- Email: [email protected]
MDCT of endoleaks following endovascular repair of abdominal aortic aneurysms
Clinical Imaging 39 (2015) 367–373
Contents lists available at ScienceDirect
Clinical Imaging journal homepage: http://www.clinicalimaging.org
MDCT of endoleaks following endovascular repair of abdominal aortic aneurysms Matthew T. Heller a, Amar B. Shah b, Puneet Bhargava c, Udayan Srivastava a,⁎, Xiameng Sun a a b c
Department of Radiology, University of Pittsburgh School of Medicine, 200 Lothrop St, Suite 3950 PUH S. Tower, Pittsburgh, PA 15213 Westchester Medical Center, Department of Radiology, 100 Woods Road Room 1319, Macy Pavilion, Valhalla, NY 10595 Mail Box 358280, S-114/Radiology, VA Puget Sound Health Care System, 1660 S Columbian Way, Seattle, WA 98108
a r t i c l e
i n f o
Article history: Received 21 June 2014 Received in revised form 11 November 2014 Accepted 5 January 2015 Keywords: EVAR AAA MDCT Aneurysm Endoleak
a b s t r a c t Endovascular aneurysm repair has been used to repair abdominal aortic aneurysms but necessitates surveillance to diagnose the delayed possibility of endoleak formation. Multi-detector computer tomography (MDCT) of the abdomen is one imaging technique used to diagnose enlargement of the aneurysm sac that may be indicative of endoleaks. MDCT has a role in identifying the initial endoleak formation and providing signs suggestive of the specific endoleak subtype; thus it is necessary for radiologists to be familiar with the findings of endoleak seen on MDCT. In this pictorial review, we explore the various types of endoleaks and their appearance on MDCT. © 2015 Elsevier Inc. All rights reserved.
1. Introduction Aneurysms of the abdominal aorta (AAA) are frequently observed incidentally during multi-detector computed tomography (MDCT) of the abdomen. AAA may also present as an aorto-enteric fistula [1,2]. The incidence of abdominal aortic aneurysm increases with age; AAA is estimated to occur in up to 12.5% of men and 6% of women aged 75–84 years [3]. Annually, in the United States, over 40,000 patients undergo repair of aneurysms of the abdominal aorta [4]. AAA repair remains one of the highest risk surgical procedures, second only to colectomy for the highest number of annual perioperative deaths [5]. Historically, open surgical repair was the mainstay of treatment for aneurysms of the abdominal aorta. Although successful, the associated perioperative morbidity and often lengthy recovery time are drawbacks of the open repair [6]. Endovascular aneurysm repair (EVAR) was introduced in the early 1990s and was touted as a less invasive alternative to the traditional open aneurysm repair [7]. Over the past two decades, refinement of the EVAR technique has produced an initial survival advantage and yielded a similar long-term survival to open repair [8]. Despite these advantages, however, delayed rupture remains a concern for patients undergoing EVAR. The complication of delayed rupture is preceded by progressive aneurysm expansion that may develop despite uneventful technical
⁎ Corresponding author. University of Pittsburgh School of Medicine, Department of Radiology, 200 Lothrop St, Suite 3950 PUH S. Tower, Pittsburgh PA 15213. Tel.: +1 412 647 3550; fax: +1 412 647 7795. E-mail address: [email protected] (U. Srivastava). http://dx.doi.org/10.1016/j.clinimag.2015.01.004 0899-7071/© 2015 Elsevier Inc. All rights reserved.
performance of EVAR [9,10]. Progressive aneurysm expansion is multifactorial, but a significant contributing factor is the development of an endoleak. An endoleak is defined as blood flow external to the stentgraft but inside the aneurysm sac [11]. Certain types of endoleaks, most commonly type II endoleaks, allow the aneurysm sac to communicate with systemic circulation. When the aneurysm sac is continually exposed to the high pressures of systemic circulation, the aneurysm sac can progressively enlarge. If endoleaks are not diagnosed early, the progressive enlargement of the aneurysm sac can lead to catastrophic rupture. Therefore, patients who have undergone EVAR require imaging surveillance of the stent graft throughout their lifetime. While various imaging modalities can assess the temporal changes of the size of the aneurysm sac, MDCT is an effective and specific technique that is commonly employed [12]. Since diagnosis of endoleaks can be challenging, it is imperative for the radiologist to be familiar with the MDCT findings and their significance with respect to ramifications for treatment [13,14]. This pictorial review will illustrate and discuss the key MDCT findings of the types of endoleaks following EVAR and briefly discuss their general management.
2. MDCT technique and normal post-operative appearance MDCT angiography has evolved into a reliable imaging modality for the evaluation of patients who have undergone EVAR. MDCT is rapidly performed and has a higher sensitivity for detecting endoleaks compared with conventional catheter angiography [15]. Multi-detector technology has evolved to enable imagers to acquire thin section datasets with high spatial resolution over short acquisition periods, reducing patient motion
368
M.T. Heller et al. / Clinical Imaging 39 (2015) 367–373
artifact [16]. The decreased scan time afforded by MDCT has also allowed manipulation of the administration of intravenous contrast material using smaller volumes of contrast. In addition, advances in contrast injector design allow imager to use higher contrast flow rates allowing for better opacification of the stent graft [17,18]. Additionally, the use of bolus tracking software has contributed to improved reliability and reproducibility of MDCT. While MDCT protocols for evaluating the patient after EVAR will vary according to scanner type and institution, protocols generally consist of two or three phases of imaging [19,20]. The general components of a typical protocol may consist of non-contrast imaging and post-contrast imaging during the arterial and/or delayed venous phases [21]. However, some investigators have shown that diagnostic performance can be maintained without employing all of these phases. While the arterial phase was initially thought to aid in the detection and treatment planning of endoleaks, another study did not find the acquisition of arterial phase images to be mandatory [22]. Pre-contrast images may be considered useful in distinguishing endoleaks from focal calcification in the aneurysm sac, while the delayed venous phase can detect endoleaks with slower flow that are not apparent during the arterial phase [19,21]. However, since radiation dose increases with a higher number of phases, some centers have chosen to eliminate the non-contrast images and perform only postcontrast biphasic imaging; calcifications can still be discriminated from a leak since the hyperattenuation from iodine will decrease from the arterial to the delayed phases while the attenuation of calcium will remain constant between the two phases. Additionally, the use of dual energy CT has allowed reconstruction of virtual non-contrast images to substitute for actual image acquisition of the traditional non-contrast phase [23,24]. It has also been demonstrated that reconstruction of virtual non-contrast images and additional post-processing techniques from a single phase, dual-energy protocol significantly lowers radiation dose while maintaining extremely high diagnostic accuracy [25]. As with open repair, the goal of EVAR is to isolate flow in the aortic lumen from the aneurysm sac, to prevent further aneurysm enlargement and rupture. The EVAR procedure consists of percutaneous insertion of the collapsed stent-graft via the femoral artery, positioning with use of digital subtraction angiographic images, and deployment of the stent-graft within the aortic lumen to cover the length of the aneurysm. Stent-grafts can be made from a number of materials, including a combination of steel, nitinol or elgiloy, and a cover of plastic or polyester. On MDCT, the walls of the stent-grafts are thin (b2 mm) and hyperattenuating. Imaging artifacts from stentgrafts are generated less common with MDCT compared with magnetic resonance imaging (MRI); however, on occasion, mild streak artifact may be encountered with nitinol and elgiloy compositions [26]. The stent-graft is anchored proximally to the non-aneurysmal aspect of the abdominal aorta and distally within the common iliac arteries (Fig. 1). The proximal aspect of the stent graft consists of a single, central lumen that is opacified during contrast-enhanced MDCT. The surrounding excluded aneurysm sac consists of low attenuation thrombus; On occasion, areas of higher attenuation will be visualized and are thought to be due to dystrophic calcification of the mural thrombus, but no areas of contrast enhancement should be present normally. In the infrarenal aorta, distal to the proximal anchors of the endovascular stent graft, a ‘double lumen’ is observed due to the presence of the bifurcating limbs of the stent-graft proximal to their course within the common iliac arteries. Once the limbs enter their respective common iliac arteries, a single lumen is again observed. The proximal and distal anchors of the stentgraft make a sharp interface with the vessel lumen; a slight lumen caliber difference is often observed at the level of the anchors due to the differential size of the vessel lumen containing the stent versus the native lumen. The diameters of the excluded aneurysm sac should decrease after EVAR. During the initial post-operative MDCT, the size reduction may not be impressive depending on time elapsed since surgery; however, the diameters should tread downward over subsequent surveillance MDCT examinations. The proximal and distal anchors of the stent graft should also remain intact and be in identical anatomic positions on subsequent imaging.
