanalization is planned in the presence of a filter, the ongoing need for caval filtration must be assessed. If no longer required, retrieval during the same session should be considered. Planning should account for: filter type, indwelling duration (fracture risk with longer periods), position, wall penetration, and retrieval hook accessibility. Tilting or embedding of the hook increases retrieval difficulty.

Contraindications to Venous Stenting

• Active untreated sepsis
• Uncorrected coagulopathy
• Anatomy unsuitable for stent deployment
• Absence of symptoms attributable to venous obstruction
• Inability to comply with anticoagulation/antiplatelet therapy

Procedural Complications

Post-Procedure Imaging Appearances

• Completion venography: stent fully expanded with no residual waist; good runoff to IVC.
• IVUS: confirms luminal dimensions and stent apposition.
• Duplex ultrasound: primary surveillance tool at follow-up (typically 1, 6, and 12 months, then annually).
• CT venography: used for complex cases where ultrasound is inconclusive; assesses stent position, patency, and in-stent restenosis.
• Recurrent symptoms should prompt re-imaging.

Interpretation and Reporting for Venous Angioplasty/Stent

A structured report should include: 1. Indication and relevant clinical context 2. Access site and approach 3. Initial venographic findings: extent and location of thrombus or stenosis 4. Procedure performed: CDT duration, pharmacomechanical device used, balloon size and pressure 5. Stent details: type, size (diameter × length), location, landmarks used (e.g., lesser trochanter for distal extent) 6. Post-procedure venographic result: patency, residual stenosis (as percentage), flow pattern, runoff to IVC 7. Complications: none / specify 8. Anticoagulation plan: post-procedure anticoagulation guidance

Endovascular Aneurysm Repair (EVAR)

Principles

EVAR involves placement of a covered stent-graft (fabric-covered metallic frame) within an aneurysmal segment of the aorta to exclude the sac from arterial pressure, thereby preventing rupture. First described in 1991, EVAR is now the dominant approach for elective infrarenal AAA where anatomy is suitable, with lower short-term mortality than open repair. The principal aim of stent-grafting is to line the inside of the vessel; accurate positioning is paramount. Endovascular repair should be carried out by experienced staff in a sterile environment of theatre standard with optimal imaging facilities, capacity for rapid conversion to open repair, and ICU/HDU postoperative care available.

Delivery systems range from 14 to 25 F (approximately 4-9 mm) in diameter. Patients with access vessels narrower than the delivery system require adjunctive procedures (angioplasty, stenting, or "pave and crack" deliberate over-dilation).

There are two main stent types: - Balloon-expandable: mounted on a balloon catheter, deployed by balloon inflation; precise placement. - Self-expanding: deployed by sheath retraction, exert ongoing radial force; "windsock" effect of systolic pressure during deployment may displace the device distally, particularly in the thoracic aorta.

Indications

Open surgical mortality rates for reference: elective thoracic ~8%, elective abdominal ~5%.

Anatomical Prerequisites and Contraindications

Proximal neck (critical for efficacy): - Length $\geq 15$ mm infrarenal - Diameter typically $\leq 32$ mm - Angulation $< 60°$ between suprarenal aorta and neck; $< 60°$ between neck and aneurysm - Absence of significant circumferential thrombus or calcification at neck - Absence of conical, barrel, or severely tapered neck morphology

Adverse anatomy (relative contraindications):

Where anatomy is hostile, advanced techniques (fenestrated EVAR, chimney/parallel stent-grafts - e.g., CHEVAR) may be employed, but carry additional risk (e.g., type 1 endoleak via guttering alongside parallel grafts).

Perioperative Considerations

• Formal cardiopulmonary fitness assessment (e.g., CPET) and MDT discussion before elective repair.
• Imaging: CT angiography for morphological assessment; cone-beam CT (CBCT) provides valuable on-table information during complex procedures.
• CO₂ or gadolinium angiography available for patients with contrast allergy or at risk of contrast-induced nephropathy.
• For critical proximal positioning (short/angulated necks): overdrive cardiac pacing or pharmacological blood pressure reduction may be used during deployment to counteract the windsock effect.
• Once fully released, a stent-graft cannot be retrieved or repositioned without open surgery.

Post-Procedure Imaging Appearances - Normal

• Immediate post-procedure: Stent-graft fully deployed and expanded; no contrast outside graft lumen; normal perfusion of renal and visceral arteries.
• Aneurysm sac: Expected to remain stable or decrease in diameter (sac regression = successful exclusion).
• Limb patency: Both iliac limbs patent without kinking.
• EVAS (endovascular sac anchoring system) - specific appearance: Homogeneous high density within the endobag immediately post-procedure is normal (not endoleak); density reduces over time to become isodense with the surrounding sac.
• Surveillance CTA typically at 1 month, 12 months, and annually thereafter.

Endoleak Classification and Management

Endoleak - blood flow within the aneurysm sac outside the stent-graft - is the most important EVAR-specific complication:

CT technique: Dual-phase or delayed-phase CTA is essential - arterial phase identifies type 1 and 3; delayed phase is more sensitive for type 2. CEUS and power Doppler ultrasound are radiation-free surveillance alternatives with good sensitivity for endoleak detection (including type 2 from IMA or lumbar arteries).

Other EVAR Complications

Air in the sac: Expected immediately post-procedure; persistent or new air on delayed imaging raises infection concern.

Systematic Approach to Reporting EVAR Surveillance CTA

A structured EVAR surveillance report should include:

1. Aneurysm sac diameter: Maximum diameter in axial and coronal planes; compare with all prior studies
2. Endoleak: Present/absent; classify type; quantify sac enhancement; compare sac size trend
3. Graft position: Proximal extent relative to renal arteries; distance from lowest renal artery to graft top
4. Limb patency: Both iliac limbs; any kink, stenosis, or occlusion
5. Device integrity: No fracture, disconnection, or migration
6. Visceral/renal arteries: Patent and uncovered
7. Access vessels: Iliac/femoral arteries - any aneurysm, stenosis, or new pathology
8. Aneurysm wall: Calcification pattern; mural thrombus changes
9. Adjacent structures: Signs of infection, fistula, or retroperitoneal haematoma

Key Pitfalls and Errors

Summary Table: DVT Interventional Eligibility