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Vascular and Interventional Radiology |
1 From the Departments of Radiology (A.J.T., R.R., M.M.) and Vascular Surgery (R.L., M.M., P.L.), New York University School of Medicine, Tisch Hospital, 560 First Ave, Suite HW 211, New York, NY 10016. Received April 12, 2004; revision requested June 22; revision received July 8; accepted July 28. Address correspondence to M.M. (e-mail: michael.macari@med.nyu.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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MATERIALS AND METHODS: Neither institutional review board approval nor patient informed consent was required. Between December 1999 and December 2000, 83 patients (73 men and 10 women; mean age, 61 years; range, 55–75 years) underwent endovascular repair of an infrarenal abdominal aortic aneurysm with an endoluminal stent graft. Postprocedural abdominal CT angiography was performed every 3–12 months for the evaluation of endoleaks and the maximal sac diameter. A retrospective analysis of all postprocedural CT angiographic reports was performed until November 2003 to document the presence and development of type II endoleaks and the maximal orthogonal aneurysmal sac size. Findings at CT angiography were evaluated with regard to clinical outcomes and treatment in all patients in whom type II endoleaks were observed. The postprocedural follow-up period was 1.5–4.5 years (mean, 2.5 years).
RESULTS: Twenty type II endoleaks were identified in 16 (19%) of the 83 patients. Four (20%) of the 20 endoleaks were embolized secondary to an increasing aneurysmal sac size when compared with that at preoperative CT angiography. These four leaks occurred in two patients, each with two separate endoleaks. Sixteen (80%) of the 20 endoleaks in 14 patients were managed with continued observation. In these patients, the aneurysmal sac size was stable or had decreased when compared with the size at preoperative CT angiography. Ten (62.5%) of the 16 endoleaks have sealed spontaneously during the follow-up, and six (37.5%) have persisted with stable or decreased aneurysmal sac size. None of the patients experienced aneurysmal sac rupture.
CONCLUSION: Type II endoleaks with a stable or decreased aneurysmal sac size can be followed up with CT angiography secondary to the high rate of spontaneous resolution and a low risk of rupture.
© RSNA, 2005
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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An alternative treatment option for the repair of abdominal aortic aneurysm is endovascular stent placement. Successful percutaneous transfemoral stent placement was reported in 1991 (3). When compared with open surgical repair, endovascular stent placement has been shown to decrease the incidence of systemic complications, the 30-day mortality rate, and intensive care unit and hospitalization times (4). However, there are several unique complications that may occur after stent graft placement (5,6). Complications include graft thrombosis (3%–19%), kinking and migration (18%), peripheral embolization leading to organ or limb ischemia (4%–7%), or aortic dissection (2%) (6).
The most commonly identified complication that occurs after endovascular grafting is persistent arterial flow within the aneurysmal sac (endoleak), with a reported incidence of 3%–44% (5). Five distinct types of endoleaks have been reported, including flow around the proximal or distal attachment sites (type I), retrograde flow into the aneurysmal sac from patent side branches (type II), graft malfunction or disruption (type III), graft porosity (type IV), and endotension (type V), in which the aneurysmal sac increases in size without a definite visualization of a leak on imaging studies (7).
Type II endoleak is the most commonly identified endoleak. There is controversy regarding the optimal management of this type of leak (5,7). Occlusion of all type II endoleaks has been advocated since the pressure within the sac may measure systemic levels and therefore promote sac rupture (5). Others (7) have recommended that in the absence of an expanding aneurysmal sac, observation is sufficient since many small type II endoleaks will seal spontaneously. At our institution, the majority of type II endoleaks are observed as long as the aneurysmal sac size is stable or decreased. The purpose of this study was to retrospectively determine the natural history of type II endoleaks detected at thin-section multi–detector row computed tomographic (CT) angiography.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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CT Technique
All patients underwent CT angiography both before and after stent placement. CT angiographic examinations were performed by using a multi–detector row scanner (Volume Zoom; Siemens, Forcheim, Germany) with a 0.5-second rotation speed, 120 kVp, effective mAs of 180–200, 4 x 1 or 4 x 2.5-mm detector configuration (four detectors with 1- or 2.5-mm section thickness), and beam pitch of 1.5–1.8 to image the vasculature from the celiac axis to the common femoral arteries in a 30-second breath hold. Nonionic intravenous contrast material containing 300 mg of iodine per milliliter (150 mL of iopromide, Ultravist; Berlex Laboratories, Wayne, NJ) was injected into an antecubital vein at a rate of 4 mL/sec, and data acquisition was initiated at 25 seconds or, in patients with a history of cardiac disease, by using automatic bolus tracking or a timing run. A 4 x 1-mm detector configuration was used for arteriographic phase data, and a 4 x 2.5-mm detector configuration was used for nonenhanced and venous phase data.