3. Role of MDCT in endoleak diagnosis Estimating the precise incidence of endoleaks is difficult to determine since this information has largely been derived from single institutional studies which used various imaging technology and technique [27]. However, it is accepted that the majority of endoleaks are type II, followed by type I, and then type III. Although the cause, location and size of endoleaks can vary, the general appearance of an endoleak is similar regardless of type. An endovascular stent graft leak on MDCT shows contrast material outside of the confines of the stent-graft and within the excluded aneurysm sac. Despite MDCT's value in detecting endoleaks, it is less specific than conventional digital subtraction angiography for characterization of the type of leak [28]. The lower specificity of MDCT angiography stems from its relative inability to determine direction of blood flow, a critical component of endoleak characterization [21]. Endoleaks detected with MDCT often benefit from undergoing digital subtraction angiography to assure proper characterization since reclassification can change treatment [28]. Post-contrast MRI has also been shown to be superior for the detection of endoleaks compared with MDCT [29]. While digital subtraction angiography remains the reference standard for the characterization of endoleaks due to its higher temporal resolution and ability to determine direction of flow, it is important that the radiologist is familiar with the key MDCT findings of the different types of endoleaks and their general management (Table 1). 4. Types of endoleaks 4.1. Type I endoleaks Type I endoleaks originate at the stent-graft attachment sites due to an incomplete seal between the stent-graft and the arterial wall. This results in communication between the systemic circulation and the excluded aneurysm sac. Type I endoleaks can be classified as proximal (Type Ia) or distal (Type Ib) [13]. A third subclasification (Type Ic) denotes the rare instance when there is retrograde filling of an aneurysm in a patient who underwent simultaneous EVAR and femoral-femoral bypass with occlusion of the contralateral femoral artery; retrograde flow into the aneurysm sac occurs because of incomplete occlusion of the femoral artery. Types Ia and Ib endoleaks are most common in patients with atypical arterial anatomy (tortuosity, peripheral thrombus) and after EVAR of a thoracic aortic aneurysm [30]. An MDCT finding that is suggestive of a type I endoleak is the presence of abnormal enhancement that abuts or communicates with the proximal or distal attachment sites (Fig. 2). If the endoleak is sufficiently large, the leaked blood may dissect away from the anchors and into the central aspect of the excluded aneurysm sac. In these cases, it may be especially difficult to differentiate a type I endoleak from type II and III endoleaks on MDCT, requiring digital subtraction angiography for clarification. Large type I leaks resulting in build-up of high pressure between the aortic wall and the stent-graft can result in a mural tear of the aorta at the level of the attachment site. 4.2. Type II endoleaks Type II endoleaks are the most common type of endoleak and are due to retrograde flow of blood into the aneurysm sac. Retrograde blood flow most commonly occurs through various aortic branch vessels such as the lumbar arteries and inferior mesenteric artery. Retrograde flow through these vessels re-establishes communication between the excluded aneurysm sac and systemic circulation. During MDCT angiography, a Type II endoleak typically appears as enhancement in the peripheral aspect of the aneurysm sac (Fig. 3) [31]. If the abnormal enhancement is located in the anterior aspect of the excluded aneurysm sac, the supply may be from the inferior mesenteric artery while a posterior location implies supply from a lumbar artery. The presence of contrast within the inferior mesenteric or lumbar arteries is not
M.T. Heller et al. / Clinical Imaging 39 (2015) 367–373
369
Fig. 1. Abdominal aortic aneurysm before and after EVAR. (A) Volume rendered 3-dimensional reconstructed image in a patient with a fusiform AAA (arrow). (B) After EVAR, the volume rendered image shows the bifurcating stent-graft (arrow) and the borders of the excluded aneurysm sac (arrowheads). (C) Axial enhanced MDCT during the late arterial phase shows the AAA prior to repair. (D) Following EVAR, the axial enhanced MDCT during the arterial phase shows flow in the lumen of the stent-graft (arrow) and no flow within the excluded aneurysm sac (arrowheads). (E) More inferiorly, an axial enhanced MDCT image during the late arterial phase shows the largest transverse section of the AAA (arrowheads) prior to repair. (F) Following EVAR, the axial enhanced MDCT during the arterial phase demonstrates that contrast opacifies two lumens (arrows) due to the bifurcating limbs of the stent graft. There is no flow in the excluded aneurysm sac (arrowheads). (G) Axial enhanced MDCT during the late arterial phase shows the heavily calcified right common iliac artery (arrow) and tapering of the AAA prior to repair. (H) Following EVAR, the axial enhanced MDCT during the arterial phase demonstrates that the distal anchors of the stent-graft extend into the right common iliac artery (arrow). There is absence of flow in the excluded aneurysm sac (arrowhead).
Table 1 Endoleak classification and summary Endoleak classification summary
Location Etiology Key MDCT finding
Significance Treatment
Type 1
Type 2
Type 3
Type 4
Type 5
Proximal (1a) or distal (1b) anchors Incomplete seal between graft and vessel wall Contrast in excluded aneurysm sac which is continuous with attachment sites
Insertion of aortic branch vessels
Variable, but typically occur centrally Component separation or tear of graft material Contrast in central aspect of excluded aneurysm sac away from attachment sites and branch vessel insertions High pressure endoleak → high risk of rupture Urgent angiographic evaluation/intervention
Diffuse
Unknown
Porosity of graft material
Potential occult defect in graft Continued enlargement of excluded aneurysm sac without radiographic identification of a leak
High pressure endoleak → high risk of rupture Urgent angiographic evaluation/intervention
Retrograde flow via aortic branch vessels. Contrast in excluded aneurysm sac located peripherally at site of branch artery insertion (i.e.-lumbar or inferior mesenteric arteries) Less pressure than Types 1 or 3—may close spontaneously; Treatment if increasing size of aneurysm sac or symptoms
Transiently observed during endovascular procedure; no MDCT findings Resolve after cessation of anticoagulation None
Low risk in short-term Angiography to evaluate for occult leak; surgery if enlarging
370
M.T. Heller et al. / Clinical Imaging 39 (2015) 367–373
Fig. 2. Type I endoleak. Axial enhanced MDCT during the arterial phase in a patient presenting with left flank pain and hypotension. (A) The image demonstrates abnormal flow (arrow) posterior to the superior margin of the proximal anchors of the stent-graft. There is extensive hematoma (arrowheads) in the left aspect of the retroperitoneum. (B) More inferiorly, the axial enhanced MDCT image reveals that the abnormal flow (arrow) enters the excluded aneurysm sac. The retroperitoneal hematoma (arrowheads) is due to rupture of the excluded aneurysm sac. (C) Volume rendered 3-dimensional image demonstrates the site of endoleak (arrow) at the level of the proximal anchors and extension of leaked blood (arrowhead) into the excluded aneurysm sac. (D) Surgical specimen shows a defect in the stent-graft near the proximal anchors.
