Abdominal aortic aneurysm (AAA) is defined as a disease with an abdominal aortic diameter of more than 3 cm or 50% greater than the normal aortic diameter (1, 2). Although endovascular aortic aneurysm repair (EVAR) has become the first choice of treatment because of its advantages of less trauma, faster recovery and lower perioperative mortality, several studies have shown that the reintervention rate of EVAR is higher than that of OSR (3–5). Endoleaks, an important cause of reintervention, is a common and unique complication of EVAR and occurs in approximately 1/3 of postoperative patients (6). Type II endoleaks (T2ELs) are caused by retrograde blood flow from the side branches of the abdominal aorta entering the aneurysm sac after excluding the aneurysm, and they are the most common type of endoleaks, with an incidence rate between 8% and 44% (7–9).

The treatment methods for T2ELs include trans-lumbar direct embolization of the aneurysm sac, embolization of the aortic branches through the superior mesenteric artery or lumbar arteries, trans-cavity embolization, and open or laparoscopic clipping of side branches (10). Postoperative reintervention of the T2EL is challenging, while intervening in the anatomical risk factors seems to be more advantageous intraoperatively. Abdominal aortic collateral artery embolization can reduce the incidence of T2ELs and the reintervention rate (11–18) and promote the reduction of aneurysms after EVAR (12, 13, 16–18), with a lower incidence of complications (12). The high anatomical risk factors for T2ELs include patent IMA and LA (16, 19, 20). In addition, the incidence of T2ELs was also associated with the internal iliac artery ranging from 0 to 3.8% (21), and some investigators believe it was related to the iliolumbar artery (21, 22). The iliolumbar artery and lumbar artery are connected through collateral circulation and can communicate with the fourth lumbar artery (23–25). However, no studies have investigated the association between the iliolumbar artery and T2ELs after EVAR. The purpose of this study was to investigate the relationship between the iliolumbar artery and T2ELs after EVAR.

The management of T2EL remains controversial in the current literature, and it has several definitions, including “early”, “late”, “persistent” and “isolated” type II endoleaks. T2ELs were observed in 10.2% of patients after EVAR (9), and 30% to 50% of these resolved spontaneously (9, 26). In a Japanese nationwide analysis, persistent T2EL was defined as T2EL detected after EVAR on initial contrast-enhanced CT and during follow-up or new T2EL not documented at the end of EVAR but reported at any point during follow-up (27). A correlation between persistent T2ELs (p-T2ELs) and late adverse events, including aneurysm sac enlargement, reintervention, rupture, and abdominal aortic aneurysm-related mortality after endovascular aneurysm repair, was demonstrated. In addition to p-T2ELs, older age, female sex, chronic kidney disease, and dilated proximal neck were associated with sac enlargement.

Wang et al. (28) analyzed 10-year follow-up results and found that T2ELs were significantly associated with aneurysm sac growth, but no association with survival was observed. The low overall survival rate in our analysis may be related to COVID-19.

Current guidelines, such as the 2019 European Society for Vascular Surgery (ESVS) guideline and Society for Vascular Surgery implementation of clinical practice guidelines, have recommended conservative management, and intervention was indicated for significant sac expansion (≥10 mm or 5 mm) (1, 29). Although reintervention for T2ELs after EVAR could achieve some clinical effects (30–32), a study (33) found that embolization procedures were generally ineffective in preventing further expansion of abdominal aortic aneurysms in patients with T2ELs after EVAR. The risk of repeated intervention after reintervention for T2ELs exists, and the key to treating T2ELs has shifted from reintervention to prevention.

Therefore, identifying risk factors for T2ELs and early intervention in high-risk patients are key to treatment. Our study found that the IMA diameter and the number of LAs were independent risk factors, which was consistent with most studies (8, 13, 22, 34). Through ROC curve analysis, this study determined the number of lumbar arteries (≥6) and the cutoff of IMA diameter (≥2.5 mm). Some studies have identified IMA ≥3 mm as a risk factor for T2ELs (11, 12).

IIA embolization has also been suggested as a risk factor for T2ELs in some studies (35, 36). They thought IIA embolization was more likely to increase the redistribution of blood flow from the lumbar arteries and IMA branches than IIA stent coverage alone. The formation of collateral circulation may also be associated with ILA. Meishi et al. (22) thought that the iliolumbar artery arising from the IIA was a major source of T2ELs. In their study, no significant impact of IIA embolization on T2ELs was observed after analyzing 375 patients. Of all 603 patients in our article, 9.8% received unilateral and 5.1% bilateral IIA embolization. The multivariate analysis showed that the different interventions for IIA were not associated with T2ELs, regardless of the IIA status. Currently, iliac branch devices are used to preserve at least one IIA. From existing studies (37, 38) and the limited evidence presented in our article, preservation of the IIA does not appear to increase the incidence of T2ELs (22).

