Endovascular aneurysm repair (EVAR) is increasingly being used to treat abdominal aortic aneurysms (AAAs). For AAAs with a complex iliac anatomy, such as a short common iliac artery (CIA) or an aneurysmal change in the CIA, the stent graft must be extended to the external iliac artery (EIA) to obtain an adequate landing zone. This is common in EVAR [1]. However, it interrupts internal iliac artery (IIA) flow and is generally combined with IIA embolization to prevent type 2 endoleaks. Additionally, IIA embolization was performed during EVAR for isolated CIA and/or IIA aneurysms [2].

Although IIA embolization is considered a relatively safe procedure, the abrupt interruption of IIA flow is associated with pelvic ischemic complications such as buttock claudication, colonic ischemia, spinal cord ischemia, gluteal compartment syndrome, and sexual dysfunction [3].

To avoid serious complications, the preservation of flow to at least one IIA is currently recommended [4]. However, the reported incidence of pelvic ischemic complications varies and the risk factors remain unknown [3]. Therefore, this study aimed to investigate the incidence and risk factors for pelvic ischemic complications after IIA interruption during EVAR.

This study was approved by the Institutional Review Board (IRB) of Kyungpook National University Hospital (IRB No. 2022-07-001), which waived the requirement for informed consent due to the retrospective nature of the study. Between March 2006 and January 2022, 316 patients underwent endovascular treatment for aneurysms or pseudoaneurysms of the abdominal aorta or iliac arteries. IIA embolization during EVAR was performed in 78 patients (24.7%). All but one patient underwent unilateral embolization. One patient was scheduled to undergo rectal cancer surgery after EVAR underwent simultaneous bilateral embolization.

Coils or vascular plugs were used for embolization according to the patient’s anatomy and surgeon’s preference. We attempted to embolize only the proximal main trunk of the IIA to preserve the pelvic collaterals unless the IIA itself was diseased (Fig. 1). In 10 patients (3.2%), the origin of the IIA was covered with a stent graft without embolization. There were six intentional coverages, one cannulation failure, and three endograft misplacements. IIA flow preservation procedures were attempted in 42 patients (13.3%), including the iliac branch device (IBD), sandwich technique, and IIA transposition or bypass. In one patient in whom IBD deployment failed, conversion to bypass surgery occurred during the procedure. Technical failure or early graft occlusion, as detected by the one-month follow-up computed tomography (CT), occurred in five patients. Finally, 93 patients with IIA interruption were enrolled in this study (Fig. 2).

Figure 1. Internal iliac artery (IIA) embolization. (A) An IIA main trunk proximal to the bifurcation was embolized with a vascular plug (arrowhead). (B) Each of the three branches from the IIA aneurysm was embolized with coils (arrows).

Figure 2. Flow diagram demonstrating patient selection. EVAR, endovascular aneurysm repair; IIA, internal iliac artery.

The patients’ medical records and imaging studies were reviewed retrospectively. The development of buttock claudication, ischemic colitis, and spinal cord ischemia (postoperative ischemic complications) was also investigated. Buttock claudication was determined based on the patient’s subjective complaints by asking questions during an outpatient visit without an objective treadmill test. Routine colonoscopy was not performed to detect ischemic colitis unless the patients were symptomatic. To identify the risk factors for ischemic complications, univariable analysis using the chi-square test and Fisher exact test, and multivariable analysis using a binary logistic regression model were performed. The IBM SPSS Statistics 20 (IBM Corp.) was used to analyze the data. P-values of <0.05 were considered statistically significant.

The mean age of the participants was 75.8 years (range:54-92 years), and males accounted for 77.4% of the study population. The other comorbidities are presented in Table 1. Table 2 presents the angiographic findings and procedural details. Isolated iliac artery aneurysms and ruptured or pseudoaneurysms accounted for 41.9% and 5.4% of the cases, respectively. Occlusion of the inferior mesenteric artery (IMA) origin was confirmed in 15.1% of the cases on preoperative CT. Therefore, the postoperative IMA patency rate was 14.0%, excluding 66 patients with IMA interruption due to an aortic endograft. IIA branch embolization was performed in 19.4% of the patients. As five patients had contralateral IIA occlusion before the procedure, six patients did not have at least one patent IIA postoperatively.

Table 1 . Patient demographic data.

Demographic data	Value (n=93)
Age (y)	75.8±7.80 (54-92)
Age ≤80 y	68 (73.1)
Sex, male	72 (77.4)
Smoking	47 (50.5)
Hypertension	63 (67.7)
Diabetes mellitus	22 (23.7)
Chronic kidney diseasea	27 (29.0)
Coronary artery disease	31 (33.3)
Cerebrovascular disease	24 (25.8)
Chronic obstructive pulmonary disease	26 (28.0)
Hyperlipidemia	39 (41.9)

Values are presented as mean±standard deviation (range) or number (%)..