specific for a Type II endoleak. Contrast in these vessels can theoretically be due to inflow from retrograde flow, a Type II endoleak, or outflow from Type I or III endoleaks. Although peripheral location of abnormal enhancement within the excluded aneurysm sac during MDCT is suggestive of a Type II leak, definitive characterization with digital subtraction angiography would be needed to establish the direction of flow [21]. The size of a suspected type II endoleak should be accurately reported
since those larger than 15 mm have been associated with aneurysm expansion [32]. 4.3. Type III endoleaks Type III endoleaks are relatively uncommon and result from mechanical failure of the graft material. Failure can occur in the form of
Fig. 3. Type II endoleak. Axial enhanced MDCT during the arterial phase in a patient presenting for routine surveillance following EVAR. (A) The image shows enhancement within the posterior aspect of the excluded aneurysm sac (arrow) due to retrograde flow from a lumbar artery (arrowhead). (B) More inferiorly, leaked contrast (arrow) accumulates in the posterior aspect of the excluded aneurysm sac.
M.T. Heller et al. / Clinical Imaging 39 (2015) 367–373
371
fracture, junctional separations, or focal defects from corrosion or tear of the stent-graft fabric. Potential etiologies for stent-graft failure include repetitive mechanical stresses from arterial pulsations, movement and shrinkage of the excluded aneurysm sac. An MDCT finding associated with type III endoleaks is abnormal enhancement surrounding the stent-graft with sparing of the periphery of the excluded aneurysm sac [33]. If this finding is present, the stent-graft should be carefully evaluated for a focal defect. Additionally, the presence of focal enhancement adjacent to a junction point should raise concern for a type III endoleak (Fig. 4).
phenomenon is referred to as endotension; potential etiologies include the presence of a co-existing occult endoleak (Type I, II or III), filtration of blood through the stent-graft fabric or an ineffective barrier to pressure transmission [34,35]. The MDCT finding is progressive expansion of the excluded aneurysm sac (Fig. 5). In such cases, further evaluation with other imaging modalities (magnetic resonance angiography, ultrasound, or angiography) is recommended to thoroughly exclude an endoleak that is occult on MDCT.
4.4. Type IV endoleaks
No consensus criteria have been established for the frequency of surveillance imaging for patients who have undergone EVAR. While various guidelines have been proposed, institutional variability persists [36]. Most recommendations for patients who have undergone EVAR employ surveillance MDCT and radiography at regular intervals; the frequency of surveillance increases for patients with types II and V endoleaks, while types I and III generally undergo treatment at the time of diagnosis [37]. Additionally, since endoleaks have been reported to occur as long as 7 years after EVAR, there are no established criteria for reduction of frequency of surveillance imaging for patients who remain without an endoleak years after surgery [27]. Treatment of endoleaks is determined by the type of endoleak present. Types I and III endoleaks are treated immediately after diagnosis since these types constitute a direct communication between the
Type IV endoleaks are due to the porosity of the stent-graft material and have no MDCT findings. Type IV endoleaks are observed as a transient blush of contrast within the excluded aneurysm sac. This phenomenon is observed in the angiography suite immediately following placement of the stent-graft while the patient is anticoagulated. Since type IV endoleaks are self-limited, no treatment or additional followup is required beyond the usual surveillance imaging. 4.5. Type V endoleaks Type V endoleaks are defined as expansion of the excluded aneurysm sac without identification of another type of endoleak. This
5. Follow-up imaging and treatment
Fig. 4. Type III endoleak. Axial enhanced MDCT during the arterial phase in a patient presenting for routine surveillance following EVAR. (A) The image shows a large collection of leaked contrast (arrow) within the excluded aneurysm sac. Coronal (B) and sagittal (C) enhanced MDCT during the arterial phase demonstrate that the endoleak (arrow) originates from the left iliac junction point (arrowhead) of the stent-graft. (D) Digital subtraction angiogram shows a catheter in the left iliac artery and a contained leak at the junction of the left limb.
372
M.T. Heller et al. / Clinical Imaging 39 (2015) 367–373
Fig. 5. Type V endoleak. Volume rendered 3-dimensional MDCT reconstruction in a patient presenting for routine surveillance following EVAR. (A) The image shows a relatively small caliber of the excluded aneurysm sac (arrowheads). (B) Six months later, there has been substantial enlargement of the excluded aneurysm sac (arrows).
systemic circulation and the excluded aneurysm sac and carry the highest risk for aneurysm rupture. Type I endoleaks can be treated with embolization or angioplasty and stenting to re-establish the attachment sites [38]. Placement of stent-graft extenders can be used to treat Types I and III endoleaks [39]. Type II endoleaks can be treated by embolization via a transarterial or translumbar approach [40]; however, controversy regarding the necessity and timing of treatment exists since many Type II endoleaks spontaneously resolve while others persist but do not result in expansion of the excluded aneurysm sac [41]. Since Type IV endoleaks are self-limited, no treatment is needed beyond correction of procedural anticoagulation. Although non-operative options for Type V have been described, open repair has been the mainstay of treatment [35].
6. Summary EVAR has replaced open repair as the mainstay of AAA treatment, primarily due to its less-invasive nature, improved patient mortality in the immediate post-operative period, and similar long-term results. However, the risk of endoleak, and delayed rupture, is a serious complication that can occur years after EVAR and requires consistent surveillance. Five types of endoleaks have been described, with their relative incidences as follows: Type II N Type I N Type III N Types IV and V. Type II endoleaks are due to retrograde flow of blood into the aneurysm sac, leading to enhancement of the peripheral aspect of the aneurysm sac; Type I endoleaks originate at stent-graft attachment leading to enhancement at the proximal or distal attachment sites; Type III endoleaks are due to mechanical failure of the graft material leading to enhancement of the surrounding stent-graft with sparing of the periphery of the excluded aneurysm sac; Type IV endoleaks are due to porosity of the graft. Type II endoleaks have been shown to be self-limited, and so repair of those is controversial; Types I and III require immediate repair as the constitute direct communications to the systemic circulation; Type IV is self-limited as well, and Type V typically necessitates open repair. Radiologists should thus be familiar with the MDCT findings of normal postoperative AAA repairs and the possible complications that can occur with respect to future graft surveillance via imaging.
