Surgical Treatment of Sac Enlargement Due to Type II Endoleaks Following Endovascular Aneurysm Repair

Abstract

An aneurysm sac enlargement caused by type II endoleak (T2EL) following endovascular aneurysm repair (EVAR) for abdominal aortic aneurysms may cause serious complications such as rupture. Consequently, methods that preoperatively prevent or postoperatively treat T2EL have been employed. When significant aneurysm enlargement occurs due to persistent T2EL, embolization is first performed through several access points. However, although these endovascular reinterventions have a high technical success rate and are safe, their effectiveness remains questionable. When such endovascular procedures fail to stabilize sac enlargement, open surgical conversion (OSC) becomes the last-resort treatment option. We review several strategies of OSC for the repair of T2EL following EVAR. Among the three main OSC procedures, namely, complete endograft removal, partial endograft removal, and complete endograft preservation, partial endograft removal under infrarenal clamping was considered the most appropriate owing to its less invasiveness and durability.

Introduction

An aneurysm sac enlargement due to various endoleaks (ELs) following endovascular aneurysm repair (EVAR) for abdominal aortic aneurysm (AAA) may result in serious complications, including rupture. Several studies have shown the involvement of type II endoleaks (T2EL) in aneurysm enlargement and aneurysm-related deaths.^1–3) Consequently, methods that preoperatively prevent or postoperatively treat T2EL have been employed.

In cases wherein significant aneurysm enlargement has occurred due to postoperatively persistent T2EL, transarterial, percutaneous translumbar, or transabdominal embolization is performed through multiple access points to reduce the risk of rupture or penetration into the intestines. Most of these embolization procedures are safe, and their technical success rate is as high as 80%–90%.^4–7) However, their clinical success rate is not always satisfactory, wherein sac shrinkage or stabilization is only achieved in 50%–70% of patients, and multiple embolization procedures are required in some cases.^4–7) Continuous sac enlargement after endovascular T2EL treatment is observed in up to 30% of patients.^4,5)

Thus, when such endovascular procedures fail to stabilize sac enlargement, open surgical conversion (OSC) becomes the last-resort treatment option. This article discusses the surgical strategy for treating sac enlargement caused by T2EL.

Strategies of OSC

Complete endograft removal

The most radical OSC procedure involves complete endograft removal and aortic reconstruction using a transperitoneal or retroperitoneal approach. The main body of the endograft is implanted just below the renal artery, and suprarenal aortic cross-clamping is performed to completely remove the endograft. However, in the case of a suprarenal fixation stent, supramesenteric or, in most cases, supraceliac aortic cross-clamping is required.^8–10) Otherwise, an aortic occlusion balloon is inserted through the axillary artery and inflated at the top of the endograft. In cases of suprarenal cross-clamping, adequate renal protection using cold crystalloid perfusions can be routinely applied to limit the injury caused by prolonged renal ischemia.

Complete removal of an endograft with suprarenal fixation is difficult, whereas a technique that utilizes a 20-mL syringe cylinder is easy and time-saving. The supraceliac clamping period can be <2 min, and aortic clamping can be immediately shifted to the level of the infrarenal aorta.¹¹⁾

Distal cross-clamping of the iliac and femoral arteries is performed on both sides. The aneurysm sac is opened through a longitudinal arteriotomy, with identification and removal of the endograft.^8,9) Thereafter, a new bifurcated graft is routinely replaced in the aneurysm, paying special attention to the arterial degeneration of the proximal and distal parts and to Teflon felt reinforcement.

Partial endograft removal

Complete removal of an endograft is associated with high mortality and morbidity rates, especially when supravisceral clamping is recommended, and when the aneurysm enlargement is believed to be caused by T2EL without any evidence of endograft infection, partial endograft removal is considered.^12,13)

Proximal and distal cross-clamping is conducted on the infrarenal and iliac arteries under systematic heparin administration, the aneurysm sac is opened through a longitudinal arteriotomy, and the EL type is determined. When the T2EL is caused by the inferior mesenteric artery (IMA), lumbar arteries, or median sacral artery, all the bleeding side branches are oversewn from inside the sac, and the removal range is determined by confirming any deterioration or misalignment of the endograft. Furthermore, the temporary release of proximal or distal cross-clamping can confirm the presence of occult T1a or T1bEL.

