DOI: 10.1148/radiol.2253011806
(Radiology 2002;225:845-851.)
© RSNA, 2002
Application of Duplex US for Characterization of Endoleaks in Abdominal Aortic Stent-Grafts: Report of Five Cases1
Antje L. Greenfield, MD,
Ethan J. Halpern, MD,
Joseph Bonn, MD,
Richard J. Wechsler, MD and
Mark B. Kahn, MD
1 From the Departments of Radiology (A.L.G., E.J.H., J.B., R.J.W.) and Surgery (M.B.K.), Thomas Jefferson University Hospital, Philadelphia, Pa. Received November 8, 2001; revision requested December 27; revision received April 12, 2002; accepted May 24. Address correspondence to A.L.G., 923 Mill Creek Rd, Gladwyne, PA 19035 (e-mail: antje.greenfield@mail.tju.edu).
 |
ABSTRACT
|
|---|
Endoleaks were detected with helical computed tomographic (CT) angiography in five patients after placement of an aortobiliac stent-graft. The leaks were subsequently evaluated with duplex ultrasonography (US) and, in four patients, with conventional aortography as well. CT angiography revealed a total of seven endoleaks, all of which were prospectively classified as reconstitution (type II) leaks. Duplex US demonstrated six of the seven endoleaks. At duplex US, two of the leaks were characterized as attachment-site (type I) leaks; these two diagnoses were confirmed during subsequent angiography and profoundly altered clinical care. As an adjunct to CT angiography in evaluating endoleaks, duplex US provides hemodynamic information that enables further characterization of the type of endoleak and facilitates appropriate clinical care.
© RSNA, 2002
Index terms: Aneurysm, aortic, 943.73 • Aorta, grafts and prostheses, 943.1268 • Computed tomography (CT), angiography, 943.12912 • Ultrasound (US), Doppler studies, 943.12984
|
INTRODUCTION
|
|---|
Endovascular stent-graft repair of abdominal aortic aneurysms (AAAs) is an emerging, minimally invasive alternative to open surgical repair (1–5). The goal of endovascular treatment is to achieve complete exclusion of the aneurysm sac by deploying a graft device within the abdominal aorta (6). The aneurysm sac is excluded from exposure to systemic pressures; thereby its risk of rupture is reduced. Although the delivery systems and stent-grafts used in endovascular repair have been refined over the past several years, postoperative endoleak continues to represent a common complication, limiting the success of stent-graft repair (7).
Endoleaks are defined as areas of persistent blood flow outside the lumen of the endograft but within the aneurysm sac or within connected vascular segments bypassed by the graft (7). Endoleaks may result from failure to obtain a complete seal at a proximal or distal graft attachment site (type I endoleak) or because of retrograde reconstitution of the excluded aneurysmal portion of the aorta from collateral arterial branches (type II endoleak) (7). Less common causes of endoleak include graft disruption (type III endoleak) and graft porosity (type IV endoleak) (8). The treatment of an endoleak varies according to its type. Furthermore, the classification of an endoleak often determines the decision of whether it should be aggressively repaired or conservatively monitored. Attachment-site endoleaks are generally repaired immediately. Small reconstitution endoleaks may be observed since many of them will occlude spontaneously (7,9).
Both computed tomographic (CT) angiography and duplex ultrasonography (US) are used to evaluate and monitor endoleaks after endoluminal repair of an AAA (9–12). There is no single imaging examination that has been universally accepted as the standard for the diagnosis of endoleaks. Examinations performed to screen patients for endoleaks after stent-graft placement commonly include contrast material–enhanced CT angiography (11,13–16). CT angiography is an operator-independent, reproducible examination and is not limited by the presence of bowel gas, which is often a problem for duplex US in the early postoperative period.
Recognized limitations of serial CT angiographic examinations include repeated radiation exposure, the need to use intravenous contrast material, and their relatively high cost (11). In addition, CT angiography does not depict the velocity or direction of blood flow and may not provide information regarding the origin and mechanism of an endoleak. The purpose of our study was to evaluate whether the use of duplex US alters diagnosis and clinical management of endoleaks that arise as complications of abdominal aortic stent-graft placement after such leaks have been observed at CT angiography.
|
Patients and Imaging
|
|---|
Patients
Between September 2000 and January 2001, 11 patients underwent endoluminal repair of an AAA with the Ancure aortobiliac stent-graft (Guidant, Menlo Park, Calif) at our institution. Of these 11 patients, five were found to have an endoleak that was identified and prospectively characterized at postoperative CT angiography. These five patients constitute our study population. The patients were all men and ranged in age from 70 to 80 years, with a mean age of 74 years. Four of these five patients subsequently underwent conventional aortography for definitive diagnosis and potential treatment of the endoleak. In the fifth patient, a small type II leak was demonstrated with CT angiography and duplex US. Because a 6-month follow-up CT angiogram in this patient indicated resolution of the leak, aortography was not performed.
This prospective study remains in progress and is performed with approval of the institutional review board of Thomas Jefferson University (5). Written informed consent was obtained from each patient prior to enrollment in the study.
