Thoracic Endograft for Abdominal Aortic Aneurysms,an Unusual Application for Severe Neck Angulation: Case Report and Literature Review

Case History

An 82-year-old male patient was admitted following 2 days of acute thoracic-abdominal pain. An urgent thoracic-abdominal multiple–slice, 5 mm, contrast-enhanced computed tomographic (CT) scan revealed a 9.8 cm diameter abdominal aortic aneurysm (AAA), with a calcified and angulated neck but without signs of acute rupture or dissection (Figure 1). An acute coronary syndrome in evolution was identified, and the patient was submitted to an urgent coronarography with percutaneous transluminal coronary angioplasty and stenting.

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Figure 1.

Preoperative computed tomography: possible indicators of a symptomatic or recent contained aneurysm rupture. A, Irregularity of the right parietal wall. B, Suspected left posterior contained rupture.

Evaluation of the CT scan showed an aortic neck with a diameter of 22 mm and a length of 14 mm, an 80° suprarenal/infrarenal aortic neck angle, and a 90° infrarenal neck/aneurysmal longitudinal axis angle (Figure 2). Immediately following clinical cardiologic improvement, the patient was treated with EVAR for AAA under local anesthesia in a dedicated operating room with the use of a portable C-arm (OEC 9800, GE Medical System, Salt Lake City, UT) by a skilled endovascular team.

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Figure 2.

Preoperative computed tomography: severe angulation of both the supra- and infrarenal aortic neck.

Proximal sealing was performed first, with a straight 24 × 90 mm Relay thoracic endograft (Bolton Medical, FL) placed just below the distal renal artery, confirmed with intraoperative angiography. A Powerlink bifurcated endograft 28 × 16 × 120 mm (Endologix Inc, Irvine, CA) was then delivered inside the Relay endograft, placed distally on the aortic bifurcation, with an overlapping zone of 53 mm. Postdilation of the overlapping zone was performed with a Coda 30 mm balloon (Cook Inc., Bloomington, IN).

A CT angiogram confirmed ongoing aneurysm exclusion with correct graft positioning and aneurysm sac reduction of 8 mm 6 months postoperatively (Figure 3).

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Figure 3.

Postoperative computed tomography at 6 months: continued aneurysm sac exclusion without migration of either graft.

Discussion

Patient selection based on anatomic characteristics is essential. ^1,3,8 However, increasing EVAR experience has led to a widening of patient selection. ^3,6,7,9

The presence of severe neck angulation (SNA) (an angle > 60° between the infrarenal aortic neck and the aneurysm's longitudinal axis) is a frequent anatomic characteristic, present in 22.2% of the EUROSTAR database patients. ² Initial studies found no correlation between SNA and EVAR outcomes. “Hostile” necks ⁴ were not found to be associated with type I proximal endoleak, ^7,8 migration, or other adverse outcomes. ^3,10 These studies, however, are limited by small population sizes, short-term follow-up, and unclear definitions of SNA.

Conversely, recent articles have demonstrated poor outcomes associated with SNA. Albertini and colleagues identified neck angulation as the most important factor determining proximal type I endoleak and migration. ¹¹ The hypothesis that stent graft stiffness was a cause of proximal seal failure was confirmed. As reported by the authors, blood flow through an endograft acts as a displacing force. In SNA, the endograft is curved, resulting in a larger force exerted on the outer wall; thus, the displacement force is exaggerated. The adhesion of the graft to the neck's wall may be irregular and weakened in SNA, leading to a smaller contact surface and thus lower friction forces.

Sternberg and colleagues found that SNA influenced both early and late outcomes, particularly in patients with moderate (40–59°) and severe (> 60°) neck angulation. ⁵

A review of 1,152 EUROSTAR patients with SNA found a statistically significant higher rate of type I proximal endoleak, 30-day migration, and secondary procedures. ² Results analysis by various single devices showed no significant differences.

Despite adverse morphology, EVAR was considered attributable to the patient being unfit for surgery. Possible device assessment included both the Excluder and the Zenith AAA endografts. The Excluder endograft was assessed as being highly adaptable in tortuous anatomy, but given the SNA of 90°, we questioned sufficient parietal adherance, assigning this choice a high risk of migration. The Zenith endograft permits an active suprarenal fixation and a long main body, but the proximal, somewhat rigid structure seems less adaptable in anatomy with both a tortuous suprarenal and an infrarenal neck, risking proximal endoleak. Sternberg and colleagues stated that the angle between the suprarenal aorta and the infrarenal aortic neck was more frequently noted in patients who also had severe angulation between the infrarenal aortic neck and the aneurysm-an important influence on the success of EVAR with suprarenally fixed endografts. ⁵ Furthermore, the hooks of the Zenith endograft could have been exposed at the level of the renal arteries, causing possible arterial damage. Given the extreme tortuosity, it would have been difficult to cannulate the stump with both modular devices. Although fenestrated stent grafts are specifically designed to overcome short anatomic neck lengths, this treatment is still considered experimental, time consuming (there is usually a 3-week delay for custom-made devices), and costly.

Thoracic stent grafting technological advancements have recently focused on stent graft adaptation to the natural curve of the thoracic aortic arch and the delivery system in complex and especially tortuous anatomies, rendering them more adaptable in SNA compared with currently available abdominal endografts. The Relay endograft is preangulated with a varying radial force and good full-body apposition. ¹² The proximal fixation of thoracic stent graft study by Canaud and colleagues concluded that hooks do not improve fixation and that secure proximal anchorage is mainly influenced by radial force and a proximal open stent segment. ¹² The authors believe that the Valiant endograft could also have been an appropriate choice. An article on infrarenal AAA treated with a thoracic endograft has already been published for the successful treatment of an extremely large infrarenal neck (40 mm). ¹³

The Powerlink bifurcated endograft was deployed on the aortic bifurcation for complete sealing of the aneurysm. The Powerlink endograft was chosen owing to its positioning on the aortic bifurcation, in turn offering additional stability to the thoracic endograft by reducing the chance of migration and kinking. ^14,15 Further, its long body also offered increased stability with an ample overlap, without the presence of hooks and barbs. Postprocedural dilatation of the overlapping zone was designed to reduce the risk of type III endoleak. The use of multimanufacturer hybrid devices is controversial; however, Cinè and colleagues concluded in a recent study of pull-out forces for modular stent graft systems that hybrid and nonhybrid forms exhibited similar pull-out forces when appropriate oversizing was used. ¹⁶

However, as we were unsure of obtaining adequate proximal sealing, the thoracic stent graft was deployed prior to the bifurcated graft. Ideally, the thoracic stent graft should be delivered after the bifurcated graft, reducing possible inadequate sealing at the overlapping zone. In the future, the unibody bifurcated graft could work as a base for EVAR with hybrid modular endografts.

Conclusion

Severe infrarenal aortic neck angulation is often associated with poor outcomes. In high-risk patients unfit for traditional surgical treatment, the adaptability of thoracic endografts could achieve adequate proximal sealing in strong neck angulation, permitting EVAR in otherwise unsuitable patients.