Endovascular aneurysm repair (EVAR) is generally a safe and efficient treatment (1, 2, 3). However, as the anatomy of abdominal aortic aneurysm and aneurysmal dilatation of iliac arteries are complex at times, a variety of bifurcated or aorto-uniiliac stent grafts are used to provide an adequate proximal aortic neck length and diameter (1). In the case of short or aneurysmal common iliac arteries, extension of the stent graft into the external iliac artery is required in order to achieve safe positioning and sealing (1, 2). Also, an ipsilateral internal iliac artery embolization is generally necessary to prevent retrograde blood flow and potential endoleaks (1, 2). Internal iliac embolization using conventional pushable coils has been proposed as a standard procedure (1, 4, 5). Although conventional pushable coil embolizations generates thrombosis to provide collateral flow among the distal branches, precise performance of conventional pushable coil embolization of the internal iliac artery may be difficult due to coil migration or placement into more distal internal iliac artery branches (1, 4, 5). An imprecise conventional pushable coil embolization may lead to buttock claudication, sexual dysfunction, and ischemia after occlusion of the internal iliac arteries (4, 5, 6, 7). The Amplatzer vascular plug (AVP) is another embolization device. The AVP provides the advantage of precise positioning. However, the AVP does not have an over-the-wire capability, so a long guiding catheter is needed for advancement; and sometimes, tortuous internal iliac artery could not be selected for AVP embolization (8).

The purpose of this study was to evaluate the effectiveness of a 0.018-inch detachable interlock microcoil (Boston Scientific, Natick, MA, USA) for embolization of the internal iliac artery during an EVAR procedure, in order to overcome the disadvantages associated with the use of a conventional pushable coil embolization.

Findings on preprocedural CT angiographies of all patients revealed six cases of type D abdominal aortic aneurysm and seven cases of type E abdominal aortic aneurysm. Internal iliac artery embolization was left-sided in nine patients and right-sided in four patients. All internal iliac artery embolization procedures were performed during the EVAR. The mean number of detachable interlock microcoils used for internal iliac artery embolization was 4.15 (range: 2-9, size: 5-14 mm) (Table 1). Internal iliac artery embolizations were performed successfully in all 13 patients. Intraoperative angiograms confirmed vessel occlusion in all 13 patients, who had undergone perioperative embolization, and accurate embolization of the neck of the internal iliac artery before the first branch vessel in all 13 patients to our original intention. Two examples of embolization in patient 1 and patient 2 are shown in Figures 1, 2. Various lengths and diameters of detachable interlock microcoils were deployed as a tailored approach to the occlusion of the internal iliac artery. The median clinical follow-up period was 12 months (range, 1-27 months). The median imaging follow-up period was 3 months (range, 1-27 months). Postprocedural follow-up imaging was available variably across the patients as follows: at 1 month after the procedure for 3 patients (patient 7, 11, and 12), at 3 months for 4 patients (patient 3, 6, 8, 10), at 6 months for 3 patients (patient 1, 5, 13), at 12 months for 1 patient (patient 9), at 26 months for 1 patient (patient 4), and at 27 months for 1 patient (patient 2). CT angiographies were used for all postoperative imaging. Neither retrograde perfusion of the aneurysm sac nor endoleak related to the detachable interlocking coil was observed on CT angiographies in any patient. Two examples of follow-up imaging of patient 1 and patient 2 are shown in Figures 3, 4.

Clinical side effects attributed to a detachable interlock microcoil embolization were documented in two patients (15%). One patient reported of severe pain in both buttocks (especially the left embolization side) immediately after the embolization. However, this patient reported of continuous improvement of symptoms at three-month follow-up.

Another patient reported of mild right buttock pain immediately after the embolization. However, the pain had nearly disappeared by the three-month follow-up. None of the patients reported of bowel ischemia or sexual dysfunction. One patient died due to underlying stomach cancer during the follow-up period. There were no minor complications such as nausea, vomiting, and groin hematoma or major complication such as coil migration, bleeding, sepsis, or death.

Anatomic feasibility of EVARs has been reported to be between 10% and 80% (13, 14). An aneurysmal dilatation of the iliac artery can prevent safe anchoring of the distal graft. In our trial, all patients with an abdominal aorta aneurysm were selected to receive internal iliac artery embolization on the basis of the special anatomy of the common iliac arteries. All patients had an accompanying aneurysmal common iliac artery with extension into the iliac bifurcation, which did not allow sufficient distal stent-graft sealing. Because the anatomy of these patients required elongation of the stent-graft into the external iliac artery, an internal iliac artery embolization was compulsory to prevent retrograde perfusion and potential endoleaks.

In the past, the standard strategy most oftenly recommended included an internal iliac artery embolization using a conventional pushable coil to prevent endoleaks and potential reflux (1, 4, 5). The effectiveness of conventional pushable coils for the occlusion of an artery has been established beyond any doubt (15). In general, conventional pushable coil embolization of the internal iliac artery is a safe approach that can result in a significant increase in the applicability of an EVAR (4, 5). The initial technical success rate of the conventional pushable coil embolization was about 95% (16). However, precise embolization of the internal iliac artery using the conventional pushable coil may be difficult due to coil migration or placement into more distal internal iliac artery branches. Therefore, inaccurate coil embolization may lead to buttock claudication, sexual dysfunction, and ischemia after occlusion of internal iliac arteries (5, 7). Park et al. (17) reported an internal iliac artery embolization with coils associated EVAR that can lead to ischemic complication such as buttock claudications. Also, a conventional pushable coil cannot be repositioned once it has been discharged into the blood vessels. Therefore, the released coil cannot be retracted when it shows instability in a blood vessel (18). A nontarget coil embolization risk was reported to be 9-23% (19, 20). Ischemic complications after conventional pushable coil embolizations are quite common, and the severity ranges from buttock claudication or erectile dysfunction to colonic perforation or gluteal necrosis. Buttock claudication is the most commonly reported, from 12% to 58%; and the erectile dysfunction has been reported at 0% to 20% (2, 21, 22).