References [1] Raman SP, Kamaya A, Federle M, Fishman EK. Aortoenteric fistulas: spectrum of CT findings. Abdom Imaging 2013;38(2):367–75. [2] Mathias J, Mathias E, Jausset F, et al. Aorto-enteric fistulas: a physiopathological approach and computed tomography diagnosis. Diagn Interv Imaging 2012;93(11): 840–51. [3] Lloyd-Jones D, Adams RJ, Brown TM, et al. Heart disease and stroke statistics–2010 update: a report from the American Heart Association. Circulation 2010;121(7):e46-215. [4] McPhee JT, Hill JS, Eslami MH. The impact of gender on presentation, therapy, and mortality of abdominal aortic aneurysm in the United States, 2001–2004. J Vasc Surg 2007;45(5):891–9. [5] Ghaferi AA, Birkmeyer JD, Dimick JB. Variation in hospital mortality associated with inpatient surgery. N Engl J Med 2009;361(14):1368–75. [6] Williamson WK, Nicoloff AD, Taylor LM, Moneta GL, Landry GJ, Porter JM. Functional outcome after open repair of abdominal aortic aneurysm. J Vasc Surg 2001;33(5): 913–20. [7] Parodi JC, Palmaz JC, Barone HD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms. Ann Vasc Surg 1991;5(6):491–9. [8] Lederle FA, Freischlag JA, Kyriakides TC, et al. Long-term comparison of endovascular and open repair of abdominal aortic aneurysm. N Engl J Med 2012;367(21): 1988–97. [9] Alimi YS, Chakfe N, Rivoal E, et al. Rupture of an abdominal aortic aneurysm after endovascular graft placement and aneurysm size reduction. J Vasc Surg 1998; 28(1):178–83. [10] Ramaiah VG, Thompson CS, Rodriguez-Lopez JA, DiMugno L, Olsen D, Diethrich EB. Endovascular repair of AAA rupture 20 months after endoluminal stent-grafting. J Endovasc Ther 2001;8(2):125–30. [11] Baum RA, Carpenter JP, Tuite CM, et al. Diagnosis and treatment of inferior mesenteric arterial endoleaks after endovascular repair of abdominal aortic aneurysms. Radiology 2000;215(2):409–13. [12] Iezzi R, Santoro M, Dattesi R, et al. Multi-detector CT angiographic imaging in the follow-up of patients after endovascular abdominal aortic aneurysm repair (EVAR). Insights Into Imaging 2012;3(4):313–21. [13] Veith FJ, Baum RA, Ohki T, et al. Nature and significance of endoleaks and endotension: summary of opinions expressed at an international conference. J Vasc Surg 2002;35(5):1029–35. [14] Wolf YG, Tillich M, Lee WA, Fogarty TJ, Zarins CK, Rubin GD. Changes in aneurysm volume after endovascular repair of abdominal aortic aneurysm. J Vasc Surg 2002; 36(2):305–9. [15] Armerding MD, Rubin GD, Beaulieu CF, et al. Aortic aneurysmal disease: assessment of stent-graft treatment-CT versus conventional angiography. Radiology 2000; 215(1):138–46. [16] Lawler LP, Fishman EK. Multidetector row computed tomography of the aorta and peripheral arteries. Cardiol Clin 2003;21(4):607–29. [17] Rubin GD, Shiau MC, Leung AN, Kee ST, Logan LJ, Sofilos MC. Aorta and iliac arteries: single versus multiple detector-row helical CT angiography. Radiology 2000;215(3): 670–6.
M.T. Heller et al. / Clinical Imaging 39 (2015) 367–373 [18] Platt JF, Reige KA, Ellis JH. Aortic enhancement during abdominal CT angiography: correlation with test injections, flow rates, and patient demographics. AJR Am J Roentgenol 1999;172(1):53–6. [19] Rozenblit AM, Patlas M, Rosenbaum AT, et al. Detection of endoleaks after endovascular repair of abdominal aortic aneurysm: value of unenhanced and delayed helical CT acquisitions. Radiology 2003;227(2):426–33. [20] Golzarian J, Dussaussois L, Abada HT, et al. Helical CT of aorta after endoluminal stent-graft therapy: value of biphasic acquisition. AJR Am J Roentgenol 1998; 171(2):329–31. [21] Stavropoulos SW, Charagundla SR. Imaging techniques for detection and management of endoleaks after endovascular aortic aneurysm repair. Radiology 2007; 243(3):641–55. [22] Macari M, Chandarana H, Schmidt B, Lee J, Lamparello P, Babb J. Abdominal aortic aneurysm: can the arterial phase at CT evaluation after endovascular repair be eliminated to reduce radiation dose? Radiology 2006;241(3):908–14. [23] Muller-Wille R, Borgmann T, Wohlgemuth WA, et al. Dual-energy computed tomography after endovascular aortic aneurysm repair: the role of hard plaque imaging for endoleak detection. Eur Radiol 2014;24(10):2449–57. [24] Stolzmann P, Frauenfelder T, Pfammatter T, et al. Endoleaks after endovascular abdominal aortic aneurysm repair: detection with dual-energy dual-source CT. Radiology 2008;249(2):682–91. [25] Ascenti G, Mazziotti S, Lamberto S, et al. Dual-energy CT for detection of endoleaks after endovascular abdominal aneurysm repair: usefulness of colored iodine overlay. AJR Am J Roentgenol 2011;196(6):1408–14. [26] Maintz D, Fischbach R, Juergens KU, Allkemper T, Wessling J, Heindel W. Multislice CT angiography of the iliac arteries in the presence of various stents: in vitro evaluation of artifacts and lumen visibility. Investig Radiol 2001;36(12):699–704. [27] Corriere MA, Feurer ID, Becker SY, et al. Endoleak following endovascular abdominal aortic aneurysm repair: implications for duration of screening. Ann Surg 2004; 239(6):800–5 [discussion 805–807]. [28] Stavropoulos SW, Clark TW, Carpenter JP, et al. Use of CT angiography to classify endoleaks after endovascular repair of abdominal aortic aneurysms. J Vasc Interv Radiol 2005;16(5):663–7.
373
[29] Alerci M, Oberson M, Fogliata A, Gallino A, Vock P, Wyttenbach R. Prospective, intraindividual comparison of MRI versus MDCT for endoleak detection after endovascular repair of abdominal aortic aneurysms. Eur Radiol 2009;19(5):1223–31. [30] Criado FJ, Abul-Khoudoud OR, Domer GS, et al. Endovascular repair of the thoracic aorta: lessons learned. Ann Thorac Surg 2005;80(3):857–63 [discussion 863]. [31] Chernyak V, Rozenblit AM, Patlas M, et al. Type II endoleak after endoaortic graft implantation: diagnosis with helical CT arteriography. Radiology 2006;240(3):885–93. [32] Timaran CH, Ohki T, Rhee SJ, et al. Predicting aneurysm enlargement in patients with persistent type II endoleaks. J Vasc Surg 2004;39(6):1157–62. [33] Gorich J, Rilinger N, Sokiranski R, et al. Leakages after endovascular repair of aortic aneurysms: classification based on findings at CT, angiography, and radiography. Radiology 1999;213(3):767–72. [34] Baum RA, Stavropoulos SW, Fairman RM, Carpenter JP. Endoleaks after endovascular repair of abdominal aortic aneurysms. J Vasc Interv Radiol 2003;14(9 Pt. 1):1111–7. [35] Mennander A, Pimenoff G, Heikkinen M, Partio T, Zeitlin R, Salenius JP. Nonoperative approach to endotension. J Vasc Surg 2005;42(2):194–9. [36] Sternbergh WC, Greenberg RK, Chuter TA, Tonnessen BH. Redefining postoperative surveillance after endovascular aneurysm repair: recommendations based on 5year follow-up in the US Zenith multicenter trial. J Vasc Surg 2008;48(2):278–84 [discussion 284–275]. [37] Eskandari MK, Yao JS, Pearce WH, et al. Surveillance after endoluminal repair of abdominal aortic aneurysms. Cardiovasc Surg 2001;9(5):469–71. [38] Sheehan MK, Barbato J, Compton CN, Zajko A, Rhee R, Makaroun MS. Effectiveness of coiling in the treatment of endoleaks after endovascular repair. J Vasc Surg 2004; 40(3):430–4. [39] Teruya TH, Ayerdi J, Solis MM, et al. Treatment of type III endoleak with an aortouniiliac stent graft. Ann Vasc Surg 2003;17(2):123–8. [40] Baum RA, Carpenter JP, Golden MA, et al. Treatment of type 2 endoleaks after endovascular repair of abdominal aortic aneurysms: comparison of transarterial and translumbar techniques. J Vasc Surg 2002;35(1):23–9. [41] Maldonado TS, Gagne PJ. Controversies in the management of type II "branch" endoleaks following endovascular abdominal aortic aneurysm repair. Vasc Endovasc Surg 2003;37(1):1–12.
