Endovascular stent graft repair of abdominal aortic aneurysms: Current status and future directions

Endovascular stent graft repair of abdominal aortic aneurysm (AAA) has undergone rapid developments since it was introduced in the early 1990s. Two main types of aortic stent grafts have been developed and are currently being used in clinical practice to deal with patients with complicated or unsuitable aneurysm necks, namely, suprarenal and fenestrated stent grafts. Helical computed tomography angiography has been widely recognized as the method of choice for both pre-operative planning and post-operative follow-up of endovascular repair (EVAR). In addition to 2D axial images, a number of 2D and 3D reconstructions are generated to provide additional information about imaging of the stent grafts in relation to the aortic aneurysm diameter and extent, encroachment of stent wires to the renal artery ostium and position of the fenestrated vessel stents. The purpose of this article is to provide an overview of applications of EVAR of AAA and diagnostic applications of 2D and 3D image visualizations in the assessment of treatment outcomes of EVAR. Interference of stent wires with renal blood flow from the hemodynamic point of view will also be discussed, and future directions explored.     

Multislice CT Angiography of Fenestrated Endovascular Stent Grafting for Treating Abdominal Aortic Aneurysms: a Pictorial Review of the 2D/3D Visualizations

Fenestrated endovascular repair of an abdominal aortic aneurysm has been developed to treat patients with a short or complicated aneurysm neck. Fenestration involves creating an opening in the graft fabric to accommodate the orifice of the vessel that is targeted for preservation. Fixation of the fenestration to the renal arteries and the other visceral arteries can be done by implanting bare or covered stents across the graft-artery ostia interfaces so that a portion of the stent protrudes into the aortic lumen. Accurate alignment of the targeted vessels in a longitudinal aspect is hard to achieve during stent deployment because rotation of the stent graft may take place during delivery from the sheath. Understanding the 3D relationship of the aortic branches and the fenestrated vessel stents following fenestration will aid endovascular specialists to evaluate how the stent graft is situated within the aorta after placement of fenestrations. The aim of this article is to provide the 2D and 3D imaging appearances of the fenestrated endovascular grafts that were implanted in a group of patients with abdominal aortic aneurysms, based on the multislice CT angiography. The potential applications of each visualization technique were explored and compared with the 2D axial images.     

MSCT血管成像对腹主动脉瘤的诊断价值

目的:评价多层螺旋CT血管成像(MSCTA)在诊断腹主动脉瘤中的价值.方法:对31例经手术证实的腹主动脉瘤患者的MSCTA与数字减影血管造影(DSA)进行对照性研究.采用容积再现(VR)、最大密度投影(MIP)、多平面重组(MPR)、仿真内镜技术(VE)及表面遮盖显示(SSD)后处理方法.结果:MSCTA与DSA对腹主动脉瘤的诊断符合率达100%,对瘤体长度、近端瘤颈直径、近端瘤颈长度、近端瘤颈角度等参数的测量无明显差异,对瘤体直径的测量值差异有显著性,MSCTA测量值较DSA准确.结论:MSCTA可明确诊断腹主动脉瘤,对重要参数的测量值准确,可作为腹主动脉瘤诊断及术前评估的首选影像学检查方法.     

Juxtarenal aortic aneurysm: endoluminal transfemoral repair?

Endoluminal transfermoral repair of an abdominal aortic aneurysm by a stent graft placement requires a segment of the nondilated infrarenal aorta of at least 15 mm long for safe stent graft attachment. The possibility of endoluminal treatment of a juxtarenal abdominal aortic aneurysm with partially covered spiral Z stent was assessed in experiment and in three clinical cases. In the experiment, the noncovered spiral Z stent was placed into the abdominal aorta, across the origins of renal arteries and mesenteric arteries, in six dogs. In the clinical cases, a partially covered stent graft was attached in 3 patients with the juxtarenal abdominal aortic aneurysm (of the group of 12 patients with abdominal aortic aneurysm). The stent grafts were attached with proximal uncovered parts across the origins of the renal arteries. In experiment, the renal artery occlusions or stenoses were not observed 36 months after stent placement, and in clinic 3 patients with the juxtarenal aortic aneurysm were successfully treated by stent graft placement. There were no signs of flow impairment into the renal arteries 14 months after stent graft implantation. This approach can possibly expand the indications for endoluminal grafting in the treatment of juxtarenal aortic aneurysms in patients who are at high risk for surgery.     

