Internal iliac coverage during endovascular repair of abdominal aortic aneurysms is a safe option: A preliminary study

Abstract

Endovascular aneurysm repairs lacking suitable common iliac artery landing zones occasionally require graft limb extension into the external iliac artery, covering the internal iliac artery origin. The purpose of this study was to assess incidence of type II endoleak following simple coverage of internal iliac artery without embolization during endovascular aneurysm repair. Three hundred eighty-nine endovascular aneurysm repairs performed by a single surgeon (2004–2015) were reviewed. Twenty-seven patients underwent simple internal iliac artery coverage. Type II endoleak was assessed from operative reports and follow-up computed tomography imaging. No patient suffered type II endoleak from a covered internal iliac artery in post-operative computed tomography scans. Follow-up ranged from 0.5 to 9 years. No severe pelvic ischemic complications were observed. In conclusion, for selected cases internal iliac artery coverage without embolization is a safe alternative to embolization in endovascular aneurysm repairs, where the graft must be extended into the external iliac artery.

Keywords

Internal iliac artery endovascular aneurysm repair internal iliac artery coverage safety endoleak claudication

Introduction

Safety and efficacy of endovascular aneurysm repair (EVAR) has been conclusively demonstrated. Benefits over open surgery include lower perioperative morbidity and mortality, and long-term safety.^1–4 With growing operator experience and improved devices, increasingly complex and challenging anatomy is being considered for endovascular repair.

Appropriate landing zones both for the proximal and distal parts of the stent graft are mandatory for appropriate sealing of the aneurysm to prevent type I endoleaks. In the majority of cases, the common iliac artery (CIA) is the ideal landing zone, preserving flow to both the internal iliac artery (IIA) and external iliac artery (EIA).⁴

Certain cases, such as aortoiliac aneurysms, lack a suitable CIA landing zone. Here, the iliac limb of the stent graft must be extended into the EIA, thus covering the IIA origin (Figure 1). Previous investigations have reported the possibility of symptoms such as buttock claudication, pelvic ischemia, colonic ischemia, and sexual dysfunction as a consequence of the loss of antegrade blood flow into the IIA.^5–9

Figure 1.

Contrast-enhanced CT illustrating right IIA coverage by stent graft.

The mainstay of treatment in the aortoiliac aneurysm cases where the stent graft must be landed in the EIA is the prior sacrifice of the IIA by embolization.¹⁰ The rationale for this approach is that embolization, either using coils or plugs, prevents retrograde perfusion of the IIA origin, thus preventing subsequent type II endoleak and post-repair aneurysm dilation and rupture. However, this approach is potentially complex and cannot be employed in patients with tortuous iliac artery anatomy. Furthermore, this technique results in embolization of distal IIA branches leading to worse clinical ischemic outcomes.^6,8,9 Another option is iliac branch grafts, which increases complexity and cost; long-term outcomes are not well studied.^11–13

There is growing evidence that IIA coverage, without prior embolization may be a superior alternative that is technically simpler and more cost effective with low risk of type II endoleak and better clinical outcomes.^9,14,15 Reports exist demonstrating spontaneous thrombosis of the proximal IIA after coverage by stent graft, which has the additional benefit of preserving more collateral flow compared to embolization.

The present study aimed to determine the safety of IIA coverage during EVAR. The following were assessed: (1) presence of type II endoleak from the IIA post-coverage; (2) IIA branch patency to assess preservation of collateral pelvic circulation; (3) severe pelvic ischemia perioperatively and in clinical follow-up; (4) procedure-related complications.

Methods

Three hundred and eighty-nine consecutive EVARs performed by a single surgeon, at The Ottawa Hospital between October 2004 and February 2015, were retrospectively reviewed. Ethics approval was obtained from the Ottawa Hospital Research Institute prior to the commencement of the study.

