Abstract
The aim of the paper is to evaluate the outcome of endovascular treatments for isolated internal iliac artery aneurysms. A systematic review of the literature using public domain databases was undertaken. All studies reporting on endovascular treatment of isolated hypogastric artery aneurysms were considered. Experience from our institution was involved in the data analysis. The primary outcome measures were technical success, perioperative, and overall mortality and morbidity. Data were extracted from 30 articles fulfilling the selection criteria, and the study cohort consisted of 55 patients having undergone treatment of 59 internal iliac artery aneurysms. Ten patients (18%) were treated on an urgent or emergency basis for a ruptured aneurysm. Technical success was achieved in 71% of the cases. The most common reason for technical failure was incomplete exclusion of the aneurysm sac. Thirty-day mortality occurred in one patient (2%). The 30-day morbidity rate was 20%, and was mostly associated with insufficiency of the pelvic circulation. One aneurysm-related death occurred during a mean follow-up period of 13 months (range 0.5–56 months). Open surgical intervention for aneurysm-related complications was required in five patients. In conclusion, endovascular treatment of isolated internal iliac artery aneurysms is an effective alternative option, with satisfactory early and mid-term results.
Introduction
Isolated aneurysms of the internal iliac artery constitute an important subset of aortoiliac aneurysms. Even though they are an uncommon condition, comprising 0.4% of all intra-abdominal aneurysms, they are clinically significant because of their anatomical position deep within the pelvis, elusive clinical presentation and diagnosis, and the risk of rupture. 1,2 Their natural course is not well defined because of the lack of large prospective series describing their natural history; however, it has been demonstrated to be one of continuing enlargement and rupture, which is associated with significant mortality. 3,4 With the widespread use of advanced medical imaging, internal iliac artery aneurysms are increasingly diagnosed at an asymptomatic stage, and given their serious prognosis following rupture, early repair of aneurysms with a diameter greater than 3 cm is advocated. 5,6
For many years, open surgical repair, consisting of either ligation of the internal iliac artery alone or in conjunction with endoaneurysmorrhaphy, or aneurysm resection, has conventionally been the mainstay treatment. The associated mortality of surgical reconstruction remains high, mainly because of restricted access to deeply located aneurysms and difficulties achieving hemostatic control of branching pelvic vessels. 7 Catheter-based interventions and endovascular treatments have emerged as an alternative less invasive therapeutic tool, which is of particular significance in an elderly population with atherosclerotic aneurysms and cardiovascular co-morbidities. 8,9 We had the occasion to treat a frail patient with bilateral internal iliac artery aneurysms, who presented with rupture, with endovascular stent graft repair. Although endovascular technology has been successfully employed for the exclusion of internal iliac artery aneurysms, the clinical evidence evaluating the efficacy of this method and quantifying the advantages over conventional surgical treatment is not well reported.
On the occasion of the case treated in our center, a systematic review and analysis of the literature was undertaken to identify the published evidence and evaluate the outcomes and prognosis after endovascular treatments for isolated internal iliac artery aneurysms.
Methods
A systematic search of the literature was undertaken to identify articles reporting on endovascular treatment of isolated internal iliac artery aneurysms. Public domain databases (MEDLINE) were searched electronically using a web-based search engine (PubMed) for articles published between 1966 and November 2010. The MeSH terms/keywords ‘iliac artery’, ‘iliac aneurysm’, ‘endoluminal repair’, ‘therapeutic embolization’ and ‘stent’ in all possible combinations were applied to detect relevant articles. Related articles suggested by the PubMed search engine and reviews on this area were further searched for any additional relevant articles. A second-level search included manual search of the reference lists of the retrieved articles. The literature search, study selection and data abstraction were independently performed by two authors.
Articles reporting on endovascular treatment of isolated aneurysms of the internal iliac arterial system of atherosclerotic etiology were considered for inclusion in data synthesis and analysis. Patients with previous open or endovascular treatments of aortoiliac aneurysms who subsequently developed aneurysms of the internal iliac artery were also included. Case reports and patient series providing adequate details regarding the endovascular procedure and the outcome, as expressed by the technical success and the postoperative morbidity and mortality of the individual patients, were included in the analysis. Technical success was defined as successful completion of the endovascular procedure, without evidence of residual blood flow into the aneurysm on intraoperative or early postoperative imaging, obviating the need for open surgical conversion. The study endpoints were defined as early outcome, expressed by the technical success and 30-day morbidity and mortality, and late outcome depicted in morbidity and mortality rates during follow-up.