Imaging
Our routine clinical protocol after uncomplicated placement of a stent-graft included contrast-enhanced CT angiography at 1 month and 6 months. All patients found to have an endoleak at CT angiography were subsequently examined with duplex US within 1 week after the CT angiographic examination. Final assessment of vascular anatomy was achieved with conventional aortography and in consultation with the referring vascular surgeon in four of the five patients.
Triphasic CT angiography was performed in all patients with a Hi-Speed Advantage helical scanner (GE Medical Systems; Milwaukee, Wis). First, scanning through the abdomen and pelvis was performed before the administration of contrast material.
Second, scans were obtained after intravenous infusion of a nonionic contrast medium (Optiray 320; Mallinckrodt, St Louis, Mo) with a power injector at 4 mL/sec to a total of 150 mL. The images were obtained at peak arterial enhancement in the abdominal aorta, as determined by administration of a 20-mL timing bolus of contrast material before contrast-enhanced scanning. Images were acquired with 3-mm collimation to include the entire stent-graft and attachment sites and were reconstructed every 2 mm with a 22-cm field of view.
Third, delayed scanning was performed approximately 90 seconds after contrast material injection in 5-mm sections that included the entire abdominal aorta and pelvic arterial vasculature to the inguinal level. Transverse images and multiplanar curved reformatted images were evaluated by a radiologist with expertise in cross-sectional vascular imaging. The radiologist completed a standardized post–stent placement evaluation form that specified the presence, type, and location of endoleaks; the native diameter of the AAA; the patency of the graft; the presence of any graft thrombus; any problems with graft integrity or kinking; the appearance of the attachment site; and the patency of the lumbar arteries or the inferior mesenteric artery (IMA).
Duplex US was performed with a Sequoia 512 system (Acuson, Mountain View, Calif) to enable identification of each leak and evaluation of its origin. A wideband curved linear array transducer, the 6C2 (Acuson), was used to perform gray-scale and Doppler imaging. This transducer enables fundamental gray-scale imaging with a center frequency that can be varied from 2.5 MHz to 6.0 MHz and enables harmonic imaging at frequencies of 4.0 MHz to 5.0 MHz. Duplex US examinations were performed jointly by two board-certified radiologists (A.L.G., E.J.H.) with additional fellowship training in US who were aware of the results of CT angiography.
The abdominal aorta was evaluated with a standard protocol that included the acquisition of transverse and sagittal images with gray-scale and color Doppler US. The largest anteroposterior and transverse diameters of the aneurysm were recorded. An attempt was made to image the proximal and distal graft attachment sites, as well as the IMA, in each patient. Attention was focused on each endoleak demonstrated with CT angiography. Each endoleak was first visualized with color Doppler US imaging of blood flow outside the graft lumen but within the native aortic lumen. The leak was then traced to its origin. Spectral Doppler waveform analysis was performed to complete the evaluation.
US findings regarding the presence, location, and type of the endoleak were compared with findings at CT and conventional aortography. When duplex US results were discrepant with CT angiographic results in terms of the type of endoleak, we sought to determine which modality—CT angiography or duplex US—most correctly depicted the endoleak when results of these examinations were correlated with aortographic results. We also sought to determine how further characterization of each endoleak with duplex US subsequently altered clinical management of the endoleak.
Digital aortography of the abdomen was performed with a Philips V5000 unit (Philips Medical Systems, Bothell, Wash) in four of the five patients. The angiographers were aware of all CT angiographic and duplex US findings at the time of aortography. The presence, location, and type of each endoleak at aortography were recorded and compared with findings at CT angiography and duplex US. Since aortographic findings dominated subsequent clinical decisions about further management and treatment of the endoleaks, this imaging technique was considered the standard of reference for the purposes of our study. The clinical management plan created on the basis of CT angiographic findings was compared with the management plan suggested after duplex US and with the actual management decisions made after aortography.
|
Case Results
|
|---|
Duplex US revealed six of seven endoleaks demonstrated at CT angiography in five patients (ie, there was one false-negative duplex US result). In one patient, an additional leak was found with duplex US. This leak was not identified prospectively at CT angiography but was present on retrospective evaluation of the CT angiograms. All leaks seen at CT angiography were classified prospectively as reconstitution leaks—four were thought to arise from lumbar arteries and three were thought to arise from the IMA. No attachment-site leaks were diagnosed prospectively at CT angiography.
In two patients, the origin of three leaks was correctly identified at duplex US. These leaks were confirmed at subsequent aortography to be two distal attachment-site leaks and one reconstitution leak arising from the IMA. These two patients are described in greater detail below.
In a third patient, duplex US depicted two sites of blood flow that were outside the graft, within the AAA, and adjacent to the graft material. The flow pattern was turbulent and complex and did not have a dominant direction. No connection of blood flow to the native aortic wall, patent lumbar arteries, or IMA was seen. On the basis of this appearance, two very small endoleaks, possibly caused by porosity of the graft material, were thought to be present. Subsequent aortography in this patient revealed a single reconstitution leak from a lumbar artery, as predicted at CT angiography.