Operative reports for all cases were reviewed to determine if the patient met study inclusion criteria. Inclusion criteria were aortic, aortoiliac, or CIA aneurysms that were treated via endovascular approach with IIA coverage, without prior embolization. Ruptured aneurysms were included in the cohort. Patients who underwent previous coil embolization of IIA prior to coverage by stent graft, as well as those with pre-existing ipsilateral IIA origin occlusion were excluded from the study.

Twenty-seven patients underwent repair fulfilling our inclusion criteria, wherein the IIA was covered but not embolized. The case notes were obtained for all identified cases including those pertaining to hospital inpatient admission, multidisciplinary team meetings, surgical consultation, clinical outpatient follow-up, and surgical operative record. Furthermore, all imaging for these cases was reviewed including pre- and post-operative imaging as well as radiological reports.

Data were collected on patient demographics, date of procedure, date of discharge, operative plan and procedural details, perioperative aneurysm morphology, operation-related complications, clinical findings, presence of type II endoleak, and IIA branch patency in CT imaging follow-up.

Imaging protocol

The routine imaging protocol for endovascular aneurysm repair at The Ottawa Hospital includes preoperative arterial contrast enhanced CT scan within six weeks of surgery; axial images are acquired from the diaphragm to the pubic symphysis. Post-operative contrast-enhanced CT examination is performed at one month, six months, one year and annually thereafter unless otherwise required by clinical or radiological findings.

Pre-operative planning and selection for IIA coverage

Aneurysms were monitored by ultrasound considering size and rate of growth over time. When they reached a size appropriate for repair (>5.5 cm for aortic aneurysms), CT angiography was performed. The IIA was covered in the following cases: (1) abdominal aortic aneurysms (AAA) with aneurysmal CIA; (2) CIA aneurysm only; (3) extension to prevent type Ib endoleak; (4) short CIA <2 cm; (5) diseased CIA; (6) mal-deployment.

Endovascular procedure

Endovascular stent placement was performed in an operating room with a portable C-arm X-ray image intensifier. Stents used for aortic repair included; Talent (Metronic), Endurant (Medtronic), Zenith (Cook), Anaconda (Terumo).

Study endpoints

The primary study outcome measures were frequency of type II endoleak from the covered IIA. Secondary endpoints included: IIA thrombosis and branch patency on CT follow-up, frequency of pelvic ischemic complications perioperatively and in clinical follow-up, and other procedure-related complications, namely: graft infection, migration, thrombosis, kinking, endoleaks, and patient death.

Statistical analysis

IBM SPSS Statistics Version 20 for Mac (IBM Corp., Armonk, New York) was used for statistical analysis. Normally distributed continuous variables are presented as means with standard deviations. Categorical variables are presented as frequencies and percentages.

Results

Of all EVARs retrospectively reviewed, 27 cases performed at The Ottawa Hospital between October 2004 and February 2015 met the inclusion criteria wherein the previously patent IIA was covered during endovascular repair without prior embolization. The study population comprised 27 (100%) men, mean age 76.5 ± 9.4 at time of operation. Patient demographics and baseline comorbidities are reported in Table 1.

Table 1.

Patient demographics and baseline characteristics.

Age at operation (years)	76.5 ± 9.4
Male	27 (100%)
Risk factors
Hypertension	22 (81.5%)
Diabetes mellitus	8 (29.6%)
Ischemic heart disease	15 (55.6%)
Chronic obstructive pulmonary disease	4 (14.8%)
Chronic renal failure	10 (37.0%)
Dyslipidemia	19 (70.4%)
Smoking history	7 (25.9%)
Current smoker	17 (63.0%)

Indications for IIA coverage were: AAA with aneurysmal CIA (16 cases, 59.2%), CIA aneurysm only (two cases, 7.4%), AAA with short CIA < 2 cm (three cases, 11.1%), AAA with graft extension into EIA to treat type Ib endoleak (four cases, 14.8%), severely diseased CIA preventing distal seal (one case, 3.7%), and mal-deployment (one case, 3.7%).

