(Radiographics. 1999;19:1573-1583.)
© RSNA, 1999
Helical CT Angiography of Stent-Grafts in Abdominal Aortic Aneurysms: Morphologic Changes and Complications1
Manfred Tillich, MD ,
Klaus A. Hausegger, MD ,
Kurt Tiesenhausen, MD ,
Josef Tauss, MD ,
Reinhard Groell, MD and
Dieter H. Szolar, MD
1 From the Departments of Radiology (M.T., K.A.H., J.T., R.G., D.H.S.) and Vascular Surgery (K.T.), Karl-Franzens Medical School and University Hospital, Graz, Austria. Presented as a scientific exhibit at the 1998 RSNA scientific assembly. Received March 30, 1999; revision requested April 20 and received June 9; accepted June 9. Address reprint requests to M.T., Department of Radiology, Section of Thoracic Imaging, Stanford University Medical Center, 300 Pasteur Dr, Stanford, CA 94305-5105.
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Abstract
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Transfemoral placement of an endovascular stent-graft is increasingly being used as an alternative to surgical repair in the treatment of abdominal aortic aneurysm, especially in high-risk patients. However, complications frequently occur after stent-graft placement. Helical computed tomographic (CT) angiography is a fast, minimally invasive procedure that is quickly becoming the imaging modality of choice for assessment of these complications. Thirty-nine patients who were treated for abdominal aortic aneurysm with stent-graft placement underwent helical CT angiography at routinely scheduled follow-up intervals or whenever complications were suspected. The resulting images were evaluated for the presence, extent, and origin of endovascular leaks. In addition, the position, shape, and patency of the stent-grafts were assessed. Findings included both graft-related (n = 4) and non–graft-related (n = 3) leaks, thrombosis of a graft limb (n = 3), distal migration of the stent-graft (n = 5), angulation of bifurcated stent-grafts distal to the main graft (n = 6), shrinkage of the abdominal aortic aneurysm (n = 7), enlargement of the aneurysm with secondary graft-related leaks (n = 2), and an aortoduodenal fistula (n = 1). Helical CT angiography can depict complications that develop after treatment of abdominal aortic aneurysms with endovascular stent-grafts. Long-term follow-up is required to determine the full spectrum and frequency of complications that may develop after initially successful repair.
Index Terms: Aneurysm, aortic, 981.73 • Aneurysm, CT, 981.12915, 981.12916 • Aneurysm, therapy, 981.1268 • Computed tomography, angiography, 981.12915, 981.12916 • Stents and prostheses, 981.1268
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INTRODUCTION
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The current standard of treatment for abdominal aortic aneurysm is open surgical repair, which is associated with a low overall risk. The reported mortality rate associated with elective surgical repair ranges from 1.4% to 6.5% (1). However, in high-risk patients with a comorbid medical condition such as severe cardiovascular, pulmonary, or renal disease, the risk of death during surgical repair of abdominal aortic aneurysm is considerably higher (5.7%–31%) (2). In an attempt to reduce risk in these patients, less invasive methods of repair have been considered. Treatment of abdominal aortic aneurysm with transfemoral placement of an endovascular stent-graft is increasingly being used as an alternative to surgical repair (3,4). However, complications related to the procedure such as graft limb thrombosis, peripheral embolization, and local hematoma have been reported (1,3,4). Furthermore, leaks have been associated with incomplete exclusion of the aneurysm sac (1,3–5).
In 1969, Dotter (6) introduced the concept of an intraluminally placed stent-graft. Many feasibility studies of different stent concepts for endoluminal grafting were conducted in animals before covered endovascular stent-grafts were implanted in humans (7–10). In 1991, Parodi et al (11) reported the transfemoral placement of nonbifurcated stent-grafts for treatment of abdominal aortic aneurysms in a series of human patients. However, this series was limited to patients with abdominal aortic aneurysm that did not involve the bifurcation and iliac arteries. In 1994, Scott and Chuter (12) successfully placed a bifurcated stent-graft designed by Chuter et al (10) in six patients with abdominal aortic aneurysms.
