Aneurysm Rupture Following Limb Disconnection of a Zenith Stent Graft

Abstract

We report the case of a ruptured abdominal aortic aneurysm (AAA) related to a Type III endoleak which occurred 3 years after treatment of the AAA with a Zenith Cook stent graft. This report will also discuss the mechanism of occurrence and means of detection. An 81-year-old female underwent elective treatment of a 55 mm AAA using a right aorto-uni-iliac Zenith Cook stent graft. During follow-up, a Type II endoleak was detected and was responsible for a 4 mm aneurysm sac diameter increase. At 30 months, the patient experienced a secondary AAA rupture due to a large Type III endoleak which was caused by a separation of the main body of the stent graft and the right leg extension. A close reinterpretation of the anterior follow-up scans shows a progressive decrease of the overlap between the main body and the extension. Progressive shortening of the overlap between the main body of the graft and the limbs leads to limb disconnection. Enlargement of the aneurysm due to Type II endoleak may be a favoring factor in shortening the overlap. This case demonstrates the need for close scrutiny of all components of an endograft during follow-up.

VASCULAR DISEASE MANAGEMENT 2010;7(6):E142–E146

Key words: abdominal aortic aneurysm, morbidity, aneurysm repair, aortic aneurysm stent graft

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Introduction

Rupture following endovascular aneurysm repair (EVAR) is a dramatic event that occurs at a rate of about 1% per year or less.¹ Aortic rupture is mainly due to acute pressurization of the aneurysm sac secondary to stent-graft migration, graft erosion or limb disconnection.² Graft-related deteriorations were mostly observed with the first-generation stent grafts. Technological improvements included thicker fabric, better anchorage with hooks or strong radial forces and longer overlap between the main body and the limbs of the grafts. With the latest stent-graft generation, failures appear to occur less frequently. The Cook Zenith device (Cook, Inc., Bloomington, Indiana) was introduced on the European market in 2000. Our group reported placement of 217 Zenith stent-grafts with a 4-year follow-up.³ Component separations in these series were rare and never led to rupture. We report the case of limb disconnection of a Zenith stent graft, which led to acute AAA rupture despite a thorough surveillance protocol. We discuss the mechanisms of occurrence and means of detection.

Case Report

An 81-year-old female was referred to our department for the treatment of a 55 mm AAA. The patient was free of major comorbidities, however, considering her age, an endovascular option was chosen. A right aorto-uni-iliac procedure was performed due to the existence of a 90° angle from the longitudinal axis of the aneurysm to the left common iliac artery associated with 30 mm aneurysms of both common iliac arteries which was without a 15 mm fixation site above the iliac bifurcation. The right common iliac angulation was 60°. Assuming that preservation of internal iliac artery flow may be particularly important in endovascular repair since there is no opportunity to inspect the sigmoid colon or to reimplant the inferior mesenteric artery,⁴ the plan was to treat the aortic aneurysm and the bilateral common iliac aneurysms using a right aorto-uni-iliac endograft with a distal fixation site 15 mm into the right external iliac artery and an aortic occluder above the left iliac bifurcation (exclusion of the right internal iliac artery and conservative treatment of the left internal iliac artery). To reach the external iliac fixation zone, we added a 12 x 55 mm right-leg extension to the main endograft body. As recommended by Cook Zenith aorto-uni-iliac graft instructions for use, the overlap between the main body and the iliac leg extension was 1 stent length (15 mm). The early outcome of the intervention was uneventful. Follow-up consisted of a computed tomographic (CT) scan the day of the patient’s discharge, 6 months and 12 months and then yearly if no complication was detected. Images were viewed using Netvantage Windows volume show 3 software. Sagittal and coronal reconstructions were performed to assess the aorto-iliac angles. Maximum diameter was measured at the level of the third lumbar vertebra. All CT scans were reviewed for the purpose of this study. Postoperatively, no endoleak was detected and the sac diameter was 55 mm. At 6 months and 12 months, a Type II endoleak was observed whose origin was thought to be the lumbar arteries. Since the sac diameter shrunk to 52.8 mm, no further treatment was undertaken (Figure 1A). The patient returned at 24 months. A CT scan showed that the endoleak was still present and the aneurysm sac diameter increased to 56.8 mm (Figure 1B). An attempt to close the Type II endoleak by coil embolization of the lumbar artery and the right hypogastric artery by retrograde iliac catheterization was performed. Employing microcatheterization, we went between the right iliac limb extension and the native iliac artery. Only the internal iliac artery was successfully coiled. No Type I or Type III endoleaks were present at the end of the procedure (Figure 2). At 30 months, just after undergoing a control CT scan (Figure 4C), the patient experienced sudden onset of left lumbar pain. An emergent CT scan showed a large Type III endoleak due to separation of the main body of the stent graft and the right-leg extension (Figure 3A). The aneurysm diameter was 72 mm. Blood with contrast medium was present in the retroperitoneal space. An emergency procedure was undertaken under local anesthesia. The graft components were realigned and two 13 mm x 6 cm Fluency stents (Bard Peripheral Vascular, Inc., Tempe, Arizona) were deployed to fix the disconnection (no other adequate Cook graft was available in the emergency department). Final angiography showed that the AAA was excluded without any visible Type III endoleak, but with a persistent lumbar Type II endoleak (Figure 3B). Type II endoleak nidus embolization was performed using an Onyx (ev3, Inc., Plymouth, Minnesota) injection through a lumbar percutaneous puncture (Figure 3C). The patient’s post-operative course was uneventful and she was alive and well 24 months later. A post-procedural review of the CT scans and angiograms showed a missed progressive decrease of the overlap between the main body and the iliac extension in association with an increase of the angle between the main body and the leg extension (Figure 4). The graft’s opaque radio markers were no longer lined up and a slight kink was present. At the time of the follow-up, this migration was missed by the well-trained radiologist and the surgeon.

