Iliac anatomy and the incidence of adjunctive maneuvers during endovascular abdominal aortic aneurysm repair

The significance roles of the iliac artery during endovascular aortic aneurysm repair (EVAR) include an access site for a delivery system, a sealing zone for a stent graft, a source of pelvic flow and, occasionally, a combined iliac artery aneurysm that should be treated. Therefore, iliac anatomy is a major consideration during EVAR, and challenging iliac anatomy is remains a problem despite advancements in technology and devices [1, 2]. Hostile iliac anatomy consists of a short common iliac artery (CIA), small ilio-femoral artery diameter, combined iliac artery aneurysm, and iliac tortuosity.

We analyzed iliac artery anatomy in patients with an abdominal aortic aneurysm (AAA) and investigated the types of iliac problems and adjunctive procedures associated with them during EVAR.

Proper CIA length and diameter are necessary for a safe iliac landing zone. Within Asian anatomy, the short CIA is a difficult concern [5]. In a study based in Hong Kong, mean CIA lengths were 29.9 mm on the right and 34.2 mm on the left, compared to >50 mm in Caucasians. However, mean right and left CIA lengths in our study were 52.8 and 56.3 mm, respectively, which was not different from Western data. A short CIA (<20 mm) was detected in one patient (1%, 1/74) who had bilateral short CIAs. This problem was overcome using a hybrid procedure; EIA to IIA bypass with contralateral IIA embolization. Mean CIA diameters reported from another Korean study were 41.1 and 43.2 mm [6]. Thus, all Asians do not have short CIAs, and CIA length seemed suitable in most cases.

In the EUROSTAR (EUROpean collaborators on Stent-graft Techniques for abdominal aortic Aneurysm Repair) registry, mean CIA diameter was 16.7 mm, and the rate of concomitant uni or bilateral CIA aneurysms was only 16.8% (1,269/7,554) [7]. However, 54% of our patients had a uni- or bilateral CIA aneurysm. Mean CIA diameters were 20.8 mm on the right and 18.3 mm on the left. Previous Asian studies showed similar mean CIA diameters (17.9-20.9 mm) [5, 6]. Therefore, a large CIA diameter rather than a short CIA are characteristics of Asian iliac anatomy.

Due to unsuitable CIA anatomy, including short length and large diameter, IIA embolization was the most common adjunctive procedure in this study. An iliac extension limb was deployed to the EIA after IIA embolization to prevent a type II endoleak. This is the easiest way to solve a CIA problem. Variable pelvic ischemic complications, including buttock claudication, erectile dysfunction, ischemic colitis, gluteal or perineal necrosis, and spinal cord ischemia have been reported after interrupting pelvic flow [8, 9, 10, 11, 12, 13, 14]. Thus, bilateral IIA embolization is seldom used to preserve pelvic perfusion.

We used a hybrid procedure, such as EIA to IIA bypass with contralateral IIA embolization, to overcome bilateral CIA problems. Although this additional bypass surgery enabled successful EVAR, retroperitoneal procedures are associated with greater blood loss, higher postoperative complication rates, and longer hospital stays [15]. Several methods have been introduced to treat those patients with an endovascular method, such as the bell-bottom technique, use of an iliac branch device (IBD), or a sandwich technique. The bell-bottom technique using a flared iliac stent graft is the simplest. We used this technique in 4 patients: two patients with ruptured AAA and two highrisk patients. The immediate result was good in all patients. However, there are concerns about type Ib endoleaks due to continued iliac artery enlargement [16, 17]. In a recent study, no differences in reintervention rates for type Ib or III endoleaks were observed between the bell-bottom technique and IIA embolization with stent graft extension to the EIA during a median 22 month follow-up [18]. However, long-term data on the bell-bottom technique are needed.

IBD was designed to provide both sealing and blood flow into the EIA and IIA. The technical success rate of EVAR using IBD is 85%-100% and midterm patency is about 70% [19]. However, it is not available in all countries. Recently, domestic IBD was introduced in Korea, but its clinical data is absent yet. The sandwich technique is another option, which was first reported by Lobato [20]. Midterm follow-up results of 40 consecutive cases were announced recently; the technical success rate was 100%, and the primary patency rate was 93.8% during a mean followup of 12 months [21].

We did not experience tortuosity-related complications or any difficulties positioning stent grafts. Although superstiff guidewire with an introducer catheter usually allows a delivery system to pass a tortuous iliac artery, a stent graft delivery system may occasionally not pass, which is when a brachiofemoral wire becomes useful, as it improves trackability by placing tension on the wire and controlling both ends [22]. It is called the body floss technique. Iliac tortuosity may increase the risk of arterial dissection, rupture, limb kinking, or occlusion [23, 24, 25]. Therefore, the operator should pay attention to avoid complications when iliac tortuosity is severe, although iliac tortuosity is not an absolute contraindication for EVAR.

The last iliac problem is a small diameter iliac artery. Balloon angioplasty and stent placement are the simplest methods to overcome this problem. These methods can be performed simultaneously with EVAR. An iliac conduit is a good option when these methods are insufficient to achieve adequate iliac access [26]. An iliac conduit is used to introduce a delivery system and can be used as an ilio-femoral bypass conduit after EVAR. An aggressive endovascular solution called the "internal endoconduit" technique has been introduced to avoid retroperitoneal dissection [27]. After the endograft has been introduced into the iliac artery, a controlled iliac artery rupture is created, while maintaining proximal and distal sealing. However, this technique is not recommended routinely.

We used an AUI device in patients with a narrow distal aorta. An AUI device is useful when access to only one iliac artery is available. In a large series [28], an AUI device with femoro-femoral bypass grafting resulted in a lower technical success rate (94% vs. 99%, P = 0.002), a higher perioperative complication rate (10% vs. 4%, P = 0.005), and lower 3-year primary patency (92% vs. 98%, P = 0.003) compared with those of a bifurcated device. Three-year secondary patency in the AUI group was 97%. Although it was also lower than the bifurcated device group (97% vs. 99%, P = 0.040), it seemed acceptable. Therefore, EVAR with an AUI device is a good alternative treatment option for high-risk patients with hostile iliac anatomy.

Although challenging iliac artery anatomy is a major obstacle during EVAR, supplemental endovascular or hybrid procedures can facilitate endovascular treatment under those conditions. A precise assessment of iliac anatomy with adequate instruments and techniques is crucial. In our study, a short CIA was uncommon, and a large CIA diameter was more important during EVAR in Asians.