Although conventional arteriography has long been considered the modality of choice for arterial imaging, there are several reasons why helical computed tomographic (CT) angiography may be superior in the assessment of the abdominal arteries. First, the acquisition of volumetric data with helical CT allows clear delineation of the tortuous aorta and branch vessels and of adjacent aneurysms and pseudoaneurysms. Because conventional angiography is a projectional imaging technique, the overlap of these structures can make their visualization difficult. Second, blood pool imaging with the intravenous administration of contrast material allows visualization of true and false luminal flow channels, intramural hematomas communicating with the aortic lumen, and slow perigraft flow around aortic stent-grafts. Finally, the aortic wall and noncommunicating intramural collections can be directly visualized with CT angiography. These advantages, together with the fast, minimally invasive nature of this procedure, have resulted in CT angiography replacing conventional angiography as the primary imaging modality for many applications in the abdomen (13). Several studies have shown that helical CT is the most sensitive imaging technique for evaluation of the results of endoluminal stent-graft therapy (5,14).
Recent advances in magnetic resonance (MR) imaging technology have substantially improved the quality of abdominal MR angiography (15,16). Although MR angiography has potential for assessing the postoperative vasculature, metallic clips or stent-grafts can produce considerable magnetic susceptibility artifacts. In contrast, most stent-grafts cause minimal artifact at CT angiography, giving this technique a substantial advantage over MR imaging (17).
In this article, we demonstrate the accuracy of helical CT angiography in depicting postprocedural complications in abdominal aortic aneurysms treated with endoluminal placement of stent-grafts. In addition, we discuss and illustrate morphologic changes in stent-grafts that may affect the success of endoluminal stent-graft placement during long-term follow-up.
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MATERIALS AND METHODS
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Patient Population
Abdominal aortic aneurysm was treated in 39 patients (37 men and two women; age range, 51–81 years [mean, 67 years]) with an endovascular nitinol-polyester stent-graft (Vanguard; Boston Scientific, Oakland, NJ) (Fig 1). A tube was used in six patients, and a bifurcated graft was used in 33.
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Figure 1a. Basic designs of nitinol stents covered with woven Dacron (polyethylene terephthalate fiber) graft material. (a) Photograph shows a tube stent-graft. The stent frame is covered with a thin-woven polyester fabric. The leading part of the stent-graft is uncovered (arrows). (b) Photograph shows a bifurcated stent-graft. The device has two components, which are inserted separately and mated in place: The main graft has a single limb, and a second limb is inserted contralaterally and implanted in the trailing end of the main graft (arrows).
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Figure 1b. Basic designs of nitinol stents covered with woven Dacron (polyethylene terephthalate fiber) graft material. (a) Photograph shows a tube stent-graft. The stent frame is covered with a thin-woven polyester fabric. The leading part of the stent-graft is uncovered (arrows). (b) Photograph shows a bifurcated stent-graft. The device has two components, which are inserted separately and mated in place: The main graft has a single limb, and a second limb is inserted contralaterally and implanted in the trailing end of the main graft (arrows).
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The stent-graft was inserted via a femoral arteriotomy opening over an extraordinarily stiff guide wire (Schneider, Buelach, Switzerland) within an 18-F introducer sheath. For bifurcated grafts, the opposite femoral artery was punctured and the opposite iliac stent branch was inserted through a 10-F introducer sheath.
Postoperative Follow-up
Follow-up protocol included helical CT angiography at 1 week and at 1 month, 3 months, and every 3 months thereafter or whenever complications were suspected. Duration of follow-up in patients with aortic stent-grafts ranged from 1 week to 24 months (mean, 8.8 months).
Imaging Technique
Helical CT was performed with a Somatom Plus 4 scanner (Siemens, Erlangen, Germany) with a maximum continuous scanning time of 50 seconds. To define the imaging volume of interest, unenhanced CT scans (8-mm collimation, 1.5:1 pitch) were obtained from the level of the diaphragm level to the symphysis pubis. An 18- to 20-gauge antecubital intravenous catheter was subsequently positioned and flushed vigorously with saline solution to ensure that it could safely allow an adequate infusion rate.
A test bolus of 20 mL of nonionic iopromide (Ultravist 370; Schering, Berlin, Germany) was injected at a rate of 4 mL/sec. Beginning 10 seconds after initiation of the test injection, single-level dynamic CT scans were obtained every 2 seconds at the level of the renal arteries. A total of 15 scans were obtained, and a region of interest was located at the abdominal aorta, resulting in a time-attenuation curve that was then used to determine an appropriate delay time between initiation of the injection and start of the imaging sequence. The interval between start of the injection and maximum contrast enhancement of the aorta was selected as the delay time.
Before helical CT was begun, the patients practiced breath holding to minimize motion artifacts. The patients were instructed to begin quiet ventilation after a total of 30 seconds of breath holding had been achieved. By this time, the scanner was invariably being used to image within the pelvis, where respiratory misregistration was not substantial.