Fenestrated Stent Graft Repair of Abdominal Aortic Aneurysm: Hemodynamic Analysis of the Effect of Fenestrated Stents on the Renal Arteries

Objective

We wanted to investigate the hemodynamic effect of fenestrated stents on the renal arteries with using a fluid structure interaction method.

Materials and Methods

Two representative patients who each had abdominal aortic aneurysm that was treated with fenestrated stent grafts were selected for the study. 3D realistic aorta models for the main artery branches and aneurysm were generated based on the multislice CT scans from two patients with different aortic geometries. The simulated fenestrated stents were designed and modelled based on the 3D intraluminal appearance, and these were placed inside the renal artery with an intra-aortic protrusion of 5.0-7.0 mm to reflect the actual patients'' treatment. The stent wire thickness was simulated with a diameter of 0.4 mm and hemodynamic analysis was performed at different cardiac cycles.

Results

Our results showed that the effect of the fenestrated stent wires on the renal blood flow was minimal because the flow velocity was not significantly affected when compared to that calculated at pre-stent graft implantation, and this was despite the presence of recirculation patterns at the proximal part of the renal arteries. The wall pressure was found to be significantly decreased after fenestration, yet no significant change of the wall shear stress was noticed at post-fenestration, although the wall shear stress was shown to decrease slightly at the proximal aneurysm necks.

Conclusion

Our analysis demonstrates that the hemodynamic effect of fenestrated renal stents on the renal arteries is insignificant. Further studies are needed to investigate the effect of different lengths of stent protrusion with variable stent thicknesses on the renal blood flow, and this is valuable for understanding the long-term outcomes of fenestrated repair.     

国产覆膜支架介入治疗腹主动脉瘤的实验研究

 目的建立10只犬腹主动脉瘤模型,以介入法置入国产覆膜支架,观察其改变.方法10只实验动物建立模型;国产覆膜支架治疗后,CT进行影像学复查;最后取病理检查.结果两只发生并发症,余犬治疗后管腔通畅,但局部管腔有狭窄,病理电镜示覆膜支架内有内皮细胞生长.结论国产覆膜支架介入治疗腹主动脉瘤安全、有效.     

Initial experience of branched endovascular graft for abdominal aortic aneurysm with complex anatomy of proximal neck: planning and technical considerations

The purpose of this report was to demonstrate initial Japanese cases of abdominal aortic aneurysm (AAA) with complex anatomy of proximal neck treated using a Zenith fenestrated endograft with branched endovascular technique and to describe the device’s design and technical considerations. Planning and sizing of endografts were performed using high-resolution computed tomography on a three-dimensional workstation. Branched endograft technique combined with reinforced fenestrated device and balloon-expandable stent graft was used in two patients because of challenging morphology for the fenestrated device with a bare stent. Successful exclusion of the aneurysm sac was achieved in both patients with antegrade perfusion in incorporated visceral vessels. Endovascular repair using a fenestrated device with graft material incorporating the visceral arteries is feasible. The combination of the reinforced fenestration and the balloon-expandable stent graft can provide an adequate sealing effect for the compromised anatomy. Initial and midterm results are reported with further follow-up and patient accrual.     