CT Angiography before Stent Placement
Prior to stent placement, CT angiography was performed to assess endograft inclusion criteria. The criteria included a proximal aneurysmal neck length of 15 mm or greater, a proximal neck diameter of 26 mm or smaller, a distal cuff length greater than 10 mm, an iliac artery diameter of 13 mm or smaller, and an external iliac artery diameter greater than 7 mm. In addition, the presence of mesenteric occlusive disease, a severe aortic tortuosity or calcification, and an irregular mural thrombus at the expected attachment sites were documented (8). CT angiography was performed during the arteriographic phase only. All CT angiographic examinations were networked to a workstation (Vitrea; Vital Images, Plymouth, Minn), and 1.25-mm-thick images were reconstructed at 1-mm intervals.
CT Angiography after Stent Placement
The initial postprocedure CT angiography was performed 1 month after stent placement and every 3–12 months thereafter at the discretion of the referring vascular surgeon. The CT angiography consisted of a three-phase technique that included nonenhanced, arterial phase, and an 80-second delayed acquisition. All three phases were used to evaluate for the presence of endoleaks, the maximum true orthogonal sac diameter, and other complications such as graft thrombosis and migration.
Measurements of the maximal orthogonal aneurysmal sac diameter were made on a workstation (Vitrea 2; Vital Images) by using either oblique multiplanar reformatted images directed to the course of the aorta or an automated center line plot that could be used to determine the true diameter of the aorta. Measurement of the aneurysmal sac diameter included the patent lumen, the thrombus, and the wall. These measurements were made by an abdominal radiologist using an electronic measuring device and were recorded to the nearest millimeter. Because the course of the aorta may be ectatic, measurement of the orthogonal sac diameter was performed since measurement of the aneurysmal sac diameter may be overestimated when transverse images are used.
In all cases where an endoleak was visualized, images of the endoleak and information regarding the true maximum orthogonal diameter of the aneurysmal sac were saved to an internal server for future comparison.
Data Analysis
A retrospective analysis of the dictated imaging reports from December 1999 to November 2003 was performed by a 3rd-year radiology resident (A.J.T.) using a radiology information systems database. In all patients, the reports were analyzed for the presence of type II endoleaks and referral for angiography and embolization, and the true maximal orthogonal sac size both before and after stent placement was assessed. An abdominal radiologist (M.M.) with 6 years of experience in CT angiography then confirmed the presence of all reported type II endoleaks and aneurysmal sac diameters by reviewing the saved images on the internal server. In all patients, the findings at CT angiography were evaluated in consensus by a radiologist (A.J.T.) and a nurse coordinator (R.L.) from the vascular surgery department with regard to the clinical management (follow-up angiography and embolization or observation).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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Angiography and Embolization
Two of the 16 patients with four type II endoleaks showed an increase in aneurysmal sac diameter during the follow-up period and were referred for subsequent angiography and embolization. In these two patients, the increase in aneurysmal sac diameter, when compared with that at prior CT angiography, was 3.0 mm for one patient and 4.0 mm for the other patient. Three of these four endoleaks were successfully embolized. In one case, the back-bleeding vessel could not be accessed. Findings of follow-up CT angiographic examinations in both patients during the following 36 months have shown a stable or decreased aneurysmal sac diameter without evidence of residual leak.
CT Angiographic Observation
Fourteen of 16 patients with 16 type II endoleaks did not undergo angiography and embolization. These patients underwent serial CT angiographic observation since the aneurysmal sac diameter was either stable (not changed) or had decreased when compared with that at previous CT angiography. Ten (62.5%) of these 16 endoleaks sealed spontaneously during follow-up imaging (Figs 1, 2). Six (60%) of the 10 spontaneously sealed endoleaks were primary endoleaks diagnosed at the initial 1-month postprocedure CT angiography, and four (40%) were secondary endoleaks diagnosed 3–36 months after the procedure. In all cases in which the leak had spontaneously sealed, lack of endoleak was noted at the first or second follow-up CT angiography (3–12 months).