^aEstimated glomerular filtration rate <60 mL/min/1.73m²..

Table 2 . Angiographic findings and procedure details.

Findings and procedure details	Value (n=93)
Site of aneurysm
Abdominal aorta with or without iliac artery	54 (58.1)
Isolated iliac artery	39 (41.9)
Ruptured	2 (2.2)
Pseudoaneurysm	3 (3.2)
Preoperative IMA occlusion	14 (15.1)
IMA interruption	66 (71.0)
Postoperative IMA patency	13 (14.0)
Type of IIA interruption
Embolization	78 (83.9)
IIA main trunk	60 (64.5)
IIA branches	18 (19.4)
Without embolization	15 (16.1)
Preoperative contralateral IIA occlusion	5 (5.4)
Postoperative bilateral IIA occlusion	6 (6.5)

Values are presented as number (%)..

IMA, inferior mesenteric artery; IIA, internal iliac artery..

With regard to postoperative ischemic complications, no clinical manifestations of ischemic colitis or spinal cord ischemia were observed. Buttock claudication occurred in 30 of the 92 patients (32.6%); however, one patient (who was bedridden) was not able to confirm the presence of this symptom.

According to univariable analysis (Table 3), the incidence of buttock claudication was significantly higher among patients aged ≤80 years (P=0.038) and those with isolated iliac artery aneurysms (P=0.011). However, postoperative IMA patency, IIA branch embolization, and postoperative bilateral IIA occlusion were not significantly associated with buttock claudication development. According to the multivariable analysis using the binary logistic regression model, both age ≤80 years and isolated iliac artery aneurysm were identified as independent risk factors for buttock claudication (Table 4).

Table 3 . Univariable analysis of the risk factors for buttock claudication (n=92).

Variable	Buttock claudication (–) (n=62)	Buttock claudication (+) (n=30)	P-value
Age ≤80 y	41 (66.1)	26 (86.7)	0.038
Sex, male	48 (77.4)	24 (80.0)	0.778
Smoking	34 (54.8)	13 (43.3)	0.301
Hypertension	43 (69.4)	20 (66.7)	0.795
Diabetes mellitus	14 (22.6)	8 (26.7)	0.667
Chronic kidney disease	19 (30.6)	8 (26.7)	0.694
Coronary artery disease	20 (32.3)	10 (33.3)	0.918
Cerebrovascular disease	15 (24.2)	9 (30.0)	0.552
Chronic obstructive pulmonary disease	17 (27.4)	9 (30.0)	0.797
Hyperlipidemia	26 (41.9)	12 (40.0)	0.860
Isolated iliac artery aneurysm	20 (32.3)	18 (60.0)	0.011
Ruptured	2 (3.2)	-	>0.999
Pseudoaneurysm	3 (4.8)	-	>0.999
Preoperative IMA occlusion	11 (17.7)	3 (10.0)	0.537a
IMA interruption	42 (67.7)	23 (76.7)	0.378
Postoperative IMA patency	9 (14.5)	4 (13.3)	>0.999a
IIA branch embolization	14 (22.6)	4 (13.3)	0.295
Postoperative bilateral IIA occlusion	3 (4.8)	3 (10.0)	0.387a

Values are presented as number (%)..

IMA, inferior mesenteric artery; IIA, internal iliac artery..

^aFisher exact test..

Table 4 . Multivariable analysis of risk factors for buttock claudication.

Variable	Odds ratio	95% Confidence interval	P-value
Age ≤80 y	3.663	1.056-12.821	0.041
Isolated iliac artery aneurysm	3.867	1.428-10.472	0.008
IMA interruption	2.442	0.794-7.511	0.119
IIA branch embolization	0.465	0.125-1.729	0.253

IMA, inferior mesenteric artery; IIA, internal iliac artery..

Before the endovascular era, it has been known that bilateral interruption of IIA circulation can cause serious morbidities (e.g., spinal cord ischemia, ischemic colitis, gluteal necrosis, and bladder sphincteric dysfunction) and mortality in open surgical repair [5,6]. However, the consequences of bilateral IIA interruptions in EVAR are quite different, although sequential interruptions are included [7,8]. Mehta et al. [7] reported no ischemic colitis, buttock necrosis, or neurologic deficits in 32 patients who underwent bilateral IIA interruption during EVAR.

In this study, no serious pelvic ischemic complications (such as ischemic colitis or spinal cord ischemia) occurred after IIA interruption, even in patients without IIA flow on at least one side. This outcome was consistent with the findings of previous studies [8-12]. Although such complications have been reported in the literature [13-16], they are rare. Therefore, IIA embolization with preservation of contralateral IIA flow is an acceptable procedure to expand the indications for EVAR.