The Renal Impact of Aortic Stent-Grafting in Patients with a Horseshoe Kidney

Aortic stent grafting may be an alternative to surgery for patients with an abdominal aortic aneurysm and coexistent horseshoe kidney but is not without difficulties. This study examines the renal consequences of aortic stent grafting in such patients. This is a retrospective review of patients with horseshoe kidney in whom aortic stent grafting was performed between December 1995 and August 2000. Follow-up occurred within the EUROSTAR protocol and included measurement of serum creatinine. Of 130 patients in whom aortic stent grafting was performed, 4 had coexistent horseshoe kidney. In all patients the aneurysm was successfully excluded with the occlusion of between one and four anomalous renal arteries. At follow-up, no clinically significant renal impairment was detected. Endovascular aneurysm repair is an attractive option for patients with a horseshoe kidney and normal preoperative creatinine levels.     

Three-year follow-up of fenestrated thoracoabdominal stent graft bridging an endovascular thoracic stent graft and a surgical abdominal aortic graft

This case report describes repair of a type I endoleak at the distal landing zone of a thoracic aortic stent graft by endovascular placement of a thoracoabdominal fenestrated stent graft (Cook, Brisbane, Australia). The fenestrated stent graft was interposed between a previous abdominal aortic aneurysm (AAA) Gelsoft tube graft (Sulzer Vascutek Ltd, Inchinnan, United Kingdom) and two overlapping Zenith thoracic endografts (Cook Inc, Bloomington, Indiana). Placement was made more complex because the distal thoracic endograft had rotated into a horizontal position. At 3-year clinical and computed tomography (CT) follow-up, continued clinical and radiologic success was shown with no further intervention required.     

多层螺旋CT血管成像在腹主动脉瘤中的诊断应用

目的探讨多层螺旋CT血管成像在腹主动脉瘤（AAA）中的诊断价值。方法30例临床疑诊AAA患者均经16层螺旋CT血管成像（MSCTA）。采用最大密度投影（M1P）、多平面重组（MPR）、容积再现（VR）技术对传送至AW4.1工作站的原始数据进行重建,获得二维或三维的立体图像。结果30例疑诊AAA患者中有7例真性腹主动脉瘤,15例假性动脉瘤,8例主动脉夹层。MPR能准确显示瘤体位置、形态、范围及附壁血栓。MIP能较好地显示瘤壁及附壁血栓内的钙化。VR技术能立体精确显示腹主动脉、瘤体及周围组织结构的空间关系。结论多层螺旋CT血管成像是一种无创、快速的检查方法,为临床诊断、治疗腹主动脉瘤提供重要信息。     

Helical CT Angiography of Abdominal Aortic Aneurysms Treated with Suprarenal Stent Grafting: A Pictorial Essay

The endovascular repair of abdominal aortic aneurysm (AAA) with stent grafts is rapidly becoming an important alternative to open repair. Suprarenal stent grafting, recently modified from conventional infrarenal stent grafting, is a technique for the purpose of treating patients with inappropriate aneurysm necks. Unlike open repair, the success of endoluminal repair cannot be ascertained by means of direct examination and thus relies on imaging results. The use of conventional angiography for arterial imaging has become less dominant, while helical computed tomography angiography (CTA) has become the imaging modality of choice for both preoperative assessment and postoperative followup after treatment with stent graft implants. There is an increasing likelihood that radiologists will become more and more involved in the procedure of aortic stent grafting and in giving the radiological report on these patients treated with stent grafts. It is necessary for radiologists to be familiar with the imaging findings, including common and uncommon appearances following aortic stent grafting. The purpose of this pictorial essay is to describe and present normal and abnormal imaging appearances following aortic stent grafting based on helical CTA.     

Assessment of VIE image quality using helical CT angiography: in vitro phantom study.

The aim of this study is to quantify the effects of helical CT acquisitions parameters on the magnitude of three-dimensional stair-step artefacts, visualization of renal ostium and morphologies of suprarenal stents observed using virtual intravascular endoscopy. This was performed in a phantom of the human abdominal aorta with a stent graft in situ. Stair-step artefacts were quantified by measuring the standard deviation of signal intensity on surface shaded images and the influence of these artefacts on the visualization of arterial ostia and stent morphologies were assessed by three radiologists. The methodology may be used to optimise the CT system performance for helical CT angiography in aortic stent grafting.     