In addition, the relationship between ILA and T2ELs has not been compared, although it has sometimes been found to be the source of T2ELs during follow-up (Figure 5). In our study, the right ILA diameter measured based on abdominal CTA was 2.31 ± 0.65 mm, and the left ILA was 2.30 ± 0.66 mm, which was similar to previous results based on human anatomy, which reported that the diameter was 2.7 ± 0.6 mm (39). We found that 28.0% of ILAs originated from the posterior of the IIA, 69.9% from the main trunk of the IIA, and 0.2% from the CIA. Kiray et al. (40) reported an average ILA diameter of 3.7 ± 0.7 mm, and Teli et al. (25) reported an average ILA diameter of 3.5 ± 0.5 mm. Koc et al. (23) reported that the ILA diameter originating from the main trunk of the IIA was smaller than that originating from the posterior branch of the IIA. In addition, the iliac lumbar artery mainly originates from the main internal iliac artery and less from the posterior branch of the IIA and CIA (25, 39, 40). This finding was similar to our study.

In the T2ELs caused by ILA, we found that ILA tended to be backward and upward, but only 2% of T2ELs were caused by ILA. There was no significant difference in the anatomical characteristics of the ILA in univariate analysis, and the right ILA diameter also showed no difference in multivariate analysis (p = 0.83). T2ELs from the IIA reported in the past are relatively rare, and the incidence of most previous report series is between 0% and 3.8% (21, 41), and no correlation was demonstrated in previous studies (22, 42). Other risk factors associated with T2ELs include chronic kidney disease, advanced age, aneurysm sac volume, and aneurysm sac thrombus volume (34, 43–46). Although our study did not find a statistical correlation between ILA and T2ELs, T2ELs caused by ILA still deserve attention.

Pre-embolization for the IMA or aneurysm sac in high-risk patients seems to be of greater benefit (14, 47, 48), and it could suppress aneurysm sac expansion and reduce the reintervention rate. A network meta-analysis (49) suggested that IMA embolization demonstrated benefits in achieving long-term aneurysm sac stability and lowering the risk of secondary surgery. Nonselective embolization of aneurysm sac side branches more effectively reduces the incidence of T2ELs, while IMA embolization alone or in combination with aneurysm sac coil embolization enhances the clinical benefits of EVAR. Sun et al. (49) analyzed whether nonselective preemptive aneurysm sac embolization could prevent T2ELs in the short and mid-term, and they interestingly found that the IMA diameter showed continuous regression in the embolization group.

However, Kontopodis et al. (50) in their meta-analysis that included four random studies, suggested that preemptive embolization confers no clinical benefits in EVAR, but their data were limited and had low certainty. Additionally, Väärämäki et al. (51) found that the strategy of routinely embolizing the IMA does not seem to yield any significant clinical benefit and should therefore be abandoned. Therefore, more standardized, and high-quality studies are needed to explore the therapeutic effects of preemptive embolization.

There are several other limitations that should be noted. The present study excluded patients with type I and III endoleaks at any time during follow-up. This may reduce the number of patients with T2ELs because some patients with T2ELs may also have type I or type III endoleaks. Another limitation is the definition of T2EL. Previous reports use various terms, such as “early”, “late”, and “persistent” T2ELs. However, we did not classify T2ELs in this study. On the one hand, there was recall bias during the telephone follow-up; on the other hand, some patients did not have regular follow-up after surgery, so the occurrence time of endoleaks was not clear.

Finally, the mode of IIA embolization was not a routine procedure and was only performed in a relatively specialized anatomical population. Aortoiliac aneurysms with insufficient distal anchor area of the common iliac artery may lead to type Ib endoleaks (52). In some aortoiliac abdominal aortic aneurysms or AAA with internal iliac aneurysms and with a short common iliac artery, stents need to extend to the external iliac artery or even embolize the ipsilateral internal iliac artery. Future studies may need to collect the anatomical characteristics of the patent lateral branches after EVAR to identify the risk factors further accurately for type II endoleaks through the changes before and after surgery.

The iliolumbar artery and the different internal iliac artery interventions may not increase the incidence of T2Els. But the number of patent lumbar arteries (≥6) and the diameter of the inferior mesenteric artery (≥2.5 mm) were independent risk factors for T2ELs. More rigorous studies are still needed to explore the risk factors for T2ELs.T2ELs was associated with the reintervention but did not affect long-term survival or increase aneurysm-related mortality after EVAR.