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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At CT angiography, type II endoleaks appear as focal blushes of contrast during the arteriographic or venous phase of enhancement. By using thin-section multi–detector row CT, the back-bleeding vessel can usually be traced to a patent lumbar artery or inferior mesenteric artery. In our experience, the exiting (runoff) vessel can occasionally be directly visualized with thin-section CT angiography. Leaks that occur along the ventral aspect of the aneurysmal sac are usually caused by retrograde flow from a patent inferior mesenteric artery, while those that occur along the dorsal aspect of the sac are usually caused by a patent lumbar artery (10).
Type II endoleaks are the most common leaks, occurring in up to 24% of patients (5). A risk factor that predisposes one to type II endoleak formation is the number of patent side branch vessels, including lumbar arteries and the inferior mesenteric artery (11). The greater the number of patent side branches the greater the likelihood of leak formation. However, preprocedural embolization of patent lumbar or inferior mesenteric arteries is not performed routinely (11,12).
When a type II endoleak is identified at CT angiography, there are two management options: observation or embolization. It has been shown with use of microcatheters that the pressure within the sac related to a type II endoleak is at or near peak systole. As a result, early embolization of all type II endoleaks detected during CT angiography has been advocated (5,6,13,14). However, there is potential morbidity associated with this procedure, including groin hematoma, infection, and vascular dissection. Embolization can be a time-consuming process and is often unsuccessful secondary to difficulty in accessing the back-bleeding vessels. Many of the back-bleeding vessels are only accessible with a translumbar approach, which is associated with more substantial complications related to the development of infection and retroperitoneal hematoma (13).
Enlargement of the aneurysmal sac size (>5 mm) after endovascular repair is considered the best indicator of endotension (15). As a result, at our institution, type II endoleaks are conservatively managed (with serial follow-up imaging) as long as they are associated with a stable or decreased aneurysmal sac size. However, there are no data in the literature regarding the natural history of untreated type II endoleaks. Of the 16 leaks that were identified in patients with stable or smaller aneurysmal sacs, 10 (62.5%) have sealed spontaneously and have remained associated with a stable aneurysmal sac size. This is similar to the previously reported spontaneous resolution rate of 13%–100% (15). The six persistent type II endoleaks in our series continue to be observed and have shown a stable or decreasing aneurysmal sac size. No patient in our study with a type II endoleak experienced aneurysmal rupture.
There were several limitations to our study. Our study was retrospective, since we evaluated the dictated imaging reports to identify patients with type II endoleaks. While all abdominal radiologists interpreting these cases had experience in CT angiographic examinations performed after stent placement, it is possible that a small type II endoleak may have been missed since not all CT data were retrospectively reviewed.
A second limitation was that the size and volume of the endoleak were not calculated. It is possible that larger endoleaks may be more clinically relevant than smaller endoleaks. A follow-up study to determine the effect of the endoleak size and volume on clinical outcome may be useful in further triaging patients.
A third limitation was that we used the maximal orthogonal sac size as opposed to sac volume to follow the aneurysm. Maximal orthogonal sac size was measured by using either curved or oblique multiplanar reformatted projections, which more truly reflect the actual sac size when compared with that on transverse images, particularly when the aneurysm is tortuous. However, it is possible that an aneurysm may increase in size, which is not initially detectable at the orthogonal sac measurement. Unfortunately, most commercially available software does not allow for aneurysmal sac volume calculations.
A final limitation involves the duration of the follow-up period. While our mean follow-up period was 2.5 years, the long-term outcome in patients undergoing stent graft placement is still uncertain and should continue to be evaluated.
In conclusion, type II endoleaks occurred in 19% of patients undergoing stent graft placement for repair of abdominal aortic aneurysm. Most type II endoleaks can be managed conservatively if the aneurysmal sac diameter is stable or has decreased.
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FOOTNOTES |
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Author contributions: Guarantor of integrity of entire study, M.M.; study concepts and design, M.M., A.J.T.; literature research, M.M., A.J.T.; clinical studies, M.M., R.L., R.R., P.L.; data acquisition, R.R., M.M., R.L., P.L.; data analysis/interpretation, M.M., R.L., A.J.T.; manuscript preparation, definition of intellectual content, and revision/review, M.M., A.J.T.; manuscript editing, M.M.; manuscript final version approval, all authors
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODS RESULTS DISCUSSIONREFERENCES |
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