CT angiography in a fourth patient revealed a type II leak arising from a lumbar artery. Duplex US revealed a patent lumbar artery with retrograde blood flow into the native aorta; this finding confirmed the suspected type II leak. This patient did not undergo conventional aortography but was followed up at 6 months with CT angiography, which revealed that this leak had resolved in a manner typical of that of type II endoleaks.
In a fifth patient, a complex leak (ie, multiple type II leaks) was identified at CT angiography. Duplex US depicted a large leak in the proximal portion of the aneurysm in the native aorta, in the vicinity of the aortic attachment site of the graft. The possibility of a proximal attachment-site leak was considered. However, the origin of the leak was posterior to the stent-graft, and spectral waveform analysis showed turbulent arterial flow with a slow upstroke pattern suggestive of a reconstitution leak from a high lumbar artery. This leak was not visualized at conventional aortography. On the basis of the duplex US results, additional angiographic imaging, particularly of the proximal attachment site, was performed, but no leak was visualized.
Treatment of three patients was directed and altered on the basis of duplex US findings. The first two patients described in this section underwent endovascular treatment for type I leaks characterized with duplex US, while the patient with no visible leak at conventional aortography continues to be followed up closely. The utility of US in diagnosis is well illustrated by the cases of the first two patients described in this section:
A reconstitution endoleak from the IMA (a type II leak) was diagnosed in one patient at CT angiography (Fig 1a). Duplex US depicted a type I distal attachment-site leak in the left iliac limb. Blood flow was retrograde outside the iliac graft limb (Fig 1b), with antegrade blood flow in the IMA representing an egress (Fig 1c). The antegrade direction of flow in the IMA was not compatible with the diagnosis of a type II leak suggested at CT angiography. Findings at aortography confirmed a type I distal attachment-site leak (Fig 1d), and successful endoluminal repair was performed, with placement of a Wallgraft device (Boston Scientific, Boston, Mass) at the leaking graft attachment site.
View larger version (138K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1a. Images in a 70-year-old man with a bifurcated aortic stent-graft placed for treatment of an infrarenal AAA and a separate left common iliac artery aneurysm. (a) Transverse CT angiogram at the level of the origin of the patent enhancing IMA (open arrowhead). Extravasation of contrast material within the native aorta (solid arrowheads) is seen anterior to the patent limbs (arrows) of the stent-graft. The graft attachment sites (not shown) were normal. (b) Conventional aortogram in an anterior oblique projection shows double intensity of contrast enhancement, with contrast material visible inside and outside of the graft. A type I leak is depicted at the distal left iliac graft attachment site (open arrowheads); the leak extends along the aorta (solid arrowheads). (c) Sagittal duplex US image of the distal left common iliac attachment site shows retrograde flow from the distal iliac graft limb (solid arrowheads) into the native common iliac artery outside the graft (open arrowheads); these findings are suggestive of a type I leak (arrow). (d) Transverse duplex US image at the same level as c shows a patent IMA (arrow) with antegrade flow (above baseline) on the spectral Doppler waveform.
|
|
View larger version (100K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1b. Images in a 70-year-old man with a bifurcated aortic stent-graft placed for treatment of an infrarenal AAA and a separate left common iliac artery aneurysm. (a) Transverse CT angiogram at the level of the origin of the patent enhancing IMA (open arrowhead). Extravasation of contrast material within the native aorta (solid arrowheads) is seen anterior to the patent limbs (arrows) of the stent-graft. The graft attachment sites (not shown) were normal. (b) Conventional aortogram in an anterior oblique projection shows double intensity of contrast enhancement, with contrast material visible inside and outside of the graft. A type I leak is depicted at the distal left iliac graft attachment site (open arrowheads); the leak extends along the aorta (solid arrowheads). (c) Sagittal duplex US image of the distal left common iliac attachment site shows retrograde flow from the distal iliac graft limb (solid arrowheads) into the native common iliac artery outside the graft (open arrowheads); these findings are suggestive of a type I leak (arrow). (d) Transverse duplex US image at the same level as c shows a patent IMA (arrow) with antegrade flow (above baseline) on the spectral Doppler waveform.
|
|
View larger version (107K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1c. Images in a 70-year-old man with a bifurcated aortic stent-graft placed for treatment of an infrarenal AAA and a separate left common iliac artery aneurysm. (a) Transverse CT angiogram at the level of the origin of the patent enhancing IMA (open arrowhead). Extravasation of contrast material within the native aorta (solid arrowheads) is seen anterior to the patent limbs (arrows) of the stent-graft. The graft attachment sites (not shown) were normal. (b) Conventional aortogram in an anterior oblique projection shows double intensity of contrast enhancement, with contrast material visible inside and outside of the graft. A type I leak is depicted at the distal left iliac graft attachment site (open arrowheads); the leak extends along the aorta (solid arrowheads). (c) Sagittal duplex US image of the distal left common iliac attachment site shows retrograde flow from the distal iliac graft limb (solid arrowheads) into the native common iliac artery outside the graft (open arrowheads); these findings are suggestive of a type I leak (arrow). (d) Transverse duplex US image at the same level as c shows a patent IMA (arrow) with antegrade flow (above baseline) on the spectral Doppler waveform.