Baseline aneurysm morphology and operative outcomes

Pre-operative AAA size was 58.9 ± 13.5, and CIA diameter was 28.5 ± 10.8. IIA coverage was successful in 100% of cases (Figure 2). The following stent grafts were implanted: Talent and Endurant (Medtronic) (n = 24, 88.9%), Zenith (Cook) (n = 1, 3.7%), Anaconda (Terumo) (n = 2, 7.4%). The majority of cases were performed using bifurcated devices (n = 22, 81.5%), and the remainder with aortouniiliac stent grafts (n = 5, 18.5%). Intra-operative endoleak on completion angiogram was observed in 11 cases (40.7%); type I (n = 2), type II lumbar artery (n = 4, 14.8%), type II inferior mesenteric artery (n = 3, 11.1%), type IV (n = 2, 7.4%). Covered IIA was visualized on completion angiogram in eight (29.6%) patients. However, endoleak from covered IIA was not observed on completion angiogram for any of the cases. Mean length of hospital stay was 3.9 ± 3.8 days. Operative outcomes and baseline aneurysm morphology are summarized in Table 2.

Figure 2.

Digital subtraction angiographic image of left IIA coverage during EVAR.

Table 2.

Operative variables and baseline aneurysm morphology.

Graft company
Talent, Endurant (Medtronic)	24 (88.9%)
Zenith (Cook)	1 (3.7%)
Anaconda (Terumo)	2 (7.4%)
Graft configuration
Bifurcated	22 (81.5%)
Uni-iliac	5 (18.5%)
Reintervention	3 (11.1%)
Rupture	3 (11.1%)
Indication for coverage
AAA only	0 (0%)
AAA with aneurysmal CIA	16 (59.2%)
CIA aneurysm only	2 (7.4%)
AAA with short CIA (<2 cm)	3 (11.1%)
AAA; graft extended to exclude type Ib endoleak	4 (14.8%)
Other (severely diseased CIA, mal-deployment)	2 (7.4%)
Laterality – left	11 (40.7%)
Laterality – right	16 (59.3%)

Aneurysm morphology (Pre-op CT)
AAA diameter (mm)	58.9 ± 13.5
CIA diameters
Size at aortic bifurcation (mm)	22.8 ± 11.0
Maximum size (mm)	28.5 ± 10.8
Size at iliac bifurcation (mm)	19.7 ± 8.0
EIA diameter (mm)	9.3 ± 1.9
IIA diameter (mm)	10.4 ± 5.1
Intraoperative endoleak
Type I	2 (7.4%)
Type II
Lumbar	4 (14.8%)
Inferior mesenteric	3 (11.1%)
IIA	0 (0.0%)
Type IV	2 (7.4%)
Covered IIA visualized on completion angiogram	8 (29.6%)
Length of hospital stay (days)	3.9 ± 3.8

AAA: abdominal aortic aneurysms; CIA: common iliac artery; EIA: external iliac artery; IIA: internal iliac artery.

Post-operative follow-up and complications

Findings from contrast-enhanced CT scans performed (1) initially after EVAR, and (2) most recently, are reported. First CT scan was performed 25.3 ± 20.7 days post-operatively. Endoleak was observed in 11 cases (40.7%); type Ia (n = 3, (11.1%), type II lumbar artery (n = 3, 11.1%), type II median sacral artery (n = 1, 3.7%), type II inferior mesenteric artery (n = 3, 11.1%), type III (n = 1, 3.7%). Again, no endoleak from a covered IIA was observed in any patient. IIA thrombosis was observed in 85.2% of patients (n = 23), 92.0% of patients who could be assessed. In 19 patients (82.6%), this thrombosis occurred proximal to the first branch of the IIA Thrombosis was not observed in two patients (8.0%). Two patients could not be assessed due to patient death (n = 1), non-contrast CT performed due to chronic renal failure (n = 1) (Figure 3(a) and (b)).