For the contrast-enhanced sequence, a 120-mL bolus of iopromide was injected with an automatic power injector (Medrad, Pittsburgh, Pa) at a rate of 4 mL/sec and CT scans (3-mm collimation, 1.5:1 pitch) were obtained from the celiac origin to the bifurcations of the femoral arteries. The highest milliamperage level that the tube heat limit would permit (mean, 295 mA) was used. The data were prospectively reconstructed at 2-mm intervals. Images were sent via ethernet to a CT workstation (Sienet Magic View, Siemens), where maximum-intensity-projection and shaded-surface display images were produced with standard software.
CT Angiographic Evaluation
The CT angiograms were interpreted by one of five faculty radiologists (M.T., K.A.H., J.T., R.G., D.H.S.) on the workstation. Evaluation of the reconstructed axial images was performed in cine mode. Findings on the three-dimensional reconstructed images were correlated with those on the axial source images.
The axial helical CT scans were evaluated for the presence, extent, and origin of leaks. Leakage was defined as the persistence of blood flow outside the lumen of the endoluminal graft but within the aneurysm sac (18). Leaks were categorized according to when they developed, so that all leakage that occurred during the perioperative period (ie, within 30 days after surgery) was defined as primary endovascular leakage. Endovascular leakage that occurred as a late event after successful stent-graft implantation was defined as secondary endovascular leakage. A distinction was also made between leakage related to the stent-graft (graft-related leakage) and leakage associated with retrograde flow from collateral arterial branches (non–graft-related leakage) (18). A non–graft-related leak was defined as extravasation of contrast material into the periphery of the aneurysm sac caused by retrograde perfusion of patent collateral arteries. Furthermore, the position, shape, and patency of the stent-graft were assessed with the axial CT scans and the three-dimensional reconstructed images.
Correlation of Surgical and CT Angiographic Findings
Surgery was performed in two patients by an experienced vascular surgeon (K.T.) who had prior knowledge of the imaging findings. Surgical findings were recorded in the operating room and later correlated with CT angiographic findings.
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RESULTS
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A primary non–graft-related leak caused by persistent blood flow into the aneurysm sac was seen in three of 39 patients immediately after therapy. All non–graft-related leaks occurred in the periphery of the aneurysm sac. The leak was caused by flow from a patent inferior mesenteric artery in one patient (Fig 2) and by flow from patent lumbar arteries in two patients (Fig 3). Helical CT adequately depicted the supplying vessels in all three patients. A primary graft-related distal leak occurred in one of 33 patients with a bifurcated graft (Figs 4, 5). A secondary graft-related leak was seen in two of 33 patients with a bifurcated graft and in one of six patients with a tube graft 9–18 months after therapy (Figs 6–8). Distal migration of the proximal portion of the stent-graft without leakage was seen in two of the six patients with a tube graft and in four of the 33 patients with a bifurcated graft 6–24 months after therapy (Fig 9). Angulation of bifurcated grafts distal to the main graft was observed in six of 33 patients 3–18 months after therapy, and angulation was associated with distal migration of the proximal portion of the stent-graft in three patients (Fig 10). Complete thrombosis of a graft limb was seen in three of 33 patients with bifurcated grafts 1 week to 5 months after therapy. In one of these three patients, a crescent-shaped, parietal thrombus within the main graft was seen extending distally into the left graft limb (Fig 11). The patient underwent open surgery because thrombolysis failed to reopen the vessel. The stent-graft was removed, and surgical repair of the abdominal aortic aneurysm was performed.
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Figure 2. Primary non-graft-related leak after therapy with a bifurcated graft. Axial helical CT scan obtained 1 week after therapy shows a primary non-graft-related leak (arrow) caused by collateral flow into the aneurysm sac from a patent inferior mesenteric artery (arrowheads).
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Figure 3. Primary non-graft-related leak after therapy with a bifurcated graft. Axial helical CT scan obtained 1 week after therapy shows a primary non-graft-related leak (arrows) caused by persistent flow into the aneurysm sac from patent lumbar arteries (arrowheads).
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Figure 4a. Primary graft-related leak after therapy with a bifurcated graft. (a) Axial helical CT scan obtained 1 week after therapy shows a primary graft-related leak at the medial distal aspect of the left graft limb (arrowheads). (b) Axial helical CT scan obtained at the proximal aspect of the graft limbs shows the leak anterior to the limbs (arrows). (c) Sagittal maximum intensity projection (MIP) image shows proximal extension of the leak (arrows).