Patient data parameters abstracted and considered for further analysis included age, sex, aneurysm size, site of the aneurysm, treatment of unilateral or bilateral aneurysms, presence of rupture and presenting symptoms, previous repair of aortoiliac aneurysm, specific endovascular treatment received, technical success, 30-day morbidity and mortality, duration of follow-up and events on follow-up, including late morbidity and mortality. Data retrieved from each paper were entered into a purpose-designed database using SPSS 15 for Windows (SPSS Inc, Chicago, IL, USA). Simple descriptive statistics were applied to perform the pooled analysis and calculate the overall outcome measures. Data are presented as means and ranges. The χ 2 test was used to evaluate outcome differences in subgroups of patients having received different endovascular treatments.
Results
Literature search results
Search of the medical literature identified 53 articles reporting on endovascular treatments for internal iliac artery aneurysms, the full texts of which were retrieved and thoroughly appraised. Thirty articles specifically reviewed patients with isolated atherosclerotic hypogastric aneurysms and provided adequate individual patient data to be eligible for entry into the analysis of the present study. 10–39 They were either case reports or small retrospective case series. No comparative trials of conventional open surgical and endovascular internal iliac artery aneurysm repair were encountered.
Patient characteristics
The selected articles reported on a total of 54 patients. Another patient with bilateral internal iliac artery aneurysms with a rupture on the left was urgently managed with endovascular stent graft repair in our institution and was included in the overall analysis, yielding a study group consisting of 55 patients. The demographic and clinical characteristics of the study population are outlined in Table 1. The majority (96%) of the patients were men (53 men, 2 women), and the mean age was 75 y (range 45–92 y). The site of the aneurysm was the left and right internal iliac artery in 23 and 21 patients, respectively, whereas bilateral aneurysms were found in six patients (11%); the site of the aneurysm was not reported in five patients. The mean aneurysm diameter was 6.1 cm (range 3–14 cm). Ten patients (18%) were treated on an urgent or emergency basis for a ruptured internal iliac artery aneurysm. All these patients presented with abdominal pain and the rupture was documented on preoperative imaging (computed tomography, CT). The presenting symptomatology was not defined in 12 patients. In most of the remaining cases (21/43, 49%), the internal iliac aneurysm was an incidental finding either during investigations for another intra-abdominal pathology or on imaging follow-up after previous aortoiliac aneurysm reconstruction. For those who developed symptoms, the most common presentation was lower abdominal, low back or buttock pain (17/43, 40%), whereas in five patients (5/43, 12%), the presenting clinical picture resulted from compression of the adjacent iliac venous system and consisted of lower limb edema and/or deep vein thrombosis.
Baseline demographic and clinical characteristics
DVT, deep vein thrombosis; UTI, urinary tract infection; NR, not reported; L, left; R, right
Procedures and outcome
The primary endovascular procedure consisted of coil embolization of the aneurysm outflow vessels (distal embolization), aneurysm sac itself and/or the aneurysm neck (proximal embolization) in the majority of the reported cases (51 patients, 93%). In 15 patients, coil embolization was accompanied by a separate procedure, which included deployment of a stent graft across the origin of the internal iliac artery or placement of an Amplatzer vascular plug (AGA Medical Corp, Plymouth, MN, USA) into the aneurysm neck in order to complement exclusion of antegrade blood flow into the aneurysm sac. Stent graft alone to interrupt the circulation within the hypogastric artery was used in three patients (Table 2). One patient with a previous aorto-bifemoral bypass was managed with a flexible endoprosthesis (Hemobahn, W L Gore and Associates, Flagstaff, AZ, USA) implanted into the internal iliac artery distally and the external iliac artery proximally, in order to maintain pelvic arterial flow. In another two patients with previous aortic bifurcated grafts, coil embolization was accomplished through the gluteal artery and percutaneous CT-guided access, respectively. In three patients, the common or external iliac artery was occluded after coil embolization of the hypogastric aneurysm and the circulation to the ipsilateral leg was restored with a femoro-femoral crossover graft (Table 3).