Discussion

This case highlights the following: 1) The occurrence of component separation, even with a current-generation stent graft; 2) The need for extensive analysis of CT scans during EVAR follow-up. Component separation is a rare event after Zenith stent-graft placement. Out of three recent series^3,5,6 with a total of 851 grafts and a follow-up period extending up to 5 years, 4 cases (0.042%), including the one reported here, have been reported. The main reasons for the rarity of limb disconnection are:⁷ • A large overlap segment with the Zenith (2 cm as compared to 1.5 cm with the Vanguard [Boston Scientific Corporation, Natick, Massachusetts]); • A relatively strong radial force of the stent along with adequate distal and proximal fixation;8 • A slightly larger diameter of the limb (14 mm ) as compared to the diameter of the short limb of the main body (12 mm). It has been reported that graft kinks were linked to aneurysm shrinkage, proximal downward migration or distal upward migration. In the current case, these mechanisms cannot be sustained. Overlap between the main body and the extension was also probably insufficient. The single stent overlap recommended by the manufacturer, when adding an iliac limb extension to a main body, is probably inadequate for angulated conformations. The aneurysm sac increased in diameter due to the Type II endoleak. We speculate that due to the AAA enlargement and the strong proximal and distal fixation, the weak point was the connection between the components. Although still the subject of controversy, Type II endoleaks are not considered benign. The incidence of Type II endoleaks at discharge or 30 days is 6–17%, 4.5–8% at 6 months, and 1–5% at 1 year.⁹ There is a consensus to treat Type II endoleaks when the aneurysm sac enlarges.10 We would like to highlight the point that Type II endoleaks per se may not lead to rupture, but with sac enlargement, they may dislodge the tips of the stent-grafts or lead to component disconnection. Parent et al¹¹ already postulated that circulating Type II endoleaks could lead to the development of Type I endoleaks due to the inability of the unsupported endograft limbs to stay in full contact with the arterial wall. Regarding our implantation strategy, the right internal iliac artery could have been embolized before the initial procedure. It could have prevented the Type II endoleak or at least prevented a possible destabilization of the right iliac limb caused by the secondary right internal iliac embolization procedure. The need for extensive analysis of CT scans for EVAR follow-up. CT scans typically include diameter measurement, the search for proximal migration by comparing the location of the device to the vertebral body or to the distance between the renal arteries and the upper part of the stent graft, and the presence of Type I or Type II endoleak. Recently, Zarins et al argued for the measurement of the horizontal distance between the graft and the vertebra.¹² The present case shows that a careful study of the radiopaque marker, and calculation of the angle are of paramount importance to detect migration of the components. We missed this information and the sac ultimately ruptured. Being aware of component migration would have led us to pre-emptively correct the defect and avoid rupture. The best protocol to study grafts and their relationship to each other and to fixed bony structures is a plain abdominal X-ray. Along with a duplex ultrasound, this strategy seems to be a more appropriate long-term strategy than selective CT scanning.¹³

Conclusion

This case demonstrates the need for close scrutiny of all the components of an endograft during patient follow-up. Early detection of shortening of the overlap between the main body of the graft and the limbs may help to prevent disconnection. An enlarging aneurysm due to a Type II endoleak may be a favoring factor of limb disconnection. Finally, we suggest that an overlap between components should be extended from one stent to at least one and a half stents, particularly in large and angulated AAAs.

Figure 4 Complete Legend: Posterior review of CT scans showed a missed progressive decrease of the overlap between the main body and the iliac extension. The graft opaque radio markers were no longer lined up and a slight kink was present. Increase of the angle between the longitudinal axis of the main body and the iliac extension: (A) at 12 months 180°–139.8° = 60.2°; (B) at 24 months 180°–132.4°= 67.6°, and (C) at 30 months 180°–125.5° = 74.5°.

References

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11. Parent FN, Meier GH, Godziachvili V, et al. The incidence and natural history of type I and II endoleak: A 5-year follow-up assessment with color duplex ultrasound scan. J Vasc Surg 2002;35:474–481.

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13. Manning BJ, O’Neill SM, Haider SN, et al. Duplex ultrasound in aneurysm surveillance following endovascular aneurysm repair: A comparison with computed tomography aortography. J Vasc Surg 2009;49:60–65.

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From the Department of Vascular Surgery, Henri Mondor Hospital, Créteil, France. The authors report no conflicts of interest regarding the content herein. Manuscript submitted December 13, 2009, provisional acceptance given February 3, 2010, final version accepted March 1, 2010. Address for correspondence: Rabih Houballah, MD, Department of Vascular Surgery, Henri Mondor Hospital, 51 Avenue du Maréchal De Lattre de Tassigny, 94000 Créteil, France. E-mail: docrabih@gmail.com