|
|
View larger version (86K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 1d. Images in a 70-year-old man with a bifurcated aortic stent-graft placed for treatment of an infrarenal AAA and a separate left common iliac artery aneurysm. (a) Transverse CT angiogram at the level of the origin of the patent enhancing IMA (open arrowhead). Extravasation of contrast material within the native aorta (solid arrowheads) is seen anterior to the patent limbs (arrows) of the stent-graft. The graft attachment sites (not shown) were normal. (b) Conventional aortogram in an anterior oblique projection shows double intensity of contrast enhancement, with contrast material visible inside and outside of the graft. A type I leak is depicted at the distal left iliac graft attachment site (open arrowheads); the leak extends along the aorta (solid arrowheads). (c) Sagittal duplex US image of the distal left common iliac attachment site shows retrograde flow from the distal iliac graft limb (solid arrowheads) into the native common iliac artery outside the graft (open arrowheads); these findings are suggestive of a type I leak (arrow). (d) Transverse duplex US image at the same level as c shows a patent IMA (arrow) with antegrade flow (above baseline) on the spectral Doppler waveform.
|
|
This patient returned for subsequent follow-up CT angiography, which revealed a recurrent endoleak but did not clearly depict its origin (Fig 2a). Duplex US depicted a large type II reconstitution leak from the IMA with predominantly retrograde flow within the artery (Fig 2b, 2c). These findings were confirmed with aortography (Fig 2d). Because of the size of the patent IMA and the recurrence of the endoleak, coil embolization of the IMA was performed.
View larger version (147K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2a. Follow-up images obtained in the same patient as in Figure 1 after repair of the type I leak. (a) Transverse CT angiogram at the level of the origin of the small, patent, and enhancing IMA (open arrowhead). A recurrent small endoleak (solid arrowheads) appears as an area of faint contrast enhancement within the native aorta, anterior to the patent limbs of the stent-graft (arrows). (b) Conventional aortogram in an anterior oblique projection shows retrograde reconstitution of the IMA (open arrowhead) through the arc of Riolan; a focal, small collection of contrast material (solid arrowhead) is seen outside the graft and inside the aneurysm in the native aorta. (c) Transverse duplex US image shows a patent IMA (arrowheads) with a complex flow pattern on the spectral waveform. There is a short segment of early systolic antegrade flow (below baseline) followed by a dominant late systolic retrograde flow component (represented by an above-baseline component directed toward the transducer, but reversing to the direction of blood flow expected in a normal IMA). The early antegrade component may be related to transmitted pulsations from the endograft. The graft expands during systole and thus creates a propulsive effect on residual blood pooling in the native aorta adjacent to the graft. Once the collateral vessels fill the IMA in retrograde fashion in late systole, the dominant retrograde flow becomes apparent. The late retrograde component of the spectral waveform represents the endoleak flow entering back into the aorta. (d) Transverse duplex US image at the level of the origin of the IMA (arrowhead) demonstrates retrograde flow (the below-baseline component of the spectral waveform) into the aneurysm in the native aorta.
|
|
View larger version (205K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2b. Follow-up images obtained in the same patient as in Figure 1 after repair of the type I leak. (a) Transverse CT angiogram at the level of the origin of the small, patent, and enhancing IMA (open arrowhead). A recurrent small endoleak (solid arrowheads) appears as an area of faint contrast enhancement within the native aorta, anterior to the patent limbs of the stent-graft (arrows). (b) Conventional aortogram in an anterior oblique projection shows retrograde reconstitution of the IMA (open arrowhead) through the arc of Riolan; a focal, small collection of contrast material (solid arrowhead) is seen outside the graft and inside the aneurysm in the native aorta. (c) Transverse duplex US image shows a patent IMA (arrowheads) with a complex flow pattern on the spectral waveform. There is a short segment of early systolic antegrade flow (below baseline) followed by a dominant late systolic retrograde flow component (represented by an above-baseline component directed toward the transducer, but reversing to the direction of blood flow expected in a normal IMA). The early antegrade component may be related to transmitted pulsations from the endograft. The graft expands during systole and thus creates a propulsive effect on residual blood pooling in the native aorta adjacent to the graft. Once the collateral vessels fill the IMA in retrograde fashion in late systole, the dominant retrograde flow becomes apparent. The late retrograde component of the spectral waveform represents the endoleak flow entering back into the aorta. (d) Transverse duplex US image at the level of the origin of the IMA (arrowhead) demonstrates retrograde flow (the below-baseline component of the spectral waveform) into the aneurysm in the native aorta.