However, the incidence of buttock claudication in this study was relatively high (30%). The reported incidence of buttock claudication is 13%-50% [10]. In most cases, buttock claudication is tolerated and resolves with exercise regimens [3]. However, it occasionally leads to debilitating conditions and persists in a few patients [17,18]. No risk factors for buttock claudication have been identified. However, the most frequently mentioned risk factor is bilateral IIA interruption, because the pelvic cavity is mainly supplied by both IIAs, which are connected by collaterals. Therefore, some physicians advocate staged bilateral IIA interruptions to induce collateral circulation development and reduce pelvic ischemic complications [8,14]. However, clinical outcomes of this procedure vary among studies. Schoder et al. [19] reported that bilateral IIA interruptions resulted in a higher incidence of buttock claudication than unilateral interruptions (36% vs. 80%). Nevertheless, Mehta et al. [14] reported that the one-month and one-year buttock claudication rates were 36% and 12%, respectively, in the unilateral group and 40% and 11%, respectively, in the bilateral group. This inconsistent outcome is partly due to pelvic collateral circulation from the EIA and deep femoral artery (DFA) [6]. Yano et al. [20] reviewed the preoperative angiographic findings in patients with persistent clinical manifestations. They identified the following three radiologic risk factors: (1) contralateral IIA stenosis ≥70%, (2) invisible named IIA branches ≥3 with newly developed collaterals, and (3) poor ipsilateral collaterals from the DFA [20]. The second conflicting risk factor was the site of interruption. Cynamon et al. [17] analyzed sites of embolization in relation to IIA branches. Embolization distal to the IIA bifurcation resulted in a higher buttock claudication rate than embolization of the main IIA proximal to the IIA bifurcation (55% vs. 10%). Interruption of the proximal IIA can save the pelvic collaterals, whereas branch artery embolization might interrupt these collaterals. Kritpracha et al. [21] also emphasized the importance of proximal IIA embolization in preventing pelvic ischemic symptoms (13% for proximal embolization vs. 75% for distal embolization). However, in some studies, IIA branch embolization was not associated with buttock claudication [16,18]. Lyden et al. [16] analyzed 23 patients who underwent IIA embolization; buttock claudication was observed in four of nine patients (45%) who underwent proximal embolization and five of 15 patients (33%) who underwent distal embolization. Rhee et al. [18] analyzed a cohort of 49 patients who underwent IIA interruption and found no correlation between the location of IIA occlusion (e.g., proximal or distal coil embolization or direct surgical ligation) and reported claudication symptoms. Regarding demographic data, Farahmand et al. [22] reported that diabetes (OR=0.127, CI=0.022-0.724) and age (OR=0.925, 95% CI=0.877-0.976) were independent predictive factors of buttock claudication. Younger patients are more likely to experience buttock claudication because younger patients are more active and older patients are less active; thus, the incidence of this condition might be underestimated among older patients. The reason patients with diabetes are less likely to experience buttock claudication is unclear; however, the authors hypothesized that this was because they were less active [22].

In our study, youthfulness was identified as an independent risk factor; however, diabetes was not associated with buttock claudication. Because there was only one case of bilateral IIA interruption owing to our treatment policy, we were unable to compare unilateral interruption with bilateral IIA interruption. Nevertheless, we focused on the angiographic findings, including preoperative IMA patency, IMA interruption, postoperative IMA patency, and IIA branch embolization. We did not analyze the collaterals from the DFA because the majority of angiography images did not include the femoral bifurcation. None of them were associated with buttock claudication, and we failed to identify a new angiographic risk factor. Interestingly, isolated iliac artery aneurysms were associated with a higher buttock claudication rate than AAA after IIA interruption. However, the reason for this observation remains unclear. Because the primary etiology of AAA is degenerative and closely related to atherosclerosis [23], we hypothesized that isolated iliac artery aneurysms might be more associated with atherosclerotic changes in the pelvic vessels, which means there may be fewer collaterals.

The most common ischemic complication after IIA interruption is buttock claudication (32.6%); however, critical complications such as ischemic colitis or spinal cord ischemia are rare, even in bilateral IIA occlusion. The independent risk factors for buttock claudication after IIA interruption are age ≤80 years and isolated iliac artery aneurysm. Therefore, IIA interruption can be safely performed during EVAR and adjunctive procedures to preserve blood flow to both IIAs and should be selectively considered for active young patients.

This study has several limitations. First, this was a retrospective study; thus, we could not collect data on symptom severity and symptom improvement. In addition, no objective tests, such as the treadmill test, were performed to check for buttock claudication or maximal walking distances.

None.

Hyung-Kee Kim has been the editor-in-chief of the VSI since 2023. Woo-Sung Yun has been the senior editor of the VSI since 2023. They were not involved in the review process. Otherwise, no potential conflict of interest relevant to this article was reported.

Concept and design: WSY. Analysis and interpretation: HJK, WSY. Data collection: all authors. Writing the article: HJK, WSY. Critical revision of the article: all authors. Final approval of the article: all authors. Statistical analysis: HJK, WSY. Obtained funding: none. Overall responsibility: WSY.