Outcome of different endovascular procedures
Outcome after endovascular repair of isolated internal iliac artery aneurysms
IIAA, internal iliac artery aneurysm; L, left; R, right; SFA, superficial femoral artery; CIA, common iliac artery; MI, myocardial infarction; GI, gastrointestinal; NA, not applicable; NR, not recorded; EIV, external iliac vein; EIA, external iliac artery; PE, pulmonary embolism; CT, computed tomography; ABF, aorto-bifemoral, PTFE, polytetrafluoroethylene
Technical success was achieved in 71% of the cases (39 patients). The most common reason for technical failure (11/16, 69%) was incomplete exclusion of the internal iliac artery with residual filling of the aneurysm sac, which was demonstrated either on completion angiogram or on early postoperative imaging (CT or ultrasound scan). The endoleak was initially treated conservatively in all these cases. In one patient, technical failure was caused by unsuccessful deployment of the stent graft across the origin of the internal iliac artery, which resulted in incomplete exclusion of the aneurysm; the external iliac artery was ligated and the blood supply to the limb was restored with a femoro-femoral bypass graft (Table 4). Mortality within the early postoperative period occurred in one patient (2%); a ruptured aneurysm in a high surgical risk patient was unsuccessfully managed with coil embolization on two separate occasions, and death was recorded to have been caused by exacerbation of pre-existing cardiac insufficiency and multiple organ failure. The early postoperative morbidity rate was 20% (11 patients), and was associated with insufficiency of the pelvic circulation resulting in buttock/thigh claudication in nine patients (9/55, 16%). Two of the patients who developed claudication symptoms had bilateral internal iliac artery aneurysms treated. In one patient, continuing compression of the external iliac vein by the aneurysm sac despite successful aneurysm exclusion was managed with Wallstent placement into the compressed segment of the iliac vein.
Reasons for technical failure
SFA, superficial femoral artery
The long-term outcome following the endovascular treatment of the internal iliac artery aneurysm was recorded for 41 patients. The mean follow-up period was 13 months (range 0.5–56 months). Nine patients (9/41, 22%) developed aneurysm-related complications during follow-up. In all of these patients, morbidity was associated with either a persistent or a new-onset endoleak, resulting in aneurysm enlargement. A new onset endoleak developed in four patients (4/41, 10%) during a mean follow-up of 15 months (range 1–24 months). Four patients (4/41, 10%) developed pressure effects on adjacent organs, including the bowel, ureter and iliac veins, and manifested with corresponding symptoms of bowel obstruction and aneurysm–rectal communication, hydronephrosis, and iliac vein thrombosis and pulmonary embolism, respectively. Open surgical intervention with proximal/distal ligation or endoaneurysmorrhaphy was performed in five patients (5/41, 12%), whereas one patient was managed with percutaneous transosseous injection of Gelfoam and thrombin to achieve thrombosis of the aneurysm and obliteration of the blood flow within the sac. Four patients died during the follow-up period, with one death only being related to the aneurysm and its previous endovascular treatment, yielding a late aneurysm-related mortality rate of 2% (Table 3).
Discussion
Even though aneurysms of the internal iliac artery are commonly encountered in conjunction with aortoiliac aneurysms, isolated aneurysms affecting the hypogastric artery represent a rare clinical condition with a reported prevalence of less than 0.03%. 40,41 They constitute chronic degenerative conditions, most frequently of atherosclerotic etiology, which usually occur in an elderly population with a male predominance. 6,7,42 Their clinical importance is defined by their anatomical location deep in the pelvic cavity, which creates diagnostic and operative technical difficulties, as well as the unpredictable natural course and rupture risk. The challenges to conventional open surgical repair have precipitated application of innovative therapeutic strategies to confront the significant mortality associated with the disease. Previously published series reporting on all forms of isolated iliac artery aneurysms have demonstrated that endovascular repair with a combination of stent graft placement and embolization techniques is safe and effective, raising the question whether this method should be adopted as a first-line treatment in these cases. 43,44 In the absence of large series evaluating the outcomes of modern endovascular techniques for the treatment of internal iliac artery aneurysms, an analysis of published reports has been conducted and an outlining of current evidence attempted.
