Abstract
Despite the broad implication of endovascular aneurysm repair (EVAR), robust evidence concerning the treatment of type II endoleaks is missing. Ethylene-Vinyl-Alcohol-Copolymer Liquid Embolic Agent (Onyx) is a therapeutic modality for type II endoleaks following EVAR when the aneurysm sac has grown with more than 5mm in 6 months.
Cannulation of the nidus and use of onyx allows controlled delivery minimizing the risk of inadvertent embolization of a non-target location treating the inflow but also outflow of the endoleak simultaneously. Potential disadvantages of this technique include the transient halitosis, unpleasant body odor postoperatively, high costs, and risk of vasospasm of vessels correlated with bowel perfusion.
Keywords
aneurysm repair, embolization, endoleak type II, fluid agents, onyx
Treatment of abdominal aortic aneurysms (AAAs) has evolved significantly during the last two decades, especially with the broader introduction of endovascular aneurysm repair (EVAR) by Parodi et al. in 1991. However, the Achilles’ heel of EVAR remains the endoleak.
Many early type II endoleaks are transient and will resolve spontaneously within 6 months with conservative treatment alone. When a type II endoleak is associated with aneurysm sac enlargement of more than 5 mm, however, treatment of the endoleak is necessary. Different treatment options have been described, including embolization through a transarterial, lumbar (direct puncture), and caval route; laparoscopic ligation; and open surgical repair. Onyx is an embolic agent approved by the U.S. Food and Drug Administration (FDA) for the embolization of arteriovenous malformations in the brain. A similar predecessor compound was first described in the early 1990s by Taki et al. and Terada et al. .
Onyx is an ethylene-vinyl-alcohol copolymer (EVOH) dissolved in dimethyl sulfoxide (DMSO) and suspended micronized tantalum powder (Medtronic, Santa Rosa, California, USA). There are three possible concentrations:
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Onyx LES (liquid embolic system) 18 (6% EVOH)
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Onyx LES 34 (8% EVOH)
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Onyx HD 500 (20% EVOH)
The greater the amount of copolymer, the higher the viscosity. Solidification takes place within 5 minutes after injection.
Preoperative Evaluation
Multislice (1.0-mm) computed tomography angiography (CTA) with arterial and venous phases is performed to define the endoleak anatomically. Inflow from two main sources is responsible for the development and persistence of type II endoleaks:
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Flow into the aneurysm sac from the inferior mesenteric artery (IMA) via the Riolan anastomosis and the superior mesenteric artery (SMA)
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Lumbar or middle sacral artery inflow originating from the hypogastric artery and via the iliolumbar artery to the feeding branch vessels
Combined inflow from both the IMA and the lumbar vessels can also occur.
Once the location of the vessels feeding and draining a type II endoleak is confirmed, transarterial embolization with Onyx is our preferred approach in Münster, Germany. Fig. 19.1 shows CTA of a patient with type II endoleak originating from the IMA.
When no inflow vessels are detected, or a transarterial attempt fails, a translumbar approach becomes the therapy of choice. Ultimately, if endovascular treatment of a type II endoleak fails, continued aneurysm enlargement dictates a more invasive therapy, such as open surgical repair ( Fig. 19.2 ).
Surgical Approach
Onyx embolization can be performed through brachial or common femoral artery access. We prefer the transbrachial approach, to avoid a 180-degree orientation of the sheath and catheter in relationship to the iliolumbar artery through the ipsilateral internal iliac artery with transfemoral access. If the patient is very tall, a transaxillary approach is mandatory to have enough catheter length to reach the iliolumbar artery. We perform the procedure usually with the patient under general anesthesia.
Procedure
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The left brachial artery is punctured and a short, 4-French (4F) sheath introduced using Seldinger technique.
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Heparin (5000 IU) is administered.
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A 0.035-inch, soft Terumo wire is advanced into the ascending aorta. After rotation of the pigtail catheter and on rapid advancement of the wire, the catheter can be easily advanced into the renovisceral aortic segment.
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Over a stiff wire, a 6F Shuttle sheath of 90 cm (Cook, Bloomington, Indiana, USA) is placed in the renovisceral aortic portion.
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With a soft wire and a vertebral catheter, the SMA is cannulated ( Fig. 19.3 ). After identification of the Riolan anastomosis ( Fig. 19.4 ), both the sheath and the vertebral catheter are advanced as far as possible.