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Figure 4b. Primary graft-related leak after therapy with a bifurcated graft. (a) Axial helical CT scan obtained 1 week after therapy shows a primary graft-related leak at the medial distal aspect of the left graft limb (arrowheads). (b) Axial helical CT scan obtained at the proximal aspect of the graft limbs shows the leak anterior to the limbs (arrows). (c) Sagittal maximum intensity projection (MIP) image shows proximal extension of the leak (arrows).
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Figure 4c. Primary graft-related leak after therapy with a bifurcated graft. (a) Axial helical CT scan obtained 1 week after therapy shows a primary graft-related leak at the medial distal aspect of the left graft limb (arrowheads). (b) Axial helical CT scan obtained at the proximal aspect of the graft limbs shows the leak anterior to the limbs (arrows). (c) Sagittal maximum intensity projection (MIP) image shows proximal extension of the leak (arrows).
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Figure 5a. Primary graft-related leak after therapy with a bifurcated graft. (a) Axial helical CT scan obtained 1 week after therapy shows a primary graft-related leak (arrow) caused by an incomplete seal at the junction of the main graft and the secondary implanted limb (arrowheads). (b) Axial helical CT scan obtained at the level of the graft limbs shows a leak in the posterior aspect of the aneurysm sac (arrows).
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Figure 5b. Primary graft-related leak after therapy with a bifurcated graft. (a) Axial helical CT scan obtained 1 week after therapy shows a primary graft-related leak (arrow) caused by an incomplete seal at the junction of the main graft and the secondary implanted limb (arrowheads). (b) Axial helical CT scan obtained at the level of the graft limbs shows a leak in the posterior aspect of the aneurysm sac (arrows).
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Figure 6. Secondary graft-related leak after therapy with a bifurcated graft. Axial helical CT scan obtained 12 months after therapy shows a secondary graft-related leak (arrowhead) at the junction of the main graft and the secondary implanted right limb (white arrow) caused by disconnection of the graft limb (black arrow).
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Figure 7a. Secondary graft-related leak after therapy with a bifurcated graft. (a) Axial helical CT scan obtained 18 months after therapy shows a secondary graft-related leak distal to the right graft limb (arrow). (b) Sagittal MIP image shows that the distal aspect of the right graft limb has migrated proximally into the aneurysm sac (arrow) and caused the leak.
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Figure 7b. Secondary graft-related leak after therapy with a bifurcated graft. (a) Axial helical CT scan obtained 18 months after therapy shows a secondary graft-related leak distal to the right graft limb (arrow). (b) Sagittal MIP image shows that the distal aspect of the right graft limb has migrated proximally into the aneurysm sac (arrow) and caused the leak.
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Figure 8a. Secondary graft-related leak after therapy with a tube graft. (a) Sagittal MIP image obtained 1 week after therapy shows a tube graft with normal position and shape. (b) Sagittal MIP image obtained 12 months after therapy shows a secondary graft-related leak at the anterior distal aspect of the tube graft. The distal wire-form attachment (arrow) has become detached from the aortic wall due to hemodynamic forces similar to those that may cause formation of an anastomotic aneurysm.
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Figure 8b. Secondary graft-related leak after therapy with a tube graft. (a) Sagittal MIP image obtained 1 week after therapy shows a tube graft with normal position and shape. (b) Sagittal MIP image obtained 12 months after therapy shows a secondary graft-related leak at the anterior distal aspect of the tube graft. The distal wire-form attachment (arrow) has become detached from the aortic wall due to hemodynamic forces similar to those that may cause formation of an anastomotic aneurysm.
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Figure 9a. Stent-graft migration after therapy with a bifurcated graft. (a) Coronal oblique MIP image obtained 1 week after therapy shows the proximal end of the graft below the origin of the right renal artery (arrow). (b) Coronal oblique MIP image obtained 18 months after therapy shows distal migration of the body of the bifurcated graft (arrow) and superior migration of the right graft limb without evidence of an endovascular leak.
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Figure 9b. Stent-graft migration after therapy with a bifurcated graft. (a) Coronal oblique MIP image obtained 1 week after therapy shows the proximal end of the graft below the origin of the right renal artery (arrow). (b) Coronal oblique MIP image obtained 18 months after therapy shows distal migration of the body of the bifurcated graft (arrow) and superior migration of the right graft limb without evidence of an endovascular leak.