Figure 3.

(a) Contrast enhanced CT illustrating IIA branch blood flow, prior to IIA coverage by stent graft; (b) contrast enhanced CT illustrating IIA branch blood flow, after IIA coverage by stent graft.

Most recent CT scan was performed 1.5 ± 2.1 years from operation. Imaging follow-up ranged from 0.5 to 9.0 years in our cohort. Here, endoleak was observed in eight cases (29.6%); type Ia (n = 1, 3.7%), type II lumbar artery (n = 4, 14.8%), type II inferior mesenteric artery (n = 3, 11.1%). No endoleak from covered IIA was observed. IIA thrombosis was observed in all patients who could be assessed (n = 24). Three patients could not be assessed – patient death prior to follow-up CT scan (n = 1), non-contrast CT was performed due to chronic renal failure (n = 2). AAA size decreased in the non-contrast CT scan patients, suggesting no endoleak. IIA thrombosis was observed proximal to the first IIA branch in 21 patients (77.8%), or 87.5% of cases where IIA branch patency could be assessed (Figure 3(a) and (b)). Contralateral IIA patency was assessed; we found that of the 22 patients who underwent unilateral IIA coverage, and who had contrast CT scan available, 20 patients (90.9%) had patent contralateral IIA. Findings of post-operative imaging follow-up are reported in Table 3.

Table 3.

Summary of post-operative follow-up.

First CT follow-up
Time from operation (days)	25.3 ± 20.7
Endoleak
Type Ia	3 (11.1%)
Type II
IIA	0 (0.0%)
Lumbar	3 (11.1%)
Median sacral	1 (3.7%)
Inferior mesenteric	3 (11.1%)
Type III	1 (3.7%)
IIA thrombosis
Yes	23 (85.2%)
No	2 (7.4%)
Unable to assess (patient death (n = 1), non-contrast CT (n = 1))	2 (7.4%)
Level of thrombosis
Proximal	19 (70.4%)
First branch	3 (11.1%)
AAA diameter (mm)	59.3 ± 13.5
CIA diameter (mm)	26.8 ± 10.2
Most recent CT follow-up
Time from operation (years)	1.5 ± 2.1
Endoleak
Type Ia	1 (3.7%)
Type II
IIA	0 (0.0%)
Lumbar	4 (14.8%)
Inferior mesenteric	3 (11.1%)
IIA thrombosis
Yes	24 (88.9%)
No	0 (0.0%)
Unable to assess (patient death (n = 1), non-contrast CT (n = 2))	3 (11.1%)
Level of thrombosis
Proximal	21 (77.8%)
First branch	2 (7.4%)
AAA diameter (mm)	56.5 ± 16.4
CIA diameter (mm)	26.2 ± 9.9
Contralateral IIA patency	20 (90.9%)
Range of follow-up (years)	0.5–9.0

AAA: abdominal aortic aneurysms; CIA: common iliac artery; IIA: internal iliac artery.

Complications were reported in EVAR follow-up. In-hospital death occurred in two patients (7.4%); one patient died of acute respiratory distress syndrome secondary to pneumonia, the second patient was a Jehovah’s witness with anemia who refused blood transfusion. Distal graft migration (n = 1, 3.7%), graft limb thrombosis (n = 1, 3.7%), and infection (n = 1, 3.7%) have all been reported. The distal graft migration occurred in an aortouniiliac device and was treated by proximal graft deployment. The graft limb thrombosis occurred secondary to kinking on the side where the IIA was covered. One patient underwent embolization for persistent type II endoleak from the lumbar artery. In clinical follow-up, two patients (7.4%) reported buttock claudication after walking for short distances. No severe pelvic ischemic complications such as bowel ischemia, buttock muscle necrosis, or spinal cord ischemia were observed perioperatively or in long-term follow-up. Complications are summarized in Table 4.