Controlled-release coils such as the detachable interlocking microcoils have been developed in an effort to overcome this major limitation of conventional pushable coil embolization (23). With the detachable interlock microcoils, a mechanical joining is made between the coil and its pusher wire (11). If the junction of the distal end of the pusher wire and the proximal end of the coil interlock is within the microcatheter, the coil can be freely advanced or recovered; only when it is beyond the tip of the microcatheter dose the coil mechanically detaches. Just after a detachable interlock microcoil has been released from the tip of the catheter, the coil has detached itself. This mechanism supports the placement of detachable interlock microcoils at a desired location before being totally discharged (11). As with this mechanism, we successfully embolized the internal iliac artery avoiding coil migrations. Although the number of patients receiving the conventional pushable coil embolization in our hospital was small, the ratio of postembolization ischemic complications (50%) was greater than that of the patients receiving the detachable interlock microcoil (15%). These complications were improved during the follow-up period. Reidy and Qureshi (11) reported on the use of detachable interlock microcoils in situations where the use of conventional pushable coil embolization techniques was considered unsafe. In this study, control of the coil and its discharge were acceptable, and all coils were fully retrievable up to the point of deployment (11). From these results, the investigators inferred that the coil is an effective device that allows the performance of controlled embolization (11). Also, Dudeck et al. (24) compared embolization of the gastroduodenal artery before selective internal radiotherapy for alleviation in primary and secondary liver tumors using the conventional pushable coil with the detachable interlock microcoil. The detachable interlock microcoil was associated with a shorter procedure time, lower radiation dose for coil deployment, and lower coil number than the conventional pushable coil (24). Also, endovascular detachable coil embolization could be an effective treatment for renal artery aneurysms (25). Even difficult renal artery aneurysm cases such as a wide-necked or bifurcations could be successfully treated by the detachable interlock coil (25).

Some investigators have reported success with the use of AVPs in internal iliac artery embolizations before endovascular repair of aortoiliac aneurysms (2, 8). Precise positioning and cost saving are the advantages of the AVP, compared to the coils. There are no reports of initial technical failure of AVPs embolization in the literature (2, 8, 26). However, there are some reported cases of the need for additional coils or a secondary device deployment (16). Also, the AVP does not have an over the wire capability, therefore, a long guiding catheter is needed for the forward motion of the AVPs. As a consequence, progression of the AVPs through the long guiding catheter may be blocked, and sometimes, tortuous internal iliac artery could not be selected for AVP embolization (8). Meanwhile, recently launched AVP 4 (AGA Medical Corp., Plymouth, MN, USA) is accessible with the diameters of 4-8 mm. The advantages over the previous vascular plug is that it may be easier to move through tortuous vasculature and there may be no need for sheath or guiding catheter exchange (27). However, the AVP 4 can be used to embolize the small internal iliac arteries of less than 6.5 mm in diameter. In our study, most cases (12 cases, 92%) had diameters greater than 6.5 mm, so these were not suitable for the AVP 4. The AVP 4 was launched in Korea in late 2012, but our procedures were done between 2010 and 2012; so, we were unable to use the AVP 4. Buttock claudication rates of AVPs embolization are reported in 9% to 33% of the cases, and erectile dysfunctions were essentially unreported (2, 8, 16, 26). Libicher et al. (28) reported that embolization of internal iliac arteries with either coils or AVPs was safe and effective. Initial buttock claudication was more severe with coils, but there was no significant difference after 12 months of follow-up (28). AVPs embolization is connected with a significant reduction of procedure time and radiation dose compared to coils (28).

In our detachable interlock microcoil study, buttock pain occurred in two patients (15%). Buttock claudication is the most common ischemic complication after interruption of the internal iliac artery. Schoder et al. (1) reported a greater ratio of postembolization buttock claudications when coils were placed in (47%) versus above (20%) of internal iliac artery bifurcation. Also in ischemic complications of our conventional pushable coil embolizations, the coils were located inaccurately in the internal artery bifurcation. Some reported that the majority of milder buttock claudication improved over time with conservative treatment such as that in our patients (29, 30, 31).

We embolized the internal iliac artery before the first branch. Therefore, the ratio of postembolization buttock pain was small and the patients' symptoms showed improvement at the three-month follow-up. Therefore, precise positioning of the coils was critical in preventing buttock caludication or other complications. In most patients, the intricate network of collateral vessels of the pelvis compensated for ischemic complications of embolization of the internal iliac arteries (29).

This study had limitations. First, the sample size is small, which prevents us from making generalizations on the basis of the results of this study. Second, this series is consecutive and lacks randomization; therefore, patient selection bias may have played a role. A prospective randomized trial would be beneficial in order to define the exact value and clinical outcome of internal iliac artery embolization using detachable interlock microcoils compared to conventional coils. Third, the follow-up interval was short and uneven.

In conclusion, internal iliac artery embolization during an EVAR using detachable interlock microcoils to prevent type II endoleaks appears safe and effective, although this should be further proven in a larger population.