|
|
View larger version (99K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2c. Follow-up images obtained in the same patient as in Figure 1 after repair of the type I leak. (a) Transverse CT angiogram at the level of the origin of the small, patent, and enhancing IMA (open arrowhead). A recurrent small endoleak (solid arrowheads) appears as an area of faint contrast enhancement within the native aorta, anterior to the patent limbs of the stent-graft (arrows). (b) Conventional aortogram in an anterior oblique projection shows retrograde reconstitution of the IMA (open arrowhead) through the arc of Riolan; a focal, small collection of contrast material (solid arrowhead) is seen outside the graft and inside the aneurysm in the native aorta. (c) Transverse duplex US image shows a patent IMA (arrowheads) with a complex flow pattern on the spectral waveform. There is a short segment of early systolic antegrade flow (below baseline) followed by a dominant late systolic retrograde flow component (represented by an above-baseline component directed toward the transducer, but reversing to the direction of blood flow expected in a normal IMA). The early antegrade component may be related to transmitted pulsations from the endograft. The graft expands during systole and thus creates a propulsive effect on residual blood pooling in the native aorta adjacent to the graft. Once the collateral vessels fill the IMA in retrograde fashion in late systole, the dominant retrograde flow becomes apparent. The late retrograde component of the spectral waveform represents the endoleak flow entering back into the aorta. (d) Transverse duplex US image at the level of the origin of the IMA (arrowhead) demonstrates retrograde flow (the below-baseline component of the spectral waveform) into the aneurysm in the native aorta.
|
|
View larger version (97K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 2d. Follow-up images obtained in the same patient as in Figure 1 after repair of the type I leak. (a) Transverse CT angiogram at the level of the origin of the small, patent, and enhancing IMA (open arrowhead). A recurrent small endoleak (solid arrowheads) appears as an area of faint contrast enhancement within the native aorta, anterior to the patent limbs of the stent-graft (arrows). (b) Conventional aortogram in an anterior oblique projection shows retrograde reconstitution of the IMA (open arrowhead) through the arc of Riolan; a focal, small collection of contrast material (solid arrowhead) is seen outside the graft and inside the aneurysm in the native aorta. (c) Transverse duplex US image shows a patent IMA (arrowheads) with a complex flow pattern on the spectral waveform. There is a short segment of early systolic antegrade flow (below baseline) followed by a dominant late systolic retrograde flow component (represented by an above-baseline component directed toward the transducer, but reversing to the direction of blood flow expected in a normal IMA). The early antegrade component may be related to transmitted pulsations from the endograft. The graft expands during systole and thus creates a propulsive effect on residual blood pooling in the native aorta adjacent to the graft. Once the collateral vessels fill the IMA in retrograde fashion in late systole, the dominant retrograde flow becomes apparent. The late retrograde component of the spectral waveform represents the endoleak flow entering back into the aorta. (d) Transverse duplex US image at the level of the origin of the IMA (arrowhead) demonstrates retrograde flow (the below-baseline component of the spectral waveform) into the aneurysm in the native aorta.
|
|
A type II endoleak was diagnosed in a second patient at CT angiography (Fig 3a). Duplex US depicted antegrade flow within the IMA and a high-velocity retrograde flow pattern in the aneurysmal native right common iliac artery outside the iliac limb of the stent-graft (Fig 3b, 3c). The diagnosis of type I endoleak was suggested. Findings at urgent aortography confirmed the diagnosis at US, and repair with placement of a Wallgraft device was performed (Fig 3d). Repeat CT angiography revealed a small lumbar reconstitution leak posterior to the stent-graft limbs that had not been identified at duplex US.
View larger version (137K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3a. Images in a 78-year-old man with a bifurcated aortic stent-graft placed for treatment of an infrarenal AAA. (a) Transverse CT angiogram of the distal portion of the abdominal aorta demonstrates extravasation of contrast material (arrowhead) within the native aorta posterior to the patent limbs (arrows) of the stent-graft. The graft attachment sites (not shown) were normal. (b) Conventional aortogram with selective contrast material injection into the left iliac limb demonstrates double intensity of contrast enhancement. The thicker column of contrast material (arrows) outlines the graft. Lighter contrast intensity is seen outside the graft within the native common iliac artery; this finding confirms the presence of a type I leak (arrowheads). (c) Transverse US image in a superior angle along the left common iliac artery (arrowheads) with a Doppler gate (double lines) placed inside the distal iliac graft limb demonstrates normal antegrade flow (the above-baseline component in the spectral waveform) toward the transducer in the patent graft limb. (d) Transverse US image in a superior angle along the left common iliac artery (arrowheads); a Doppler gate (double lines) has been placed in the native iliac artery outside the distal iliac graft limb. Doppler tracing demonstrates abnormal retrograde flow (a below-baseline component) in the native vessel away from the transducer; this finding is suggestive of a type I attachment site leak. The flow component seen above baseline in this tracing represents artifact from the adjacent antegrade flow within the graft.
|
|
View larger version (144K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3b. Images in a 78-year-old man with a bifurcated aortic stent-graft placed for treatment of an infrarenal AAA. (a) Transverse CT angiogram of the distal portion of the abdominal aorta demonstrates extravasation of contrast material (arrowhead) within the native aorta posterior to the patent limbs (arrows) of the stent-graft. The graft attachment sites (not shown) were normal. (b) Conventional aortogram with selective contrast material injection into the left iliac limb demonstrates double intensity of contrast enhancement. The thicker column of contrast material (arrows) outlines the graft. Lighter contrast intensity is seen outside the graft within the native common iliac artery; this finding confirms the presence of a type I leak (arrowheads). (c) Transverse US image in a superior angle along the left common iliac artery (arrowheads) with a Doppler gate (double lines) placed inside the distal iliac graft limb demonstrates normal antegrade flow (the above-baseline component in the spectral waveform) toward the transducer in the patent graft limb. (d) Transverse US image in a superior angle along the left common iliac artery (arrowheads); a Doppler gate (double lines) has been placed in the native iliac artery outside the distal iliac graft limb. Doppler tracing demonstrates abnormal retrograde flow (a below-baseline component) in the native vessel away from the transducer; this finding is suggestive of a type I attachment site leak. The flow component seen above baseline in this tracing represents artifact from the adjacent antegrade flow within the graft.