Table 4.

Follow-up complications.

In-hospital death	2 (7.4%)
Migration	1 (3.7%)
Thrombosis	1 (3.7%)
Infection	1 (3.7%)
Embolization for lumbar endoleak	1 (3.7%)
Buttock claudication	2 (7.4%)

Discussion

EVAR is becoming the treatment of choice for patients with abdominal aneurysms. The evolution of endografts and increased operator experience has enabled the application of this technique in treatment of patients with less favourable anatomy.^1–4 The goal of the procedure is to prevent aneurysmal expansion and rupture. Patients with aneurysmal distal landing zone in the CIA represent a therapeutic challenge. The stent graft must be extended into the EIA to exclude the aneurysm completely and prevent type I endoleaks, consequently excluding the IIA and creating the risk of pelvic ischemia.^6–9

Effective pelvic circulation is dependent on a rich network of collateral vessels between the IIAs, the IIA branches, the inferior mesenteric artery, and the femoral profunda arteries. Obstruction of this network, particularly of the large IIAs, may result in ischemic sequelae, namely buttock claudication, sexual dysfunction, spinal cord ischemia, colonic ischemia, and gluteal necrosis.^5,7,16

Interestingly, the risk of pelvic ischemia associated with IIA occlusion has been reportedly lower in the open surgical approach compared to endovascular cases where the IIA has been embolized.^17–19 These differences are likely related to IIA branch occlusion during embolization; open surgery offers the ability for more proximal IIA occlusion as well as inferior mesenteric artery re-implantation, both of which may improve pelvic collateral circulation. The implication of open surgical repair with its documented increase in perioperative morbidity and the benefits of marginal improvements in pelvic circulation likely do not outweigh the risks, especially in the context of the growing flexibility of the endovascular approach.

The optimal endovascular management of IIA in aneurysms lacking a sufficient CIA landing zone remains controversial. Three major approaches are currently employed: (1) iliac bifurcated devices, (2) pre-operative IIA embolization, and (3) simple coverage of the IIA origin. Iliac bifurcated devices, while a seemingly attractive option to maintain IIA patency, are associated with increased operative and radiation time, contrast dye injection, cost, and procedural complexity. Long-term outcomes concerning re-stenosis rates, migration, thrombosis, endoleak, and pelvic ischemic symptoms are not well studied. Furthermore, the branched design of these devices precludes deployment in patients with tortuous anatomy, and the custom nature of these devices excludes patients suffering from aneurysm rupture in need of immediate intervention.^11,13,20

The current mainstay of IIA management is the pre-operative embolization of this artery prior to coverage of its origin with the endovascular stent graft. This approach has the benefit of preventing retrograde perfusion of the CIA aneurysm sac, post-repair dilation, and rupture.^8,10 However, this approach cannot be easily employed in patients with tortuous iliac anatomy. The embolization procedure may result in long-term complications such as coil migration and vessel damage.¹⁵ Furthermore, embolization often necessitates a separate procedure and poses increased cost, operative time, contrast dye use and intra-operative radiation. Additionally, as mentioned previously, embolization leads to distal IIA branch occlusion, and this likely plays a role in the pelvic ischemic pathology that may be seen in follow-up.^5–9

Efforts to reduce the incidence of ischemic symptoms in the embolization approach have revolved around reducing the effects of sudden flow interruption to the IIA. It has been postulated that altering the timing and technique of pre-operative embolization may promote gradual thrombosis and allow for collateralization via smaller blood vessels.²¹ However, further evidence has revealed that these increases in collateral circulation occur over the course of several months, rather than over days.²² Thus, the protocol of embolization 1–14 days prior to EVAR employed in many institutions confers no benefit in reducing pelvic ischemia.