Open surgical techniques include exclusion of the aneurysm sac with proximal ligation alone or in conjunction with distal ligation of the hypogastric artery, formal resection of the aneurysm or proximal ligation of the artery combined with endoaneurysmorrhaphy. 45 In the rare cases of bilateral disease and in order to prevent compromise of the pelvic arterial circulation, an interposition graft may be placed. The deep location of the aneurysm in the pelvic cavity, along with peri-inflammatory tissue reaction, creates considerable difficulties with dissection and aneurysm fixation, the risks of intraoperative hemorrhage are significant, and elective mortality rates of up to 11% have been reported. In emergency cases, the mortality figures may be as high as 50%. 4,5
Endovascular techniques consist of coil embolization of the outflow aneurysm vessels and the sac itself, which in some cases is complemented by exclusion of the orifice of the internal iliac artery by deploying a stent graft along the common and external iliac arteries. In cases where the aneurysm neck anatomy is suitable, an Amplatzer vascular plug has also been successfully used to exclude the arterial inflow. This has the theoretical advantage of obviating the risks associated with stent-graft placement in unfavorable anatomies, such as kinking and graft thrombosis. Some authors have used a stent graft alone to exclude the internal iliac artery from the circulation, without embolization of the aneurysm itself or its outflow branches. No differences in the outcome, as expressed by the technical success and late complications, among the different endovascular procedures were detected (Table 2). Innovative techniques involving the use of customized tapered stent grafts, placed across the hypogastric artery origin in an ‘up and over’ maneuver through a contralateral femoral access, have been used to overcome the anatomical difficulties associated with size discrepancy between the common and external iliac artery. Furthermore, other embolization/thrombogenic materials, such as outer parts of guidewires, acrylic glue, thrombin, autologous blood clot and gelatin sponge, have been used alone or in combination with coils, in order to induce thrombosis of the aneurysm sac.
The benefits of the application of endovascular techniques in the management of internal iliac arteries are mostly associated with the minimally invasive nature of the procedures. These may be performed percutaneously under local or regional anesthesia, with minimal blood loss, operative surgical trauma and cardiovascular compromise. This is of particular importance in an elderly population with significant atherosclerotic and respiratory co-morbidities. In the cohort of the present study, no elective perioperative mortality was recorded, whereas in emergency cases treated for ruptured aneurysms the corresponding mortality figure was 10% (rupture versus non-rupture, P = 0.044). Furthermore, patient recovery from the operation and the hospital stay are significantly shortened, with a mean postintervention hospital stay of three days in the present study cohort.
Despite the clear benefits in terms of mortality compared with open surgical techniques, endovascular therapy for hypogastric aneurysms has some inherent limitations. Although treatment may successfully exclude the aneurysm from the circulation with eventual shrinkage of the residual sac, reduction of aneurysm mass is often slow and gradual, and consequently pressure effects on adjacent organs may persist for a significant time. In these cases, compressed organs may be dealt with another minimally invasive intervention, such as stenting of the iliac vein or ureter; when this is not a feasible option, an open surgical procedure consisting of ligation of the artery, endoaneurysmorrhaphy and resection of the aneurysm sac may be required. Furthermore, in cases of bilateral aneurysms, open surgical reconstruction has the theoretical option of placing an interposition graft in order to prevent ischemic complications resulting from compromise of the pelvic circulation. In the present series, although buttock and thigh claudication was the most common procedure-related complication, affecting nine patients (16%), none of the symptoms were severe enough to warrant revascularization. This is consistent with previous literature evidence showing that bilateral hypogastric artery interruptions can be accomplished with limited morbidity. 46,47 Another limitation of endovascular treatment is the risk of ongoing or new onset endoleak within the aneurysm sac, which in some cases might need further percutaneous or open surgical intervention. Therefore, even though no consensus exists regarding the time intervals and mode of follow-up, these patients should be kept under surveillance.
The aforementioned figures regarding technical success, morbidity and mortality represent the best possible outcome, because this evidence is based on case reports and small case series only. There may well be significant reporting bias, as unsuccessful outcomes with this approach would be less likely to be published. Furthermore, significant heterogeneity exists regarding the type of endovascular procedure and the materials used among the studies of different institutions, and consequently the results of the present pooled analysis should be approached with caution. Lastly, no data currently exist to support the long-term efficacy of this method.
Conclusions
Endovascular repair of isolated internal iliac artery aneurysms is an effective alternative treatment option, especially for patients with significant cardiorespiratory co-morbidities. It has clear benefits in terms of perioperative mortality over conventional open surgical repair. However, no long-term data exist, and long-term follow-up should be the aim of current endovascular registries.
Footnotes
Acknowledgments
Financial disclosure of authors and reviewers: none reported.