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Figure 10a. Stent-graft angulation after therapy with a bifurcated graft. (a) Sagittal MIP image obtained 1 week after therapy shows a stent-graft with normal position and shape. (b) Sagittal MIP image obtained 12 months after therapy shows severe angulation of the stent-graft distal to the main graft and associated distal migration of the proximal end.
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Figure 10b. Stent-graft angulation after therapy with a bifurcated graft. (a) Sagittal MIP image obtained 1 week after therapy shows a stent-graft with normal position and shape. (b) Sagittal MIP image obtained 12 months after therapy shows severe angulation of the stent-graft distal to the main graft and associated distal migration of the proximal end.
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Figure 11a. Stent-graft thrombosis after therapy with a bifurcated graft. (a) Axial helical CT scan of the midgraft region obtained 5 months after therapy shows a crescent-shaped, parietal thrombus adjacent to the left wall of the stent-graft (arrowheads) extending distally into the left graft limb. (b) Photograph of the surgical specimen shows the thrombus adjacent to the left wall of the stent-graft (arrowheads). (c) Axial helical CT scan obtained at the level of the graft limbs shows complete thrombosis of the left graft limb (arrow).
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Figure 11b. Stent-graft thrombosis after therapy with a bifurcated graft. (a) Axial helical CT scan of the midgraft region obtained 5 months after therapy shows a crescent-shaped, parietal thrombus adjacent to the left wall of the stent-graft (arrowheads) extending distally into the left graft limb. (b) Photograph of the surgical specimen shows the thrombus adjacent to the left wall of the stent-graft (arrowheads). (c) Axial helical CT scan obtained at the level of the graft limbs shows complete thrombosis of the left graft limb (arrow).
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Figure 11c. Stent-graft thrombosis after therapy with a bifurcated graft. (a) Axial helical CT scan of the midgraft region obtained 5 months after therapy shows a crescent-shaped, parietal thrombus adjacent to the left wall of the stent-graft (arrowheads) extending distally into the left graft limb. (b) Photograph of the surgical specimen shows the thrombus adjacent to the left wall of the stent-graft (arrowheads). (c) Axial helical CT scan obtained at the level of the graft limbs shows complete thrombosis of the left graft limb (arrow).
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In another patient with a bifurcated graft, surgery was performed 21 months after therapy because a rupture at the proximal neck of the abdominal aortic aneurysm was suspected at helical CT (Fig 12). Surgery revealed fragmentation of the upper end of the stent-graft and an aortoduodenal fistula; these findings were not detected at CT.
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Figure 12a. Aortoduodenal fistula after therapy with a bifurcated graft. (a) Axial helical CT scan of the proximal graft region obtained 21 months after therapy shows deformity of the proximal end of the graft. The eccentric deformity of the aneurysm sac at the anterior lateral aspect cannot be distinguished from the posterior wall of the ascending part of the collapsed duodenum (arrows). (b) Intraoperative photograph taken during removal of the stent-graft reveals fragmentation of the proximal end of the stent-graft (arrows) and an aortoduodenal fistula. These findings were not detected at helical CT. (c) Photograph provides close-up view of the fragmented proximal end of the stent-graft.
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Figure 12b. Aortoduodenal fistula after therapy with a bifurcated graft. (a) Axial helical CT scan of the proximal graft region obtained 21 months after therapy shows deformity of the proximal end of the graft. The eccentric deformity of the aneurysm sac at the anterior lateral aspect cannot be distinguished from the posterior wall of the ascending part of the collapsed duodenum (arrows). (b) Intraoperative photograph taken during removal of the stent-graft reveals fragmentation of the proximal end of the stent-graft (arrows) and an aortoduodenal fistula. These findings were not detected at helical CT. (c) Photograph provides close-up view of the fragmented proximal end of the stent-graft.
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Figure 12c. Aortoduodenal fistula after therapy with a bifurcated graft. (a) Axial helical CT scan of the proximal graft region obtained 21 months after therapy shows deformity of the proximal end of the graft. The eccentric deformity of the aneurysm sac at the anterior lateral aspect cannot be distinguished from the posterior wall of the ascending part of the collapsed duodenum (arrows). (b) Intraoperative photograph taken during removal of the stent-graft reveals fragmentation of the proximal end of the stent-graft (arrows) and an aortoduodenal fistula. These findings were not detected at helical CT. (c) Photograph provides close-up view of the fragmented proximal end of the stent-graft.
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Shrinkage of the abdominal aortic aneurysm was observed in seven of 39 patients, and enlargement was seen in two of the three patients with secondary graft-related leaks.
