Overview
Definition:
An iliac conduit is a surgically created vascular graft or extension, typically an autologous vein or a synthetic tube, anastomosed to a healthy segment of the iliac artery
Its primary purpose in the context of complex Endovascular Aneurysm Repair (EVAR) is to provide a reliable and adequate proximal landing zone for the EVAR graft when the native iliac arteries are severely diseased, calcified, or tortuous, rendering standard EVAR deployment technically challenging or impossible
This technique effectively "reconstructs" a suitable proximal seal zone in otherwise unreconstructable anatomy
It is a hybrid approach combining open surgical principles with endovascular techniques.
Epidemiology:
The incidence of patients with abdominal aortic aneurysms (AAAs) requiring EVAR who also present with complex iliac anatomy (e.g., severe iliac stenosis, occlusion, extensive calcification, inadequate proximal neck length, or unfavorable angulation) is significant, estimated to be between 10-20% of all EVAR candidates
These challenging anatomies are more common in older patients, those with significant atherosclerotic burden, and individuals with connective tissue disorders
The decision to employ an iliac conduit is based on detailed pre-operative imaging and careful anatomical assessment.
Clinical Significance:
For DNB and NEET SS surgical candidates, understanding iliac conduit creation for EVAR access is crucial as it represents an advanced technique for managing complex vascular pathologies
It highlights the adaptability of surgical and endovascular strategies to overcome anatomical limitations, thereby expanding EVAR candidacy to a broader patient population
Mastering this concept is vital for managing challenging AAA cases, ensuring safe and effective repair, and preventing complications associated with inadequate graft sealing
It also underscores the importance of multidisciplinary approaches in modern vascular surgery.
Indications
Primary Indications:
Severe infrarenal neck angulation (>60 degrees)
Inadequate infrarenal neck length (<15 mm)
Significant iliac artery stenosis or occlusion precluding proximal graft sealing
Extensive iliac artery calcification or thrombus that compromises stent graft apposition
Unfavorable iliac artery anatomy (tortuosity, small diameter) making guidewire and stent graft delivery difficult
Prior infrarenal endarterectomy or aortoiliac reconstruction
Absence of a suitable proximal landing zone for standard EVAR due to anatomical distortion or disease.
Contraindications:
Unfavorable patient anatomy for accessing the conduit itself (e.g., extremely high BMI, extensive retroperitoneal fibrosis)
Significant comorbidities precluding major open surgical intervention and prolonged operative time
Active infection
Inability to achieve adequate proximal landing zone in the common iliac artery even with conduit
Absence of suitable distal landing zone in the external iliac or common femoral arteries.
Patient Selection:
Careful pre-operative assessment using multi-detector computed tomography angiography (MDCT) is paramount
Evaluation includes detailed measurement of the infrarenal neck length, diameter, angulation, and the extent and severity of iliac and common femoral artery disease
Aorta-iliac tortuosity, calcification patterns, and suitability of available venous or prosthetic material for conduit creation are assessed
The patient's overall physiological status and comorbidities are also considered.
Surgical Techniques
Conduit Materials:
Autologous saphenous vein (great saphenous vein) is preferred due to its thrombogenicity profile and biological compatibility
If autologous vein is unavailable or inadequate, synthetic grafts (e.g., PTFE, Dacron) can be used, often with an antibiotic coating
Reconstituted venous conduits or cryopreserved allografts are less commonly employed but may be options.
Surgical Approach:
Typically involves a low midline or left flank incision to access the infrarenal aorta and both iliac arteries
The common iliac artery is selected for proximal anastomosis, and the contralateral common iliac or external iliac artery is prepared for distal anastomosis
A healthy segment of the iliac artery is identified for end-to-end or end-to-side anastomosis of the conduit
The conduit is then tunneled through the retroperitoneum to the contralateral iliac artery or the distal aorta if a bifurcated graft is used.
Anastomotic Techniques:
Proximal anastomosis is usually performed end-to-end or end-to-side to a healthy segment of the common iliac artery
Distal anastomosis is typically end-to-end to the contralateral common or external iliac artery
Careful construction of tension-free, watertight anastomoses using appropriate sutures (e.g., 3-0 or 4-0 Prolene) is critical to prevent leaks and thrombosis
The length and diameter of the conduit are tailored to the specific patient anatomy and the EVAR device.
Hybrid Strategy:
The conduit serves as an extended proximal landing zone
After conduit creation and successful anastomosis, guidewires and the EVAR device are advanced through the conduit into the infrarenal aorta
The stent graft is then deployed with its proximal seal within the conduit, allowing for secure sealing and preventing endoleak
The distal extent of the EVAR graft typically lands in the common iliac or external iliac artery.