|
|
View larger version (92K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3c. Images in a 78-year-old man with a bifurcated aortic stent-graft placed for treatment of an infrarenal AAA. (a) Transverse CT angiogram of the distal portion of the abdominal aorta demonstrates extravasation of contrast material (arrowhead) within the native aorta posterior to the patent limbs (arrows) of the stent-graft. The graft attachment sites (not shown) were normal. (b) Conventional aortogram with selective contrast material injection into the left iliac limb demonstrates double intensity of contrast enhancement. The thicker column of contrast material (arrows) outlines the graft. Lighter contrast intensity is seen outside the graft within the native common iliac artery; this finding confirms the presence of a type I leak (arrowheads). (c) Transverse US image in a superior angle along the left common iliac artery (arrowheads) with a Doppler gate (double lines) placed inside the distal iliac graft limb demonstrates normal antegrade flow (the above-baseline component in the spectral waveform) toward the transducer in the patent graft limb. (d) Transverse US image in a superior angle along the left common iliac artery (arrowheads); a Doppler gate (double lines) has been placed in the native iliac artery outside the distal iliac graft limb. Doppler tracing demonstrates abnormal retrograde flow (a below-baseline component) in the native vessel away from the transducer; this finding is suggestive of a type I attachment site leak. The flow component seen above baseline in this tracing represents artifact from the adjacent antegrade flow within the graft.
|
|
View larger version (100K):
[in this window]
[in a new window]
[Download PPT slide]
|
Figure 3d. Images in a 78-year-old man with a bifurcated aortic stent-graft placed for treatment of an infrarenal AAA. (a) Transverse CT angiogram of the distal portion of the abdominal aorta demonstrates extravasation of contrast material (arrowhead) within the native aorta posterior to the patent limbs (arrows) of the stent-graft. The graft attachment sites (not shown) were normal. (b) Conventional aortogram with selective contrast material injection into the left iliac limb demonstrates double intensity of contrast enhancement. The thicker column of contrast material (arrows) outlines the graft. Lighter contrast intensity is seen outside the graft within the native common iliac artery; this finding confirms the presence of a type I leak (arrowheads). (c) Transverse US image in a superior angle along the left common iliac artery (arrowheads) with a Doppler gate (double lines) placed inside the distal iliac graft limb demonstrates normal antegrade flow (the above-baseline component in the spectral waveform) toward the transducer in the patent graft limb. (d) Transverse US image in a superior angle along the left common iliac artery (arrowheads); a Doppler gate (double lines) has been placed in the native iliac artery outside the distal iliac graft limb. Doppler tracing demonstrates abnormal retrograde flow (a below-baseline component) in the native vessel away from the transducer; this finding is suggestive of a type I attachment site leak. The flow component seen above baseline in this tracing represents artifact from the adjacent antegrade flow within the graft.
|
|
|
Discussion
|
|---|
Endovascular treatment of AAAs with stent-grafts has become a well-established alternative to open surgical repair in a population of selected patients (4,5). Although these procedures are effective in terms of short-term outcome, long-term implications remain unknown (17). Endoleaks are one of the most common problems occurring after stent-graft repair of AAAs, with reported rates up to 47% (7,18). Previous studies have shown that an AAA repaired with a stent-graft may continue to increase in size when an endoleak is present (19–23). The risk of aortic rupture after repair with an endostent is multifactorial and depends on the size and type of leak (24). Reliable diagnosis of an endoleak and its source is therefore essential in determining appropriate treatment. Patients with attachment-site (type I) endoleaks generally require urgent endovascular repair. Reconstitution (type II) leaks, especially small reconstitution leaks, are often treated conservatively because of their tendency to resolve spontaneously (7,9). Our study demonstrates that use of duplex US may alter patient care by revealing the true origin of type I attachment-site leaks that simulate type II reconstitution leaks at CT angiography.
CT angiography and duplex US are both used in the follow-up of patients treated with endovascular stent-graft placement for repair of an AAA (10,11). These techniques offer similarly high sensitivity and specificity for identifying the presence of endoleaks (9,12). Conventional aortography is not commonly used for initial postoperative follow-up in patients with aortic stent-grafts because of its relatively low sensitivity (63%) and specificity (77%) compared with those of CT angiography (25). Aortography is typically reserved for patients requiring further evaluation of vascular anatomy and/or complications from endoluminal repair of complications arising from stent-graft placement. In the United States, CT angiography has been more readily accepted and is more frequently used as the imaging modality of choice in routine follow-up examinations after stent-graft repair.