©2015 Elsevier
Contents lists available at ScienceDirect
Clinical Imaging journal homepage: http://www.clinicalimaging.org
MDCT of endoleaks following endovascular repair of abdominal aortic aneurysms Matthew T. Heller a, Amar B. Shah b, Puneet Bhargava c, Udayan Srivastava a,⁎, Xiameng Sun a a b c
Department of Radiology, University of Pittsburgh School of Medicine, 200 Lothrop St, Suite 3950 PUH S. Tower, Pittsburgh, PA 15213 Westchester Medical Center, Department of Radiology, 100 Woods Road Room 1319, Macy Pavilion, Valhalla, NY 10595 Mail Box 358280, S-114/Radiology, VA Puget Sound Health Care System, 1660 S Columbian Way, Seattle, WA 98108
a r t i c l e
i n f o
Article history: Received 21 June 2014 Received in revised form 11 November 2014 Accepted 5 January 2015 Keywords: EVAR AAA MDCT Aneurysm Endoleak
a b s t r a c t Endovascular aneurysm repair has been used to repair abdominal aortic aneurysms but necessitates surveillance to diagnose the delayed possibility of endoleak formation. Multi-detector computer tomography (MDCT) of the abdomen is one imaging technique used to diagnose enlargement of the aneurysm sac that may be indicative of endoleaks. MDCT has a role in identifying the initial endoleak formation and providing signs suggestive of the specific endoleak subtype; thus it is necessary for radiologists to be familiar with the findings of endoleak seen on MDCT. In this pictorial review, we explore the various types of endoleaks and their appearance on MDCT. © 2015 Elsevier Inc. All rights reserved.
1. Introduction Aneurysms of the abdominal aorta (AAA) are frequently observed incidentally during multi-detector computed tomography (MDCT) of the abdomen. AAA may also present as an aorto-enteric fistula [1,2]. The incidence of abdominal aortic aneurysm increases with age; AAA is estimated to occur in up to 12.5% of men and 6% of women aged 75–84 years [3]. Annually, in the United States, over 40,000 patients undergo repair of aneurysms of the abdominal aorta [4]. AAA repair remains one of the highest risk surgical procedures, second only to colectomy for the highest number of annual perioperative deaths [5]. Historically, open surgical repair was the mainstay of treatment for aneurysms of the abdominal aorta. Although successful, the associated perioperative morbidity and often lengthy recovery time are drawbacks of the open repair [6]. Endovascular aneurysm repair (EVAR) was introduced in the early 1990s and was touted as a less invasive alternative to the traditional open aneurysm repair [7]. Over the past two decades, refinement of the EVAR technique has produced an initial survival advantage and yielded a similar long-term survival to open repair [8]. Despite these advantages, however, delayed rupture remains a concern for patients undergoing EVAR. The complication of delayed rupture is preceded by progressive aneurysm expansion that may develop despite uneventful technical
⁎ Corresponding author. University of Pittsburgh School of Medicine, Department of Radiology, 200 Lothrop St, Suite 3950 PUH S. Tower, Pittsburgh PA 15213. Tel.: +1 412 647 3550; fax: +1 412 647 7795. E-mail address: [email protected] (U. Srivastava). http://dx.doi.org/10.1016/j.clinimag.2015.01.004 0899-7071/© 2015 Elsevier Inc. All rights reserved.
performance of EVAR [9,10]. Progressive aneurysm expansion is multifactorial, but a significant contributing factor is the development of an endoleak. An endoleak is defined as blood flow external to the stentgraft but inside the aneurysm sac [11]. Certain types of endoleaks, most commonly type II endoleaks, allow the aneurysm sac to communicate with systemic circulation. When the aneurysm sac is continually exposed to the high pressures of systemic circulation, the aneurysm sac can progressively enlarge. If endoleaks are not diagnosed early, the progressive enlargement of the aneurysm sac can lead to catastrophic rupture. Therefore, patients who have undergone EVAR require imaging surveillance of the stent graft throughout their lifetime. While various imaging modalities can assess the temporal changes of the size of the aneurysm sac, MDCT is an effective and specific technique that is commonly employed [12]. Since diagnosis of endoleaks can be challenging, it is imperative for the radiologist to be familiar with the MDCT findings and their significance with respect to ramifications for treatment [13,14]. This pictorial review will illustrate and discuss the key MDCT findings of the types of endoleaks following EVAR and briefly discuss their general management.
2. MDCT technique and normal post-operative appearance MDCT angiography has evolved into a reliable imaging modality for the evaluation of patients who have undergone EVAR. MDCT is rapidly performed and has a higher sensitivity for detecting endoleaks compared with conventional catheter angiography [15]. Multi-detector technology has evolved to enable imagers to acquire thin section datasets with high spatial resolution over short acquisition periods, reducing patient motion
368
M.T. Heller et al. / Clinical Imaging 39 (2015) 367–373
artifact [16]. The decreased scan time afforded by MDCT has also allowed manipulation of the administration of intravenous contrast material using smaller volumes of contrast. In addition, advances in contrast injector design allow imager to use higher contrast flow rates allowing for better opacification of the stent graft [17,18]. Additionally, the use of bolus tracking software has contributed to improved reliability and reproducibility of MDCT. While MDCT protocols for evaluating the patient after EVAR will vary according to scanner type and institution, protocols generally consist of two or three phases of imaging [19,20]. The general components of a typical protocol may consist of non-contrast imaging and post-contrast imaging during the arterial and/or delayed venous phases [21]. However, some investigators have shown that diagnostic performance can be maintained without employing all of these phases. While the arterial phase was initially thought to aid in the detection and treatment planning of endoleaks, another study did not find the acquisition of arterial phase images to be mandatory [22]. Pre-contrast images may be considered useful in distinguishing endoleaks from focal calcification in the aneurysm sac, while the delayed venous phase can detect endoleaks with slower flow that are not apparent during the arterial phase [19,21]. However, since radiation dose increases with a higher number of phases, some centers have chosen to eliminate the non-contrast images and perform only postcontrast biphasic imaging; calcifications can still be discriminated from a leak since the hyperattenuation from iodine will decrease from the arterial to the delayed phases while the attenuation of calcium will remain constant between the two phases. Additionally, the use of dual energy CT has allowed reconstruction of virtual non-contrast images to substitute for actual image acquisition of the traditional non-contrast phase [23,24]. It has also been demonstrated that reconstruction of virtual non-contrast images and additional post-processing techniques from a single phase, dual-energy protocol significantly lowers radiation dose while maintaining extremely high diagnostic accuracy [25]. As with open repair, the goal of EVAR is to isolate flow in the aortic lumen from the aneurysm sac, to prevent further aneurysm enlargement and rupture. The EVAR procedure consists of percutaneous insertion of the collapsed stent-graft via the femoral artery, positioning with use of digital subtraction angiographic images, and deployment of the stent-graft within the aortic lumen to cover the length of the aneurysm. Stent-grafts can be made from a number of materials, including a combination of steel, nitinol or elgiloy, and a cover of plastic or polyester. On MDCT, the walls of the stent-grafts are thin (b2 mm) and hyperattenuating. Imaging artifacts from stentgrafts are generated less common with MDCT compared with magnetic resonance imaging (MRI); however, on occasion, mild streak artifact may be encountered with nitinol and elgiloy compositions [26]. The stent-graft is anchored proximally to the non-aneurysmal aspect of the abdominal aorta and distally within the common iliac arteries (Fig. 1). The proximal aspect of the stent graft consists of a single, central lumen that is opacified during contrast-enhanced MDCT. The surrounding excluded aneurysm sac consists of low attenuation thrombus; On occasion, areas of higher attenuation will be visualized and are thought to be due to dystrophic calcification of the mural thrombus, but no areas of contrast enhancement should be present normally. In the infrarenal aorta, distal to the proximal anchors of the endovascular stent graft, a ‘double lumen’ is observed due to the presence of the bifurcating limbs of the stent-graft proximal to their course within the common iliac arteries. Once the limbs enter their respective common iliac arteries, a single lumen is again observed. The proximal and distal anchors of the stentgraft make a sharp interface with the vessel lumen; a slight lumen caliber difference is often observed at the level of the anchors due to the differential size of the vessel lumen containing the stent versus the native lumen. The diameters of the excluded aneurysm sac should decrease after EVAR. During the initial post-operative MDCT, the size reduction may not be impressive depending on time elapsed since surgery; however, the diameters should tread downward over subsequent surveillance MDCT examinations. The proximal and distal anchors of the stent graft should also remain intact and be in identical anatomic positions on subsequent imaging.