Preoperative Preparation And Imaging
Imaging Modalities:
Multi-detector computed tomography angiography (MDCT) is the gold standard for detailed anatomical assessment
It provides multiplanar reconstructions, 3D renderings, and diameter measurements crucial for planning
Magnetic resonance angiography (MRA) may be used in patients with contraindications to CT contrast
Ultrasound can provide supplemental information but is less comprehensive for complex anatomy.
Anatomical Measurements:
Key measurements include infrarenal neck length, diameter, and angulation
common iliac artery diameter, angulation, and length of healthy segment
external iliac artery diameter
and common femoral artery diameter
Assessment for thrombus burden, calcification severity and distribution, and tortuosity is essential
The distance from the renal arteries to the bifurcation and to the iliac arteries is also critical.
Risk Assessment:
A comprehensive assessment of cardiovascular, pulmonary, and renal function is performed
Frailty, sarcopenia, and overall anesthetic risk are evaluated
The potential for bleeding, infection, and prolonged operative time must be discussed with the patient and the surgical team
Multidisciplinary input from cardiology, anesthesiology, and radiology is often beneficial.
Postoperative Care And Monitoring
Immediate Postoperative Care:
Patients are typically managed in an intensive care unit (ICU) or a high-dependency unit
Close monitoring of hemodynamics (blood pressure, heart rate), urine output, and oxygen saturation is essential
Pain management is critical
Hemoglobin and hematocrit levels are monitored for evidence of bleeding
Early mobilization is encouraged to prevent deep vein thrombosis (DVT) and pulmonary complications.
Surveillance Protocol:
A structured surveillance protocol is vital
This includes early post-operative imaging (CT angiography at 1 month) to assess graft patency, exclude endoleaks, and evaluate the conduit anastomosis
Subsequent surveillance at 6 months, 1 year, and annually thereafter with duplex ultrasound or CT angiography is standard to monitor for late complications like endoleak, graft limb occlusion, or pseudoaneurysm formation at the anastomosis.
Antithrombotic Therapy:
Dual antiplatelet therapy (e.g., aspirin and clopidogrel) is typically initiated post-operatively, especially if synthetic conduit material is used, for a period of 1-6 months
Long-term aspirin therapy is often continued indefinitely to maintain patency and prevent thromboembolic complications
Anticoagulation may be considered in specific high-risk scenarios or for patients with underlying coagulopathies.
Complications
Early Complications:
Bleeding from anastomoses or surgical site
Graft infection
Conduit thrombosis or occlusion
Endoleak (Type I, III, or IV) due to inadequate seal within the conduit or distal to it
Myocardial infarction or stroke
Renal failure
Deep vein thrombosis (DVT) or pulmonary embolism (PE).
Late Complications:
Conduit pseudoaneurysm formation
Late graft limb occlusion or stenosis
Type III endoleak (modular component failure) or Type V endoleak (trans-graft degradation)
Rupture of the aneurysm sac or EVAR graft
Distal embolization
Infection of the conduit or EVAR graft.
Prevention Strategies:
Meticulous surgical technique with precise suture placement and avoidance of tension at anastomoses
Careful conduit selection and appropriate graft material
Pre-operative optimization of patient's comorbidities
Strict adherence to sterile surgical techniques
Aggressive post-operative antithrombotic therapy
Comprehensive surveillance protocol to detect and manage complications early
Use of stent grafts with proven track records and appropriate oversizing.
Key Points
Exam Focus:
Understand the indications for iliac conduit creation in complex EVAR
Differentiate between autologous vein and synthetic conduits
Recognize the critical role of pre-operative MDCT for anatomical assessment
Grasp the principles of conduit construction and anastomosis
Identify common early and late complications
Recall the post-operative surveillance strategy and antithrombotic regimen.
Clinical Pearls:
When planning an iliac conduit, ensure ample healthy proximal and distal landing zones are identified in the iliac arteries
For vein conduits, choose the longest, largest diameter segment of saphenous vein available and ensure it is adequately prepared
Tension-free anastomoses are paramount for graft survival
Consider tunneling the conduit laterally to avoid kinking and compression
Always have a contingency plan for bailout strategies if endovascular deployment fails.
Common Mistakes:
Inadequate pre-operative anatomical assessment leading to suboptimal conduit placement or graft choice
Poorly constructed or kinked anastomoses resulting in thrombosis or leak
Failure to achieve a secure seal within the conduit
Insufficient antithrombotic therapy or surveillance leading to late complications
Treating the conduit as an afterthought rather than an integral part of the EVAR plan.