Several researchers have demonstrated that the reliability of duplex US is comparable to that of CT angiography for depiction of endoleaks in AAAs repaired with stent-grafts (10–12). Wolf et al (10) reported a sensitivity of 81% and a specificity of 95% for duplex US when duplex US results were compared with CT angiographic results. D’Audiffret et al (11) described a sensitivity of 96% and a specificity of 94% for duplex US when duplex US results were compared with CT angiographic results. This group also demonstrated the feasibility of using duplex US in the differentiation of various types of endoleaks. Although the results of the present study appear to demonstrate a greater degree of discrepancy between CT angiographic and duplex US findings, there is a fundamental difference between the approach of our study and the approaches of those previously cited. Our study was limited to patients with endoleaks seen at CT angiography. In our study, duplex US was performed after CT angiography to enable assessment of the possible added benefit of duplex US. In addition to using it to help confirm the presence of an endoleak identified at CT angiography, we used duplex US to determine the mechanism, size, and origin of the endoleak; this information guided subsequent management. Finally, CT angiographic results were not treated as the standard of reference in our study.
In addition to enabling visualization of an endoleak, duplex US provides information about the direction and velocity of flowing blood. Type I attachment-site leaks are characterized by the same kind of high velocity of blood flow at the site of the leak that one might observe at the site of an arterial stenosis. Distal attachment-site leaks are characterized by a reversal of blood flow outside the graft lumen but normal flow direction in the distal portion of the graft. In the setting of a type I leak, antegrade flow may be documented in a patent IMA. Type II reconstitution leaks are characterized by a low velocity of blood flow. When reconstitution occurs through the IMA, a patent IMA with reversal of flow toward the aorta is identified. Patent lumbar arteries are difficult to visualize due to their size and posterior location. However, the endoleak can often be traced to its origin at the native aortic wall, and blood flow direction into the aorta can be confirmed.
Potential limitations of duplex US are related to the possibility of bowel gas obscuring the region of the aorta and the endograft in the abdomen. The likelihood that this problem will occur can be reduced by instructing the patient to fast for at least 6 hours before the examination. US is operator dependent and time consuming, and an experienced sonographer and state-of-the-art equipment are required for the modality to achieve optimal diagnostic utility. The location of an endoleak and the presence of slowly flowing blood and/or extensive atherosclerotic calcification or metallic hardware in the field of view of the transducer may limit visualization of small leaks. The single endoleak not demonstrated at duplex US in our series was a very small lumbar reconstitution leak seen at CT angiography in the distal portion of the AAA, posterior to the two limbs of a Wallstent-repaired stent-graft. Thus, the additional hardware associated with the leak, as well as the location of the leak, may have prevented its visualization with duplex US.
The physiologic flow information provided by duplex US is complementary to the anatomic information provided by CT angiography. CT angiography may be more useful as a screening tool for endoleaks. However, patients who are found to have an endoleak at CT angiography should be examined with duplex US to enable further assessment of the type of the leak and to facilitate appropriate treatment. Although the conclusions drawn in this study are based on results in a small number of patients, these results had substantial consequences for the treatment of the patients in our study population.
|
Conclusions
|
|---|
Previous researchers have evaluated the ability of CT angiography and US to depict endograft leaks (10,11). CT angiography and state-of-the-art duplex US are of comparable utility in the assessment of aneurysm size and graft patency and the detection of endoleaks. Our preliminary data demonstrate that complementary use of CT angiography and duplex US can enable detection and characterization of endoleaks by resulting in acquisition of both anatomic information and hemodynamic flow information.
|
FOOTNOTES
|
|---|
Abbreviations: AAA = abdominal aortic aneurysm,
IMA = inferior mesenteric artery
Author contributions: Guarantor of integrity of entire study, A.L.G.; study concepts and design, A.L.G., E.J.H.; literature research, A.L.G., J.B.; clinical studies, all authors; data acquisition and analysis/interpretation, all authors; manuscript preparation, definition of intellectual content, editing, revision/review, and final version approval, all authors.