To reduce the risk of late dilation of the residual aortic wall, both the aortic wall and endograft are carefully transected at the proximal neck, and a proximal anastomosis is formed with the standard prosthetic bifurcated graft in an end-to-end fashion. Anastomosis is performed with the stitches passing through the aortic wall and endograft.^14,15) A Teflon felt strip is used to reinforce the anastomosis, and in cases of proximal neck dilation, this collar around the proximal neck helps reduce the aortic radius.¹⁴⁾

Furthermore, the bifurcated graft is sewn distally at the iliac level according to the patients’ anatomic morphology. When the iliac endograft is well incorporated into the vessel wall, the distal portion of the endograft can be preserved, and the legs of a bifurcated graft can be anastomosed to the transected iliac endograft.^8,9,14,16)

OSC with complete endograft preservation (semi-conversion technique, endoaneurysmorrhaphy)

Complete endograft preservation for T2EL is less invasive as aortic clamp and graft replacement are not required. In cases where the aneurysm is opened and the absence of T1EL or T3EL is confirmed, this technique can also be used.

The aneurysm is exposed using the transperitoneal or retroperitoneal approach. Thereafter, all the branches, including the IMA, lumbar arteries, and median sacral artery, are ligated from the outside if possible and oversewn from the inside of the aneurysmal wall.^17–19) When occult T1EL is encountered, proximal neck banding should be performed.¹⁹⁾ As a result, the entire endograft is preserved without removal. When major lumbar artery bleeding is encountered, proximal clamping is required, and an intra-aortic occlusion balloon is inserted through the femoral artery and inflated in the supraceliac aorta above the suprarenal stent to provide temporary hemostasis.^17,18) Bleeding or oozing inside the aneurysm sac is carefully inspected.

The aneurysm sac is partly resected and tightly closed over the endograft to decrease sac diameter to protect it from the intestines. It has been reported that wrapping of the aneurysmal sac with an equine pericardium is useful to avoid sac re-enlargement.¹⁹⁾

Discussion

When significant aneurysm enlargement occurs due to persistent T2EL, embolization is first performed through several access points.^4–7) However, although these endovascular reinterventions have a high technical success rate and are safe, their effectiveness remains questionable. When such endovascular procedures fail to stabilize sac enlargement, OSC becomes the last-resort treatment option. We review the several strategies of OSC for the repair of T2EL following EVAR.

Generally, among EVAR patients, 2%–5% of patients reportedly underwent OSC.^20–22) Female sex, large aneurysm (>6 cm in diameter), complex anatomy, and nonelective EVARs were reported as factors that increase the risk of OSC.²¹⁾ In 2021, Wu et al. have conducted a retrospective review of 56 patients who underwent a total of 119 interventions, wherein the patients were treated for expanding aneurysm sacs with T2EL following EVAR, of which 90% (n=107) were technically successful, 59% required additional interventions for sac growth, 21% required reinforcement of the proximal and distal seal zones, and 18% underwent open repair for definitive treatment. They further concluded that patients with T2ELs should undergo thorough assessment of all alternative EL types to ensure comprehensive treatment and minimize the need for multiple interventions.²³⁾

The outcomes after nonelective primary open AAA repair are well established, with 30-day mortality rates of 1%–20% reported following urgent intact open aneurysm repair and 30%–50% reported following emergency/ruptured presentations. Meanwhile, urgent/emergency OSC following EVAR has a significantly higher risk of 30-day mortality than nonelective primary open AAA repair (37% versus 24%).^{4,20,24–26)} Other contemporary review articles have demonstrated high mortality and morbidity of OSC following EVAR.^21,27,28) Decisions around OSC should be carefully made, but the prognosis will be poor if a rupture occurs.

A previous study that compared elective OSC and primary open AAA repair demonstrated that postoperative morbidity and mortality were similar when controlling for patient factors and cross-clamping position.²⁹⁾ When limited to cases wherein T2EL alone led to a rupture, hemodynamics disruption may be minimal. However, because every case may be complicated with occult T1EL or T3EL, optimal timing for OSC is crucial in cases wherein the aneurysm enlargement persists following endovascular reinterventions.

Complete endograft removal

Instead of adopting a technique that uses a 20-mL syringe cylinder, Popplewell et al. have proposed a new technique for the complete removal of the endograft with a suprarenal fixation stent attached, employing a disposable proctoscope as a device to facilitate safe removal of the endograft with minimal damage to the aortic wall.³⁰⁾ However, it is uncertain whether this method will always be successful. Our experience with the present case indicated that even complete removal of the main body of the Excluder stent graft with only barbs was difficult. The removal was conducted by cutting the main body of the Excluder using scissors and wire cutters; however, surprisingly, the polytetrafluoroethylene graft remained firmly adherent to the inner wall of the aorta.