3. Role of MDCT in endoleak diagnosis Estimating the precise incidence of endoleaks is difficult to determine since this information has largely been derived from single institutional studies which used various imaging technology and technique [27]. However, it is accepted that the majority of endoleaks are type II, followed by type I, and then type III. Although the cause, location and size of endoleaks can vary, the general appearance of an endoleak is similar regardless of type. An endovascular stent graft leak on MDCT shows contrast material outside of the confines of the stent-graft and within the excluded aneurysm sac. Despite MDCT's value in detecting endoleaks, it is less specific than conventional digital subtraction angiography for characterization of the type of leak [28]. The lower specificity of MDCT angiography stems from its relative inability to determine direction of blood flow, a critical component of endoleak characterization [21]. Endoleaks detected with MDCT often benefit from undergoing digital subtraction angiography to assure proper characterization since reclassification can change treatment [28]. Post-contrast MRI has also been shown to be superior for the detection of endoleaks compared with MDCT [29]. While digital subtraction angiography remains the reference standard for the characterization of endoleaks due to its higher temporal resolution and ability to determine direction of flow, it is important that the radiologist is familiar with the key MDCT findings of the different types of endoleaks and their general management (Table 1). 4. Types of endoleaks 4.1. Type I endoleaks Type I endoleaks originate at the stent-graft attachment sites due to an incomplete seal between the stent-graft and the arterial wall. This results in communication between the systemic circulation and the excluded aneurysm sac. Type I endoleaks can be classified as proximal (Type Ia) or distal (Type Ib) [13]. A third subclasification (Type Ic) denotes the rare instance when there is retrograde filling of an aneurysm in a patient who underwent simultaneous EVAR and femoral-femoral bypass with occlusion of the contralateral femoral artery; retrograde flow into the aneurysm sac occurs because of incomplete occlusion of the femoral artery. Types Ia and Ib endoleaks are most common in patients with atypical arterial anatomy (tortuosity, peripheral thrombus) and after EVAR of a thoracic aortic aneurysm [30]. An MDCT finding that is suggestive of a type I endoleak is the presence of abnormal enhancement that abuts or communicates with the proximal or distal attachment sites (Fig. 2). If the endoleak is sufficiently large, the leaked blood may dissect away from the anchors and into the central aspect of the excluded aneurysm sac. In these cases, it may be especially difficult to differentiate a type I endoleak from type II and III endoleaks on MDCT, requiring digital subtraction angiography for clarification. Large type I leaks resulting in build-up of high pressure between the aortic wall and the stent-graft can result in a mural tear of the aorta at the level of the attachment site. 4.2. Type II endoleaks Type II endoleaks are the most common type of endoleak and are due to retrograde flow of blood into the aneurysm sac. Retrograde blood flow most commonly occurs through various aortic branch vessels such as the lumbar arteries and inferior mesenteric artery. Retrograde flow through these vessels re-establishes communication between the excluded aneurysm sac and systemic circulation. During MDCT angiography, a Type II endoleak typically appears as enhancement in the peripheral aspect of the aneurysm sac (Fig. 3) [31]. If the abnormal enhancement is located in the anterior aspect of the excluded aneurysm sac, the supply may be from the inferior mesenteric artery while a posterior location implies supply from a lumbar artery. The presence of contrast within the inferior mesenteric or lumbar arteries is not
M.T. Heller et al. / Clinical Imaging 39 (2015) 367–373
369
Fig. 1. Abdominal aortic aneurysm before and after EVAR. (A) Volume rendered 3-dimensional reconstructed image in a patient with a fusiform AAA (arrow). (B) After EVAR, the volume rendered image shows the bifurcating stent-graft (arrow) and the borders of the excluded aneurysm sac (arrowheads). (C) Axial enhanced MDCT during the late arterial phase shows the AAA prior to repair. (D) Following EVAR, the axial enhanced MDCT during the arterial phase shows flow in the lumen of the stent-graft (arrow) and no flow within the excluded aneurysm sac (arrowheads). (E) More inferiorly, an axial enhanced MDCT image during the late arterial phase shows the largest transverse section of the AAA (arrowheads) prior to repair. (F) Following EVAR, the axial enhanced MDCT during the arterial phase demonstrates that contrast opacifies two lumens (arrows) due to the bifurcating limbs of the stent graft. There is no flow in the excluded aneurysm sac (arrowheads). (G) Axial enhanced MDCT during the late arterial phase shows the heavily calcified right common iliac artery (arrow) and tapering of the AAA prior to repair. (H) Following EVAR, the axial enhanced MDCT during the arterial phase demonstrates that the distal anchors of the stent-graft extend into the right common iliac artery (arrow). There is absence of flow in the excluded aneurysm sac (arrowhead).
Table 1 Endoleak classification and summary Endoleak classification summary
Location Etiology Key MDCT finding
Significance Treatment
Type 1
Type 2
Type 3
Type 4
Type 5
Proximal (1a) or distal (1b) anchors Incomplete seal between graft and vessel wall Contrast in excluded aneurysm sac which is continuous with attachment sites
Insertion of aortic branch vessels
Variable, but typically occur centrally Component separation or tear of graft material Contrast in central aspect of excluded aneurysm sac away from attachment sites and branch vessel insertions High pressure endoleak → high risk of rupture Urgent angiographic evaluation/intervention
Diffuse
Unknown
Porosity of graft material
Potential occult defect in graft Continued enlargement of excluded aneurysm sac without radiographic identification of a leak
High pressure endoleak → high risk of rupture Urgent angiographic evaluation/intervention
Retrograde flow via aortic branch vessels. Contrast in excluded aneurysm sac located peripherally at site of branch artery insertion (i.e.-lumbar or inferior mesenteric arteries) Less pressure than Types 1 or 3—may close spontaneously; Treatment if increasing size of aneurysm sac or symptoms
Transiently observed during endovascular procedure; no MDCT findings Resolve after cessation of anticoagulation None
Low risk in short-term Angiography to evaluate for occult leak; surgery if enlarging
370
M.T. Heller et al. / Clinical Imaging 39 (2015) 367–373
Fig. 2. Type I endoleak. Axial enhanced MDCT during the arterial phase in a patient presenting with left flank pain and hypotension. (A) The image demonstrates abnormal flow (arrow) posterior to the superior margin of the proximal anchors of the stent-graft. There is extensive hematoma (arrowheads) in the left aspect of the retroperitoneum. (B) More inferiorly, the axial enhanced MDCT image reveals that the abnormal flow (arrow) enters the excluded aneurysm sac. The retroperitoneal hematoma (arrowheads) is due to rupture of the excluded aneurysm sac. (C) Volume rendered 3-dimensional image demonstrates the site of endoleak (arrow) at the level of the proximal anchors and extension of leaked blood (arrowhead) into the excluded aneurysm sac. (D) Surgical specimen shows a defect in the stent-graft near the proximal anchors.