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DISCUSSION
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Many investigators have reported the use of stent-grafts for the treatment of abdominal aortic aneurysms (3,4,19,20). These studies have shown that stent-graft therapy is a safe, effective procedure. However, growth and rupture of aneurysms have been reported in patients with persistent perigraft flow after stent-graft placement (21). The prevalence of reported leakage has ranged from approximately 10% or more in current practice to 44% with early devices (18). The severity of leakage is probably dependent on the size of the perigraft channel and the associated flow, so that small leaks may have less tendency to cause major complications. However, further research is required to determine which cases of leakage can be safely observed and which require early treatment because of the risk of aneurysm rupture.
Primary leaks (ie, those occurring during the 30-day perioperative period) may be caused by morphologic features of the aorta such as angulated proximal neck, short or noncircular attachment zones, and mural thrombus or severe calcifications within the attachment zones. Another possible cause may be misplacement of the stent-graft. Secondary leaks (ie, those occurring as late events after an initially complete seal) may be caused by the same factors that cause primary leakage. In addition, secondary leakage may arise from displacement of the proximal or distal end of the graft or from material fatigue and degradation over time.
Graft-related leakage has been attributed to an inadequate or ineffective seal at the graft ends or between segments of overlapping graft segments. Leakage at the midgraft region may be due to leakage through a defect in the polyester membrane of the graft. However, no membranous defect was found in any of the four patients in our study with distal graft-related leaks. Instead, these leaks were caused by graft limbs or tubes that were too short or that ended in the distal cone of the aortic aneurysm or by a size mismatch between the iliac graft limb and the vessel. In these patients, additional stents were implanted to seal the leaks. Dorffner et al (4) reported that leaks at the proximal end of the stent were most often caused by distal migration of the stent-graft. In our series, patients with distal stent-graft migration demonstrated no such leaks; nevertheless, limited follow-up may be necessary in such patients. In two patients, distal migration of the bifurcated graft caused proximal migration of the secondary graft limb, which was associated with a secondary graft-related distal leak in one patient (Fig 6).
Several studies have shown that non–graft-related leaks (ie, leaks attributed to retrograde perfusion of patent collateral arteries) have a greater tendency to seal by means of spontaneous thrombosis (unless there are two or more patent vessels), allowing flow both into and out of the aneurysm sac (5,18). In one patient, a leak caused by collateral flow from a patent inferior mesenteric artery persisted for 3 months, and transcatheter embolization of the leak was performed. Golzarian et al (22) recently reported that transcatheter embolization seems to be an effective and less invasive treatment for leaks associated with retrograde flow from collateral arterial branches of any origin that persist after 3 months. Nevertheless, the effect of postembolization thrombosis on aneurysmal growth must be validated with further investigation.
Rozenblit et al (5) reported that the most important variable in determining the efficacy of stent-graft placement for aortic abdominal aneurysm is most likely an interval change in the size of the aneurysm. Shrinkage of the excluded aneurysm may be attributed to clot retraction, whereas any enlargement of the aneurysm after treatment indicates failure of the procedure. Both shrinkage (n = 7) and enlargement (n = 2) were observed in our study.
Angulation of bifurcated grafts was observed in nine patients in our study. Significant angulation of a bifurcated graft may lead to stenosis or thrombosis at the junction of the main graft and the graft limbs or disconnection of the secondary inserted graft limb.
MIP images are particularly useful for depicting small vessels and the precise intravascular position and configuration of the stent-graft. However, they do not allow visualization of portions of vessels that are obscured by calcified plaque or by the high-attenuation stent-graft (5). Thus, evaluation of thrombi, emboli, or dissections is difficult with MIP technique. Shaded-surface display has limited value for assessment of endoluminal grafts because the stent-graft and intraluminal contrast material enhancement cannot be distinguished on the final display image.
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CONCLUSIONS
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Helical CT angiography is a fast, safe, minimally invasive imaging technique and as such is the modality of choice for the follow-up of patients who have undergone endovascular treatment for abdominal aortic aneurysm. Use of MIP technique often clarifies the complex anatomy of the tortuous aorta and branch vessels by showing the precise intravascular position and configuration of the stent-graft; however, flow of contrast material is at least partially obscured by the high-attenuation stent-graft. Axial source images accurately demonstrate leaks and the patency of the stent-graft. Long-term follow-up is necessary to determine the full spectrum and frequency of complications that may develop after initially successful stent-graft repair of an abdominal aortic aneurysm.
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Footnotes
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Abbreviation: MIP = maximum intensity projection
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References
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Abstract
INTRODUCTION