Because complete endograft removal under suprarenal or supraceliac clamping is highly invasive and associated with increased morbidity and mortality, there is no need to completely remove the endograft if there is no evidence of infection.^12,13)

Partial endograft removal

Compared with complete endograft removal, partial endograft removal under infrarenal clamping is less invasive. Furthermore, as it is difficult to complexly reject the possibility of small suture holes or T4EL with the entire endograft left, it is safer to remove as much of the exposed endograft as possible. Our experience has demonstrated that if the infrarenal proximal neck can be secured with an infrarenal clamp, then graft replacement can be conducted using a technique that is almost identical to that of primary open AAA repair²⁹⁾ (Figs. 1A–1F).

Fig. 1 (A) The patients underwent endovascular aneurysm repair using an Endurant stent graft. The aneurysm enlargement due to type II endoleak caused proximal neck enlargement, which resulted in T1aEL and open surgical conversion 2.5 years later. (B) Proximal and distal cross-clamping is performed on the infrarenal and iliac arteries, and the aneurysm sac is opened through a longitudinal arteriotomy. (C) The aortic wall and endograft are carefully transected at the proximal neck, and a proximal anastomosis is formed with the standard prosthetic bifurcated graft in an end-to-end fashion. (D) The image shows the parts of the removed stent graft. (E) The anastomosis is performed with the stitches passing through the aortic wall and endograft. A Teflon felt strip is used for reinforcement of the anastomosis. (F) The image depicts the postoperative three-dimensional computed tomography scan of the patient following partial stent graft removal.

In addition, in our case, we performed partial removal and partial graft replacement of various endografts following EVAR and thoracic endovascular aortic repair (TEVAR), during which end-to-end anastomosis with Dacron grafts was achieved using this method of cross-clamping of the endograft through the aorta. If the endograft stent is self-expandable, the stent is rarely expected to suffer from damage or failure due to the clamp. However, if the aortic wall of the endograft sealing zone is fragile due to chronic inflammation and degeneration, it must be determined whether it can serve as an acceptable anastomotic site and whether reinforcement with Teflon felt is required³¹⁾ (Fig. 1E).

Veraldi et al. have reported promising results with the new aortic carrefour technique, which preserves the original endograft iliac limbs in an iliac artery anastomosis during partial endograft removal.⁸⁾ Marone et al. have warned that when the stent graft was resected at the level of the fabric to reduce risk, the cut stent struts would eventually damage the new graft or suture line. In cases wherein the stent struts had to be cut, special attention was paid to avoid direct impingement of the leftover spikes against the new aortic graft.³²⁾

OSC with endograft preservation (semi-conversion technique, endoaneurysmorrhaphy)

Endoaneurysmorrhaphy that combines sacotomy, ligation of the back-bleeding vessels, and endograft preservation for T2EL can reduce operation time and result in a less-invasive OSC. Short-term outcomes have demonstrated shrinkage of the aneurysm sac with a stable diameter, no missed T2EL, no T2EL recurrence, and no observations of endograft migration or disjunction.^17,18) In addition, in cases of endograft preservation, the proximal neck banding method may be able to prevent aneurysm re-enlargement and neck enlargement-induced T1aEL.^19,33)

Laparoscopic approaches without laparotomy may be effective only if the feeding arteries are ligated. A systematic review of laparoscopic ligation of the feeding arteries that cause T2EL demonstrated that it may be used as a potential alternative treatment method if standard endovascular embolization fails.^34,35) However, laparoscopic repair is technically challenging, even for experienced surgeons, due to frequent dense periaortic inflammation following EVAR.

However, these methods of OSC with endograft preservation approaches may overlook the proximal lumbar arteries in the neck, median sacral artery, or graft hole. It is recommended that the median sacral artery be ligated from the outside because its orifice is located between the bilateral iliac limbs. Furthermore, we have experience with a patient who underwent EVAR with an Endurant stent graft after being diagnosed with T2EL-induced aneurysm enlargement, which ruptured later. In this case, when the aneurysm was opened, a graft hole was observed on the ventral side of the main body, wherein the proximal end of the contralateral leg was in contact, and this T3bEL was the cause of the rupture. McWilliams et al. have reported a similar T3bEL case,³⁶⁾ and a previous review of 23 articles indicated that the leak locations are often at the main body or flow divider; however, T3bEL is believed to occur regardless of the device used,³⁷⁾ given that the endograft preservation method may not be able to identify small graft holes.

Furthermore, Torikai and Takahashi et al. have published a case report of continuous aortic aneurysmal growth following EVAR caused by atypical T2EL without EL cavities through developed vasa vasorum, which are known as the vessels associated with arterial microcirculation.^38,39) Thus, it is better to remove the aneurysmal wall to the extent possible in endoaneurysmorrhaphy.