specific for a Type II endoleak. Contrast in these vessels can theoretically be due to inflow from retrograde flow, a Type II endoleak, or outflow from Type I or III endoleaks. Although peripheral location of abnormal enhancement within the excluded aneurysm sac during MDCT is suggestive of a Type II leak, definitive characterization with digital subtraction angiography would be needed to establish the direction of flow [21]. The size of a suspected type II endoleak should be accurately reported
since those larger than 15 mm have been associated with aneurysm expansion [32]. 4.3. Type III endoleaks Type III endoleaks are relatively uncommon and result from mechanical failure of the graft material. Failure can occur in the form of
Fig. 3. Type II endoleak. Axial enhanced MDCT during the arterial phase in a patient presenting for routine surveillance following EVAR. (A) The image shows enhancement within the posterior aspect of the excluded aneurysm sac (arrow) due to retrograde flow from a lumbar artery (arrowhead). (B) More inferiorly, leaked contrast (arrow) accumulates in the posterior aspect of the excluded aneurysm sac.
M.T. Heller et al. / Clinical Imaging 39 (2015) 367–373
371
fracture, junctional separations, or focal defects from corrosion or tear of the stent-graft fabric. Potential etiologies for stent-graft failure include repetitive mechanical stresses from arterial pulsations, movement and shrinkage of the excluded aneurysm sac. An MDCT finding associated with type III endoleaks is abnormal enhancement surrounding the stent-graft with sparing of the periphery of the excluded aneurysm sac [33]. If this finding is present, the stent-graft should be carefully evaluated for a focal defect. Additionally, the presence of focal enhancement adjacent to a junction point should raise concern for a type III endoleak (Fig. 4).
phenomenon is referred to as endotension; potential etiologies include the presence of a co-existing occult endoleak (Type I, II or III), filtration of blood through the stent-graft fabric or an ineffective barrier to pressure transmission [34,35]. The MDCT finding is progressive expansion of the excluded aneurysm sac (Fig. 5). In such cases, further evaluation with other imaging modalities (magnetic resonance angiography, ultrasound, or angiography) is recommended to thoroughly exclude an endoleak that is occult on MDCT.
4.4. Type IV endoleaks
No consensus criteria have been established for the frequency of surveillance imaging for patients who have undergone EVAR. While various guidelines have been proposed, institutional variability persists [36]. Most recommendations for patients who have undergone EVAR employ surveillance MDCT and radiography at regular intervals; the frequency of surveillance increases for patients with types II and V endoleaks, while types I and III generally undergo treatment at the time of diagnosis [37]. Additionally, since endoleaks have been reported to occur as long as 7 years after EVAR, there are no established criteria for reduction of frequency of surveillance imaging for patients who remain without an endoleak years after surgery [27]. Treatment of endoleaks is determined by the type of endoleak present. Types I and III endoleaks are treated immediately after diagnosis since these types constitute a direct communication between the
Type IV endoleaks are due to the porosity of the stent-graft material and have no MDCT findings. Type IV endoleaks are observed as a transient blush of contrast within the excluded aneurysm sac. This phenomenon is observed in the angiography suite immediately following placement of the stent-graft while the patient is anticoagulated. Since type IV endoleaks are self-limited, no treatment or additional followup is required beyond the usual surveillance imaging. 4.5. Type V endoleaks Type V endoleaks are defined as expansion of the excluded aneurysm sac without identification of another type of endoleak. This
5. Follow-up imaging and treatment
Fig. 4. Type III endoleak. Axial enhanced MDCT during the arterial phase in a patient presenting for routine surveillance following EVAR. (A) The image shows a large collection of leaked contrast (arrow) within the excluded aneurysm sac. Coronal (B) and sagittal (C) enhanced MDCT during the arterial phase demonstrate that the endoleak (arrow) originates from the left iliac junction point (arrowhead) of the stent-graft. (D) Digital subtraction angiogram shows a catheter in the left iliac artery and a contained leak at the junction of the left limb.
372
M.T. Heller et al. / Clinical Imaging 39 (2015) 367–373
Fig. 5. Type V endoleak. Volume rendered 3-dimensional MDCT reconstruction in a patient presenting for routine surveillance following EVAR. (A) The image shows a relatively small caliber of the excluded aneurysm sac (arrowheads). (B) Six months later, there has been substantial enlargement of the excluded aneurysm sac (arrows).
systemic circulation and the excluded aneurysm sac and carry the highest risk for aneurysm rupture. Type I endoleaks can be treated with embolization or angioplasty and stenting to re-establish the attachment sites [38]. Placement of stent-graft extenders can be used to treat Types I and III endoleaks [39]. Type II endoleaks can be treated by embolization via a transarterial or translumbar approach [40]; however, controversy regarding the necessity and timing of treatment exists since many Type II endoleaks spontaneously resolve while others persist but do not result in expansion of the excluded aneurysm sac [41]. Since Type IV endoleaks are self-limited, no treatment is needed beyond correction of procedural anticoagulation. Although non-operative options for Type V have been described, open repair has been the mainstay of treatment [35].
6. Summary EVAR has replaced open repair as the mainstay of AAA treatment, primarily due to its less-invasive nature, improved patient mortality in the immediate post-operative period, and similar long-term results. However, the risk of endoleak, and delayed rupture, is a serious complication that can occur years after EVAR and requires consistent surveillance. Five types of endoleaks have been described, with their relative incidences as follows: Type II N Type I N Type III N Types IV and V. Type II endoleaks are due to retrograde flow of blood into the aneurysm sac, leading to enhancement of the peripheral aspect of the aneurysm sac; Type I endoleaks originate at stent-graft attachment leading to enhancement at the proximal or distal attachment sites; Type III endoleaks are due to mechanical failure of the graft material leading to enhancement of the surrounding stent-graft with sparing of the periphery of the excluded aneurysm sac; Type IV endoleaks are due to porosity of the graft. Type II endoleaks have been shown to be self-limited, and so repair of those is controversial; Types I and III require immediate repair as the constitute direct communications to the systemic circulation; Type IV is self-limited as well, and Type V typically necessitates open repair. Radiologists should thus be familiar with the MDCT findings of normal postoperative AAA repairs and the possible complications that can occur with respect to future graft surveillance via imaging.