Stent grafting of abdominal aortic aneurysms: pre-and postoperative evaluation with multislice helical CT

Endovascular stent grafting of abdominal aortic aneurysms is a new technique that may replace open surgery in selected cases. Pre-and postoperative angiography can be replaced by helical CT. This pictorial essay describes and illustrates the use of multislice helical CT where maximum intensity projection and multiplanar reformats play a central role in the evaluation.     

Abdominal aortic aneurysm. Detection of multilevel vascular pathology by time-resolved multiphase 3D gadolinium MR angiography: initial report.

OBJECTIVE: To evaluate multiphasic 3D gadolinium-enhanced magnetic resonance angiography (3D-Gd-MRA) for detection of vascular pathology at multiple levels of the aorta and iliac arteries. METHODS: In 18 patients with abdominal aortic aneurysm (n = 13), dissection (n = 3), or both (n = 2), multiphase 3D-Gd-MRA was performed acquiring five consecutive (6.8 seconds) 3D data sets in a single breath-hold. In each of the five time-resolved phases, vessel visibility of the abdominal aortic branches and iliac arteries was assessed. The extent of vessel involvement by the aneurysm or dissection seen on multiphase 3D-Gd-MRA was compared with standard imaging and surgical findings. Digital subtraction angiography was available for comparison in 4 cases, CT angiography in 10 cases. RESULTS: Due to the delayed filling of the aortic aneurysm, the proximal aortic branches and the aneurysm neck demonstrated an inversely related enhancement compared with the distal abdominal and iliac vessels (P < 0.001). Review of all five phases of multiphase 3D-Gd-MRA allowed optimal visualization of each vessel segment without any artifacts due to parenchymal or venous overlay. In dissections, review of three phases was required (P < 0.001) for diagnostic evaluation of the true and false lumens. Substantially more vessel involvement was detected on multiphase 3D-Gd-MRA; this was surgically confirmed in 10 of 11 cases and affected therapy management in 11 of 18 cases. CONCLUSIONS: Multiphase 3D-Gd-MRA is a convenient, robust, and safe technique for presurgical anatomic mapping of complex aortic aneurysms and dissections.     

内支架置入术治疗胸腹主动脉瘤的临床评价

目的：探讨胸腹主动脉瘤的ESG治疗临床疗效。方法：对10例患者分别行CTA、MRA、DSA检查和ESG治疗，其中Stanford B型夹层动脉瘤6例，真性腹主动脉瘤2例，肾动脉开口以下腹主动脉瘤2例（行分体式支架），所有病例均采用带膜支架。结果：8例行一体式支架腔内隔绝术，2例行分体式支架腔内隔绝术，均获成功。顺利植入，术后造影提示动脉瘤消失．无内漏发生。患者症状完全消失，全部患者在随访期间均未出现术前症状，未见相关并发症。结论：应用ESG治疗胸腹主动脉瘤安全、有效、创伤小、术后恢复快，长期疗效尚待进一步观察。     

主动脉瘤多层螺旋CT血管成像的临床应用价值

目的探讨多层螺旋CT血管成像(MSCTA)技术在诊断主动脉瘤中的临床应用价值.资料与方法对32例主动脉瘤和主动脉夹层患者进行MSCTA检查,将原始图像传至工作站进行后处理,运用不同的重建方法对血管进行显示,包括多平面重组(MPR)、最大密度投影(MIP)、表面遮盖法(SSD)和容积再现(VR)技术.结果主动脉瘤13例,主动脉夹层19例,多种重建图像与轴位图像相结合能清晰地显示动脉瘤的解剖细节及其与周围器官的空间解剖关系.结论 MSCTA技术对主动脉瘤的诊断具有独特的优越性,对于选择治疗方法、观察术后疗效及随访具有重要价值.     

Renal artery aneurysm: diagnosis and surveillance with multidetector-row computed tomography

Purpose: To investigate the prevalence of renal artery aneurysms, and to assess the value of multidetector-row computed tomography (MDCT) in diagnosing renal artery aneurysms.