An Italian multicenter registry study compared the results of a complete or partial endograft explantation group and an endograft preservation group. It reported that the endograft preservation group had lesser postoperative complications. However, the increased rate of persistent and/or recurrent EL reduced the durability of medium-term results.⁴⁰⁾

Until further studies on long-term outcomes are collected, the endograft preservation method may only be advised in cases wherein partial removal is difficult.

Type 5 EL and timing of OSC

Surgical treatment of T2EL after endovascular aortic repair has thus far been described. However, it is often difficult to determine all EL classifications preoperatively. A meta-analysis of OSC in 28 studies (1,093 patients) revealed that 44.4% of the indications were ELs, with T1EL being the most common at 22.8%, followed by T2EL at 15% and T3EL at 8.9%. The number of cases of OSC due to T2EL is not small, but the fact that T5EL accounted for 7.2% is also noteworthy.¹²⁾ The problem is the existence of T5EL or endotension causing aneurysm enlargement, although there is no contrast effect at all in the aneurysm.^41,42)

Of the 420 patients who underwent EVAR between 2006 and 2022 at our hospital, 7 underwent OSC, and 4 (1.0%) underwent OSC with aneurysm enlargement due to T2EL. Of these patients, two first underwent catheter-based arterial embolization via the lumbar artery; however, OSC was then performed due to persistent aneurysm enlargement. In another patient, aneurysm enlargement due to T2EL caused proximal neck enlargement, which resulted in T1aEL and OSC (Fig. 1). Because the final patient did not exhibit any nidus in the aneurysm due to T2EL, primary OSC was conducted, but none of the ELs were observed even when the aneurysm sac was opened, and the thrombi were all removed. We performed graft replacement with partial endograft removal instead of endograft preservation because all four patients tolerated open repair, and there was a concern that the aneurysm would enlarge once again after OSC due to T5EL, overlooked T3bEL, or T1EL, which would render a second open repair challenging.

Of the 420 cases in our hospital, 15 (3.6%) exhibited aneurysm enlargement due to T5EL, but because no contrast findings were observed in the aneurysm, endovascular treatment was difficult to apply, and we hesitated to conduct a primary OSC given the background of the patient. In addition, we experienced a similar case after TEVAR, which left us concerned about whether T1EL would eventually occur as a result of losing the proximal and distal landing zones during each outpatient examination. There is still debate about what should be done in the endovascular approach for T5EL as well as when OSC intervention should be performed.

Eden et al. have reported that in a study conducted on 389 patients with an average follow-up of 58.8 months (range, 0–194 months), the follow-up imaging diagnosed 124 patients with T2EL (32%). The average sac size increase at which T1aEL developed in patients with T2EL was further found to be 13 mm.⁴³⁾

The absolute value of the aneurysm diameter and the extent of rapid expansion, both of which are factors for OSC, may vary across cases and patients, indicating the need to identify some general indicators.

Conclusion

We investigated three main methods of open surgical treatment for sac enlargement caused by T2ELs after EVAR. Among them, the most radical was a complete endograft removal with aortic reconstruction. However, complete endograft removal under supravisceral clamping is highly invasive and has been associated with increased morbidity and mortality rates. On the other hand, complete endograft preservation is less invasive as aortic clamps and graft replacements are not required. In these cases, the aneurysm is opened, and all the side branches are oversewn from the inside of the aneurysmal wall. The aneurysm sac is then partially resected and tightly closed over the endograft. However, the long-term results of the complete endograft preservation method may be problematic, especially considering T3bEL, atypical T2EL, and T5EL. Partial endograft removal under infrarenal clamping is less invasive than complete endograft removal and is considered safer and more durable than complete endograft preservation.

It is expected that the number of patients for whom EVAR would be recommended will increase in the future with continuous improvement in devices. As the prognoses of those patients are prolonged, there may be an increase in the number of cases with aneurysm sac enlargement due to T2ELs or other ELs as well as the number of OSC interventions. Strict follow-up and adequate OSC techniques must be adopted to reduce long-term aneurysm-related mortality following EVAR.

Conflict of Interest Statement

The authors declare no conflicts of interest in association with the present study.

Author Contributions

Study conception: SO

Data collection: SO

Analysis: SO

Investigation: all authors

Manuscript preparation: all authors

Funding acquisition: -

Critical review and revision: all authors

Final approval of the article: all authors

Accountability for all aspects of the work: all authors