|
REFERENCES
|
|---|
- Parodi JC, Palmaz JC, Barone HD. Transfemoral intraluminal graft implantation for abdominal aortic aneurysms. Ann Vasc Surg 1991; 5:491-499.[CrossRef][Medline]
- Nasim A, Thompson MM, Sayers RD, et al. Endovascular repair of abdominal aortic aneurysm: an initial experience. Br J Surg 1996; 83:516-519.[Medline]
- White GH, Yu W, May J, et al. Three-year experience with the White-Yu endovascular GAD graft for transluminal repair of aortic and iliac aneurysms. J Endovasc Surg 1997; 4:124-136.[CrossRef][Medline]
- Kaufman JA, Geller SC, Brewster DC, et al. Endovascular repair of abdominal aortic aneurysms: current status and future directions. AJR Am J Roentgenol 2000; 175:289-302.[Free Full Text]
- Murphy KD, Richter GM, Henry M, et al. Aortoiliac aneurysms: management with endovascular stent-graft placement. Radiology 1996; 198:473-480.[Abstract/Free Full Text]
- Ahn S, Rutherford R, Johnston K, et al. Reporting standards for infrarenal endovascular abdominal aortic aneurysm repair. J Vasc Surg 1997; 25:405-410.[CrossRef][Medline]
- White GH, Yu W, May J, et al. Endoleak as a complication of endoluminal grafting of abdominal aortic aneurysms: classification, incidence, diagnosis, and management. J Endovasc Surg 1997; 4:152-168.[CrossRef][Medline]
- White GH, May J, Waugh RC, et al. Type III and Type IV endoleak: toward a complete definition of blood flow in the sac after endoluminal AAA repair. J Endovasc Surg 1998; 5:305-309.[CrossRef][Medline]
- Heilberger P, Schunn C, Ritter W, et al. Postoperative color flow duplex scanning in aortic endografting. J Endovasc Surg 1997; 4:262-271.[CrossRef][Medline]
- Wolf YG, Johnson BL, Hill BB, et al. Duplex ultrasound scanning versus computed tomographic angiography for postoperative evaluation of endovascular abdominal aortic aneurysm repair. J Vasc Surg 2000; 32:1142-1148.[CrossRef][Medline]
- D’Audiffret A, Desgranges P, Kobeiter DH, et al. Follow-up evaluation of endoluminally treated abdominal aortic aneurysms with duplex ultrasonography: validation with computed tomography. J Vasc Surg 2001; 33:42-50.[CrossRef][Medline]
- Sato DT, Goff CD, Gregory RT, et al. Endoleak after aortic stent graft repair: diagnosis by color duplex ultrasound scan versus computed tomography scan. J Vasc Surg 1998; 28:657-663.[CrossRef][Medline]
- Balm R, Jacobs MJ. Use of spiral computed tomographic angiography in monitoring abdominal aortic aneurysms after transfemoral endovascular repair. Tex Heart Inst J 1997; 24:200-203.[Medline]
- Fillinger MF. Postoperative imaging after endovascular AAA repair. Semin Vasc Surg 1997; 13:149-153.
- Rozenblit A, Marin M, Veith F, et al. Endovascular repair of abdominal aortic aneurysm: value of postoperative follow-up with helical CT. AJR Am J Roentgenol 1995; 165:1473-1479.[Abstract/Free Full Text]
- Rydberg J, Kopecky KK, Johnson MS, et al. Endovascular repair of abdominal aortic aneurysms: assessment with multislice CT. AJR Am J Roentgenol 2001; 177:607-614.[Free Full Text]
- Chuter TAM, Gordon RL, Reilly LM, et al. Abdominal aortic aneurysm in high-risk patients: short- to intermediate-term results of endovascular repair. Radiology 1999; 210:361-365.[Abstract/Free Full Text]
- Matsumura JS, Moore WS. Clinical consequences of periprosthetic leak after endovascular repair of abdominal aortic aneurysm. Endovascular Technologies Investigators. J Vasc Surg 1998; 27:606- 613.
- Matsumura JS, Chaikof EL. Anatomic changes after endovascular grafting for aneurysmal disease. Semin Vasc Surg 1999; 12:192-198.[Medline]
- Jacobowitz GR, Rosen RJ, Riles TS. The significance and management of the leaking endograft. Semin Vasc Surg 1999; 12:199-206.[Medline]
- Broeders IA, Blankensteijn JD, Gvakharia A, et al. The efficacy of transfemoral endovascular aneurysm management: a study on size changes of the abdominal aorta during mid-term follow-up. Eur J Vasc Endovasc Surg 1997; 14:89-90.
- Matsumura JS, Pearce WH. Preexisting thrombus and aortic aneurysm size change after endovascular repair. J Surg Res 1999; 81:11-14.[CrossRef][Medline]
- May J, White GH, Yu W, et al. A prospective study of changes in morphology and dimension of abdominal aortic aneurysms following endoluminal repair: a preliminary report. J Endovasc Surg 1995; 2:343-347.[CrossRef][Medline]
- Wain RA, Marin ML, Ohki T, et al. Endoleaks after endovascular graft treatment of aortic aneurysms: classification, risk factors, and outcome. J Vasc Surg 1998; 27:69-80.[CrossRef][Medline]
- Armerding MD, Rubin GD, Beaulieu CF, et al. Aortic aneurysmal disease: assessment of stent-graft treatment—CT versus conventional angiography. Radiology 2000; 215:138-146.[Abstract/Free Full Text]
This article has been cited by other articles:
|
|
|
|
 
S. W. Stavropoulos and S. R. Charagundla
Imaging Techniques for Detection and Management of Endoleaks after Endovascular Aortic Aneurysm Repair
Radiology,
June 1, 2007;
243(3):
641 - 655.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
V. Napoli, I. Bargellini, S. G. Sardella, P. Petruzzi, R. Cioni, C. Vignali, M. Ferrari, and C. Bartolozzi
Abdominal Aortic Aneurysm: Contrast-enhanced US for Missed Endoleaks after Endoluminal Repair
Radiology,
October 1, 2004;
233(1):
217 - 225.
[Abstract]
[Full Text]
[PDF]
|
|
|
TOP
ABSTRACT
INTRODUCTION
