Unfavorable anatomy for abdominal aortic aneurysm (EVAR)
Anatomic factors can be a major limitation for stent-graft placement. The main problem often lies in the morphology of the aneurysm neck—the healthy segment of the aorta located just below the renal artery ostia.
Main technical obstacles:
- Short neck: critically short distance for fixation. The neck may also have an unfavorable shape (e.g., short conical or barrel-shaped).
- Pronounced angulation: the angulation between the suprarenal segment and the neck can reach 90 degrees. The neck lies almost horizontally, preventing adequate positioning.
- Wall lesions: presence of severe atheroma, mural thrombus, or focal ulceration (especially on the posterior wall) in the intended fixation zone.
- Narrow access: advancing a large-caliber delivery system through stenotic or tortuous iliac arteries risks rupture. In such cases, a conduit or the Pave and Crack technique is used (placement of a preliminary graft with intentional rupture of the native vessel wall from the inside).
Features of thoracic aortic interventions (TEVAR)
In the endovascular treatment of thoracic aortic aneurysms (Thoracic Aortic Aneurysm, TAA), the geometry of the aortic arch and the localization of the pathology according to the Stanford classification play a key role (type B is suitable for TEVAR, type A is generally not).
Arch angulation presents a particular challenge:
- Norman arch (Norman arch): the arch has a smooth, curved shape. This is a favorable variant for endovascular repair.
- Gothic arch (Gothic arch): the arch has a pointed apex with a sharp angle. With this anatomy, the stent-graft apposes poorly to the wall along the lesser curvature. This results in the «beaking» effect (beaking): blood flows around the graft rather than through it, which can cause the device to fold inward and leads to a dangerous type 1 endoleak (type 1 endoleak).
If the length of healthy aorta is insufficient for sealing, the stent may cover the left subclavian artery ostium. To prevent ischemia, the fixation zone is extended using preliminary debranching (e.g., carotid-subclavian bypass surgery).
Deployment mechanics and postoperative complications
Stent-grafts expand due to the intrinsic radial force of the annular stent as the sheath is retracted. During deployment in the thoracic segment, high-velocity blood flow can displace the device—this is the so-called «windsock effect» (windsock effect). Rapid pacing is used to temporarily lower blood pressure for precise positioning.
Despite a 30-day survival rate of 96%, the procedure carries certain risks:
- Spinal cord ischemia: occurs when the artery of Adamkiewicz (usually at T8–L1 level) or intercostal arteries are covered. Unlike open surgery, these vessels cannot be re-implanted endovascularly. As a prophylaxis in high-risk cases, a lumbar cerebrospinal fluid drain is used.
- Stent-graft kink: severe deformation (severe kink) causes luminal stenosis within the prosthesis itself. Treatment tactics include balloon dilation and reinforcement of the kinked zone with an additional bare-metal stent (bare stent).
- Access vessel injury: rupture of the external iliac artery, visualized on CT as contrast extravasation. It is managed by implanting a covered stent at the rupture site.
Briefly: answers to topical questions
What types of endoleaks exist after endovascular aortic repair?
Following endovascular aortic repair, 5 types of endoleaks are distinguished. Sources describe the following in detail:
- Type 1 (Type 1 endoleak) — occurs due to inadequate seal between the device and the aortic wall. Subdivided into type 1A (proximal end), type 1B (distal end), and type 1C (lack of seal at the occluder site).
- Type 2 (Type 2 endoleak) — occurs due to retrograde blood flow into the aneurysmal sac from small branch vessels (intercostal, lumbar, or inferior mesenteric arteries).
- Type 3 (Type 3 endoleak) — occurs due to a defect in the fabric (material) of the prosthesis itself.
What are the absolute contraindications to endovascular repair of an abdominal aortic aneurysm?
Absolute contraindications for endovascular treatment of aortic pathologies include the following conditions:
- Lack of patient consent (Lack of patient consent).
- Limited life expectancy — in cases where the risks of intervention outweigh the potential benefit.
- Low cardiopulmonary reserve or other comorbid conditions — if the risks of intervention outweigh the benefits.
- Unstable patients — if the clinical condition does not allow tolerating the short delay required for imaging the pathology.
- Ascending aortic pathology — except in situations where there is absolutely no surgical alternative.
What are the indications for TEVAR in descending thoracic aortic aneurysm?
Endovascular repair (TEVAR) is indicated when the risk of aneurysm rupture outweighs the risk of the surgery itself. The indications include:
- Asymptomatic descending aortic aneurysm — when reaching a diameter of 5.5 cm (or 4.3 cm in Marfan syndrome).
- Rapidly growing aneurysms — with a growth rate of ≥1 cm/year, treatment is required regardless of size.
- Symptomatic aneurysms — treated regardless of size.
- Pseudoaneurysms, saccular, and mycotic aneurysms — require early intervention due to a higher risk of rupture compared to fusiform degenerative aneurysms.
What complications can occur in the early postoperative period after EVAR?
Sources describe the following complications after EVAR:
- Endoleaks (endoleaks) — presence of blood flow in the aneurysm sac outside the stent-graft.
- Endograft complications — migration, component separation, kinking (kinking), or limb occlusion.
- Graft infection (graft infection) — may be accompanied by gas within the aneurysm sac after the early postoperative period and inflammatory stranding of the periaortic fat.
- Aortoenteric fistulas (aortoenteric fistulas) — a rare, severe complication that can be the cause or consequence of graft infection.
- Vascular access complications — specifically, vessel rupture or avulsion during the passage of the delivery system.
To evaluate aortic arch geometry in TEVAR, recall architecture: the Norman style (Romanesque) features broad, smooth arches (favorable). The Gothic style features pointed arches (high risk of type 1 endoleak and the beaking effect).
Class and exam questions
Is aneurysm rupture an absolute contraindication for EVAR?
No, neither aneurysm rupture, nor the presence of malignancy or mycotic etiology of the aneurysm are contraindications for endovascular intervention.
How is the problem of narrow access vessels managed if the delivery system is too large?
Angioplasty, placement of a temporary surgical conduit above the stenosis, or the Pave and Crack technique (rupturing the native artery from the inside after placing a reinforcing stent) are used.
What is the core concept of PEVAR?
PEVAR (Total Percutaneous Endovascular Aneurysm Repair) is a fully percutaneous repair using low-profile systems and suture-mediated closure devices. It avoids an open incision, reducing pain and hospital stay.
What else to study on this topic
- Acute aortic syndrome (dissection, intramural hematoma, penetrating ulcer)
- Types of endoleaks and methods for their endovascular management
- Anatomy of spinal cord blood supply in the context of aortic surgery
- Stanford classification of aortic dissections
- Absolute and relative contraindications to aortic surgery
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