References [1] Raman SP, Kamaya A, Federle M, Fishman EK. Aortoenteric fistulas: spectrum of CT findings. Abdom Imaging 2013;38(2):367–75. [2] Mathias J, Mathias E, Jausset F, et al. Aorto-enteric fistulas: a physiopathological approach and computed tomography diagnosis. Diagn Interv Imaging 2012;93(11): 840–51. [3] Lloyd-Jones D, Adams RJ, Brown TM, et al. Heart disease and stroke statistics–2010 update: a report from the American Heart Association. Circulation 2010;121(7):e46-215. [4] McPhee JT, Hill JS, Eslami MH. The impact of gender on presentation, therapy, and mortality of abdominal aortic aneurysm in the United States, 2001–2004. J Vasc Surg 2007;45(5):891–9. [5] Ghaferi AA, Birkmeyer JD, Dimick JB. Variation in hospital mortality associated with inpatient surgery. N Engl J Med 2009;361(14):1368–75. [6] Williamson WK, Nicoloff AD, Taylor LM, Moneta GL, Landry GJ, Porter JM. Functional outcome after open repair of abdominal aortic aneurysm. J Vasc Surg 2001;33(5): 913–20. [7] Parodi JC, Palmaz JC, Barone HD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms. Ann Vasc Surg 1991;5(6):491–9. [8] Lederle FA, Freischlag JA, Kyriakides TC, et al. Long-term comparison of endovascular and open repair of abdominal aortic aneurysm. N Engl J Med 2012;367(21): 1988–97. [9] Alimi YS, Chakfe N, Rivoal E, et al. Rupture of an abdominal aortic aneurysm after endovascular graft placement and aneurysm size reduction. J Vasc Surg 1998; 28(1):178–83. [10] Ramaiah VG, Thompson CS, Rodriguez-Lopez JA, DiMugno L, Olsen D, Diethrich EB. Endovascular repair of AAA rupture 20 months after endoluminal stent-grafting. J Endovasc Ther 2001;8(2):125–30. [11] Baum RA, Carpenter JP, Tuite CM, et al. Diagnosis and treatment of inferior mesenteric arterial endoleaks after endovascular repair of abdominal aortic aneurysms. Radiology 2000;215(2):409–13. [12] Iezzi R, Santoro M, Dattesi R, et al. Multi-detector CT angiographic imaging in the follow-up of patients after endovascular abdominal aortic aneurysm repair (EVAR). Insights Into Imaging 2012;3(4):313–21. [13] Veith FJ, Baum RA, Ohki T, et al. Nature and significance of endoleaks and endotension: summary of opinions expressed at an international conference. J Vasc Surg 2002;35(5):1029–35. [14] Wolf YG, Tillich M, Lee WA, Fogarty TJ, Zarins CK, Rubin GD. Changes in aneurysm volume after endovascular repair of abdominal aortic aneurysm. J Vasc Surg 2002; 36(2):305–9. [15] Armerding MD, Rubin GD, Beaulieu CF, et al. Aortic aneurysmal disease: assessment of stent-graft treatment-CT versus conventional angiography. Radiology 2000; 215(1):138–46. [16] Lawler LP, Fishman EK. Multidetector row computed tomography of the aorta and peripheral arteries. Cardiol Clin 2003;21(4):607–29. [17] Rubin GD, Shiau MC, Leung AN, Kee ST, Logan LJ, Sofilos MC. Aorta and iliac arteries: single versus multiple detector-row helical CT angiography. Radiology 2000;215(3): 670–6.
M.T. Heller et al. / Clinical Imaging 39 (2015) 367–373 [18] Platt JF, Reige KA, Ellis JH. Aortic enhancement during abdominal CT angiography: correlation with test injections, flow rates, and patient demographics. AJR Am J Roentgenol 1999;172(1):53–6. [19] Rozenblit AM, Patlas M, Rosenbaum AT, et al. Detection of endoleaks after endovascular repair of abdominal aortic aneurysm: value of unenhanced and delayed helical CT acquisitions. Radiology 2003;227(2):426–33. [20] Golzarian J, Dussaussois L, Abada HT, et al. Helical CT of aorta after endoluminal stent-graft therapy: value of biphasic acquisition. AJR Am J Roentgenol 1998; 171(2):329–31. [21] Stavropoulos SW, Charagundla SR. Imaging techniques for detection and management of endoleaks after endovascular aortic aneurysm repair. Radiology 2007; 243(3):641–55. [22] Macari M, Chandarana H, Schmidt B, Lee J, Lamparello P, Babb J. Abdominal aortic aneurysm: can the arterial phase at CT evaluation after endovascular repair be eliminated to reduce radiation dose? Radiology 2006;241(3):908–14. [23] Muller-Wille R, Borgmann T, Wohlgemuth WA, et al. Dual-energy computed tomography after endovascular aortic aneurysm repair: the role of hard plaque imaging for endoleak detection. Eur Radiol 2014;24(10):2449–57. [24] Stolzmann P, Frauenfelder T, Pfammatter T, et al. Endoleaks after endovascular abdominal aortic aneurysm repair: detection with dual-energy dual-source CT. Radiology 2008;249(2):682–91. [25] Ascenti G, Mazziotti S, Lamberto S, et al. Dual-energy CT for detection of endoleaks after endovascular abdominal aneurysm repair: usefulness of colored iodine overlay. AJR Am J Roentgenol 2011;196(6):1408–14. [26] Maintz D, Fischbach R, Juergens KU, Allkemper T, Wessling J, Heindel W. Multislice CT angiography of the iliac arteries in the presence of various stents: in vitro evaluation of artifacts and lumen visibility. Investig Radiol 2001;36(12):699–704. [27] Corriere MA, Feurer ID, Becker SY, et al. Endoleak following endovascular abdominal aortic aneurysm repair: implications for duration of screening. Ann Surg 2004; 239(6):800–5 [discussion 805–807]. [28] Stavropoulos SW, Clark TW, Carpenter JP, et al. Use of CT angiography to classify endoleaks after endovascular repair of abdominal aortic aneurysms. J Vasc Interv Radiol 2005;16(5):663–7.
373
[29] Alerci M, Oberson M, Fogliata A, Gallino A, Vock P, Wyttenbach R. Prospective, intraindividual comparison of MRI versus MDCT for endoleak detection after endovascular repair of abdominal aortic aneurysms. Eur Radiol 2009;19(5):1223–31. [30] Criado FJ, Abul-Khoudoud OR, Domer GS, et al. Endovascular repair of the thoracic aorta: lessons learned. Ann Thorac Surg 2005;80(3):857–63 [discussion 863]. [31] Chernyak V, Rozenblit AM, Patlas M, et al. Type II endoleak after endoaortic graft implantation: diagnosis with helical CT arteriography. Radiology 2006;240(3):885–93. [32] Timaran CH, Ohki T, Rhee SJ, et al. Predicting aneurysm enlargement in patients with persistent type II endoleaks. J Vasc Surg 2004;39(6):1157–62. [33] Gorich J, Rilinger N, Sokiranski R, et al. Leakages after endovascular repair of aortic aneurysms: classification based on findings at CT, angiography, and radiography. Radiology 1999;213(3):767–72. [34] Baum RA, Stavropoulos SW, Fairman RM, Carpenter JP. Endoleaks after endovascular repair of abdominal aortic aneurysms. J Vasc Interv Radiol 2003;14(9 Pt. 1):1111–7. [35] Mennander A, Pimenoff G, Heikkinen M, Partio T, Zeitlin R, Salenius JP. Nonoperative approach to endotension. J Vasc Surg 2005;42(2):194–9. [36] Sternbergh WC, Greenberg RK, Chuter TA, Tonnessen BH. Redefining postoperative surveillance after endovascular aneurysm repair: recommendations based on 5year follow-up in the US Zenith multicenter trial. J Vasc Surg 2008;48(2):278–84 [discussion 284–275]. [37] Eskandari MK, Yao JS, Pearce WH, et al. Surveillance after endoluminal repair of abdominal aortic aneurysms. Cardiovasc Surg 2001;9(5):469–71. [38] Sheehan MK, Barbato J, Compton CN, Zajko A, Rhee R, Makaroun MS. Effectiveness of coiling in the treatment of endoleaks after endovascular repair. J Vasc Surg 2004; 40(3):430–4. [39] Teruya TH, Ayerdi J, Solis MM, et al. Treatment of type III endoleak with an aortouniiliac stent graft. Ann Vasc Surg 2003;17(2):123–8. [40] Baum RA, Carpenter JP, Golden MA, et al. Treatment of type 2 endoleaks after endovascular repair of abdominal aortic aneurysms: comparison of transarterial and translumbar techniques. J Vasc Surg 2002;35(1):23–9. [41] Maldonado TS, Gagne PJ. Controversies in the management of type II "branch" endoleaks following endovascular abdominal aortic aneurysm repair. Vasc Endovasc Surg 2003;37(1):1–12.
©2015 Elsevier