The option we describe here, IIA coverage without prior embolization, poses as a viable option in endovascular IIA management. The results of this study demonstrate that this is a safe alternative to embolization in cases where the EVAR graft limb cannot be deployed in the CIA. IIA coverage enables endovascular management in patients with tortuous anatomy. Furthermore, this approach is technically simple and cost effective, requiring only stent graft limb extensions into the EIA.

The primary concern with this approach has been the possibility of type II endoleak via the IIA, retrograde perfusion, and subsequent aneurysm dilation and rupture. The present investigation demonstrates no endoleaks of the IIA origin throughout the duration of the follow-up period. The primary benefit conferred by this method over embolization is the reduced frequency and severity of pelvic ischemic symptoms. Previous investigators have speculated the role of pelvic vascular collateralization in the physiology underlying this phenomenon.^21–23 To this end, in this investigation, we have demonstrated two major findings on most recent CT imaging follow-up: (1) 100% IIA thrombosis, (2) first IIA branch patency in 87.5% of cases. These findings confirm the benefits of IIA coverage over embolization. First that simple coverage leads to sufficient thrombosis and occlusion of the IIA orifice to prevent type II endoleaks and second that in the majority of cases this thrombosis occurs proximally, consequently preserving collateral pelvic flow and likely improving clinical ischemic outcomes. Consistent with this, perioperative reports demonstrate no manifestations of pelvic ischemia, spinal cord ischemia, ischemic colitis, or gluteal necrosis. However, clinical follow-up did reveal symptoms of buttock claudication in two patients.

In terms of complications, overall we demonstrate that the IIA coverage approach is relatively safe. The majority of procedure-related complications encountered in this cohort were not consequences of extending the stent graft limbs into the EIA. Frequency of each complication – in-hospital death, migration, thrombosis, infection, persistent lumbar endoleak – was relatively low, and was likely related to the baseline aneurysm morphology, patient physiology, and was typical of the standard EVAR.^1–4

The exception to this is the buttock claudication revealed in two patients (7.4%) during clinical follow-up. One of these patients underwent bilateral IIA coverage, and had thrombosis up to the level of the first IIA branch. The other patient underwent unilateral IIA coverage, and the first IIA branch was patient. Previous investigations have reported the incidence of post-operative buttock claudication in the range of 0% to 30%.^6,8,9,24,25 Typically, this complication is transient; persistent buttock claudication is uncommon. Comparative trials have revealed the incidence of buttock claudication is higher in IIA embolization compared to IIA coverage.^9,14,15

Currently, there is reluctance in adopting this IIA coverage technique as embolization offers the operator more assurance that the IIA has been occluded and therefore a reduced risk of IIA type II endoleak. Retrograde IIA bleeding after simple coverage is certainly a theoretical possibility, especially over a long period of time. While small trials like ours refute this claim, significant long-term follow-up is lacking. Part of the problem is that the traditional patients with AAA are elderly vasculopaths with significant comorbidities often limiting life span. However, as endovascular aortic grafts are deployed in an increasingly younger population of patients, long-term follow-up will become easier to determine and more important to consider.

Limitations

This investigation was limited by its single surgeon, retrospective design, and relatively small sample size. Due to the retrospective nature of our cohort, pelvic symptoms could not be systematically assessed in follow-up. Further, prospective trial with clear selection criteria for IIA coverage, as well as systematic follow-up and functional ischemic assessment is warranted.

Conclusion

Crossing the IIA during EVAR, without prior embolization is a viable treatment option for aneurysms wherein the stent graft must be landed distal to the CIA. Further prospective investigation is warranted to better evaluate both the clinical consequences of this operative technique, and its performance against the alternatives of IIA embolization and iliac branch grafts.

Footnotes

Acknowledgements

This study was presented as a poster at the 37th Annual Meeting of the Canadian Society for Vascular Surgery, Victoria, British Columbia, Canada, 25–26 September 2015.

Declaration of conflicting interests

The author(s) declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

Funding

The author(s) received no financial support for the research, authorship, and/or publication of this article.

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