Material and Methods: Altogether, 862 patients underwent arterial-phase contrast-enhanced CT scan of the abdomen in the period November 2003 to October 2005. A search for renal artery aneurysms was performed in our reporting system and revealed six patients with renal artery aneurysm (RAA).

Results: The incidence of RAA was 0.7%. All renal artery aneurysms were solitary, located in the main trunk or the first branch of the renal artery, with sizes from 1.5 cm to 3.4 cm. Five aneurysms were saccular, one fusiform. No underlying thrombosis was seen. Extensive calcification was found in one aneurysm. Three aneurysms were diagnosed using axial images, while three aneurysms were only displayed by volume rendering and maximum-intensity projection images.

Conclusion: This study demonstrates a 0.7% incidence of renal artery aneurysms in a total of 862 patients. MDCT has an important role in detecting and assessing renal artery aneurysms. Some aneurysms can only be displayed by post-processing techniques such as volume rendering and maximum-intensity projection.     

多层螺旋CT血管造影在主动脉夹层及主动脉瘤诊断中的价值

目的：探讨多层螺旋CT血管造影在主动脉夹层及主动脉瘤中的临床应用价值。方法：对34例临床怀疑主动脉疾病者进行CT血管造影，层厚3．2mm，重建间隔1．6mm，pitchl 25，对比剂用量100ml，注射速度3ml/s，延迟时间23～28s；对所有病人进行最大密度投影、多平面重组、表面遮盖显示、仿真内窥镜、容积再现重组。结果：34例中，正常者7例，主动脉夹层16例，主动脉瘤7例，左锁骨下动脉瘤1例，马凡综合征1例，主动脉弓血管置换术后1例，腹主动脉瘤血管内支架术后1例。结论：MSCTA在主动脉夹层及主动脉瘤中有积极的临床应用价值，横断面CTA为诊断主动脉疾病的基础，图像后处理技术作为补充。     

CT断层图像和三维重建在主动脉腔内隔绝术术前评估中的价值

目的比较CT断层图像和三维重建在主动脉腔内隔绝术术前评估中的价值。方法将接受主动脉腔内隔绝术的20例主动脉夹层瘤和12例腹主动脉瘤患者作为研究对象,术前分别在CT断层图像与三维重建图像上测量的各相关参数,与主动脉造影所测量的相同参数进行对照分析。结果CT断层图像上所测量的主动脉弓直径及各种长度指标均小于主动脉造影结果;夹层瘤近段主动脉直径及近端瘤颈直径、主动脉中段直径以及左右髂动脉直径均大于主动脉造影结果;三维重建所测量的上述各项参数与主动脉造影结果非常接近,并能清楚显示夹层分离的破裂口,而断层图像上不易发现破裂口;断层图像和三维重建在显示主动脉附壁血栓和测量最大瘤体直径方面优于主动脉造影。以三维重建测量为标准选择覆膜支架,所有患者均成功封闭瘤体。结论主动脉腔内隔绝术术前评估时应结合CT断层图像和三维重建图像综合分析,覆膜支架的选择应以三维重建测量结果为主。     

Tuberculous Aneurysm of the Abdominal Aorta: Endovascular Repair Using Stent Grafts in Two Cases

Tuberculous aneurysm of the aorta is exceedingly rare. To date, the standard therapy for mycotic aneurysm of the abdominal aorta has been surgery involving in-situ graft placement or extra-anatomic bypass surgery followed by effective anti-tuberculous medication. Only recently has the use of a stent graft in the treatment of tuberculous aortic aneurysm been described in the literature. We report two cases in which a tuberculous aneurysm of the abdominal aorta was successfully repaired using endovascular stent grafts. One case involved is a 42-year-old woman with a large suprarenal abdominal aortic aneurysm and a right psoas abscess, and the other, a 41-year-old man in whom an abdominal aortic aneurysm ruptured during surgical drainage of a psoas abscess.