| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
|
|
|
|||||||
|
|||||||||
1
Department of Radiology, Erasme Hospital, University of Brussels, 808 Route de
Lennik, 1070 Brussels, Belgium.
2
Department of Vascular Pathology, Erasme Hospital, University of Brussels,
1070 Brussels, Belgium.
Received December 29, 2000;
accepted after revision August 30, 2001.
Address correspondence to J. Golzarian.
Abstract
 Top Abstract IntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
MATERIALS AND METHODS. Fifty-five patients prospectively underwent both color Doppler sonography and helical CT within 7 days after treatment by endovascular stent-graft. Aneurysmal thrombosis, the patency of the grafts, and the presence of a leak were evaluated in all patients. When a perigraft leak was observed, an attempt was made to identify its origin and outflow vessels. Helical CT was considered the gold standard technique.
RESULTS. Helical CT revealed aneurysmal thrombosis in 33 patients and a perigraft leak in 22 patients. In five patients, helical CT detected a small perigraft leak not shown by color Doppler sonography. In three patients with suboptimal examinations, color Doppler sonography revealed a suspected perigraft leak that was not confirmed by helical CT. In these eight patients, the perigraft leak was sealed or no longer observed during follow-up. Compared with enhanced helical CT, the sensitivity and specificity of color Doppler sonography for the diagnosis of a perigraft leak were 77% and 90%, respectively. In seven other patients, helical CT was superior to color Doppler sonography in detecting the origin of the perigraft leak and the outflow vessels. Two iliac artery dissections and one distal migration of the prosthesis were revealed only by helical CT.
CONCLUSION. Although color Doppler sonography may detect substantial perigraft leaks, helical CT is superior for detecting the origin of the perigraft leak, the outflow vessels, and the detection of complications related to the procedure.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Contrast-enhanced helical CT is considered to be the primary imaging modality for the evaluation of the aorta after endoluminal repair [4, 8, 10, 12, 14]. Color Doppler sonography is highly dependent on operators and is limited in patients who are obese or have excessive bowel gas. Nevertheless, color Doppler sonography could be an ideal imaging technique because it is less expensive, widely available, and does not require iodine contrast medium injection or radiation. Several articles [3, 5, 15,16,17,18,19,20] report that CT and color Doppler sonography have been used during follow-up after endoluminal aortic repair. However, the accuracy of color Doppler sonography remains controversial.
The aim of this study is thus to compare color Doppler sonography with helical CT, considered the gold standard technique, in the surveillance of abdominal aortic aneurysms after endoluminal repair.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
The endoluminal graft is a fully metallic double-helix self-expandable stent, covered on its inner face by a coating of polycarbonate urethane. The stent is composed of 24-96 wires and is 0.01-0.23 mm in diameter. The diameter of the fibers that compose the stent coating range from 10 to 20 µm, and the interfiber distance measures 20-50 µm. The size of the delivery system for the main trunk is 18-French and for the iliac limbs, 12-French in diameter. The stent-graft procedure was performed by a surgeon, and the patients underwent general anesthesia with endobronchial intubation and mechanical ventilation.
Eight aortic tubes, 40 aortomonoiliac stent-grafts with an occlusive device (blinded stent-graft) in the contralateral iliac artery and the femoral-to-femoral bypass, and seven bifurcated stent-grafts were used for the stent-graft procedures.
All patients prospectively underwent color Doppler sonography and biphasic helical CT within 7 days after stent-graft implantation. The maximum time interval between helical CT and color Doppler sonography was 48 hr (mean, 11.5 hr); however, 33 patients had both examinations on the same day. In all patients, color Doppler sonography was performed before helical CT.
Color Doppler sonography and CT angiography were used as follow-up modalities in patients at 3, 6, and 12 months and every 6 months thereafter. Angiography was performed in cases of persistent leak to plan the optimal treatment. CT angiography started with a global injection of the aorta. Acquisition time was long enough to allow the detection of a type II endoleak. In case of a type I endoleak, the origin of the sac was catheterized and an intraaneurysmal injection was performed for optimal evaluation of the outflow vessels. The superior mesenteric artery and each of the internal iliac arteries were injected with contrast material to detect retrograde filling of the aneurysm from the inferior mesenteric artery or the iliolumbar arteries.
Color Doppler Sonography
Color Doppler sonography was performed by two experienced operators (one
angiologist and one radiologist) using a SSH-140A (Toshiba, Antwerpen,
Belgium) with a 2.5- and 3.75-MHz curved array transducer. Each patient was
evaluated by one physician. Patients were studied in the supine and lateral
positions after an overnight fast. The aorta was first scanned transversally
from the top of the stent-graft to the femoral arteries, and the maximal
transversal diameter was measured. Color Doppler imaging was then performed in
both the transverse and longitudinal axes. A leak was considered present when
a signal associated with a spectral Doppler signal was observed outside the
aorta. In case of a perigraft leak, an attempt was made to identify the origin
and the direction of the flow. Operators were unaware of the helical CT
results. The examination ranged from 15 to 30 min.
Helical CT
All helical CT examinations were performed by two experienced radiologists
on a Somatom Plus S or a 4A scanner (Siemens Medical Systems, Erlangen,
Germany). Either a bolus test injection of 15 mL of contrast medium or a bolus
tracking system with a threshold of 100 H was used to determine the optimal
start delay. Unenhanced CT scans were not obtained in our patients. The aorta
and iliac arteries were imaged from the celiac trunk to the common femoral
arteries using the following parameters: a collimation of 5 mm with a pitch of
1.2, 120 kV, and 240 mA. Patients received 80-120 mL of contrast medium at a
rate of 3.5 mL/sec. The contrast volume was calculated to deliver the bolus in
a time period equivalent to the scan duration. Fifteen seconds after the end
of the arterial phase acquisition, a delayed acquisition was performed using
the same parameters as the arterial phase and covering the stented volume. The
scan duration varied from 20 to 35 sec. All the images were reconstructed with
a 4-mm increment. A leak was considered present if contrast material was noted
outside the stent-graft in either acquisition. All images were reviewed on
radiographs and a workstation in conference with two radiologists who were
unaware of the color Doppler sonographic results. In this study, biphasic
helical CT was considered the gold standard. The examination ranged from 15 to
20 min.
The operators evaluated the quality of helical CT and color Doppler sonography as being good, suboptimal, or uninterpretable. All patients were evaluated by color Doppler sonography and helical CT with respect to the patency of the stent-graft and iliac arteries, the perigraft leak and its origin and outflow, and the complications related to the endovascular treatment. Only the examinations obtained within 7 days after implantation were compared.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Perigraft Leak
Helical CT revealed perigraft leaks in 22 patients (40%). Seventeen
patients were considered to have a type I endoleak. In four patients, the
endoleak was visible only on early images. In 20 patients, a perigraft leak
was suspected by color Doppler sonography. Discrepancies between helical CT
and color Doppler sonography were observed in eight patients (14.5%). In five
patients, a small perigraft leak clearly shown on helical CT was not found on
color Doppler sonography (Fig.
1A,1B).
Four of the patients were considered to have a type II endoleak. In two of
these patients, the leakage was visible only on the delayed images. One of
these five patients was lost during the follow-up; in four other patients, the
perigraft leak was small and disappeared spontaneously after 3-9 months. In
the 17 patients with a leak shown by both techniques, only two had spontaneous
thrombosis during the follow-up.
|
|
In three patients, CT did not confirm a perigraft leak suspected by color Doppler sonography. In all of these patients, the quality of the color Doppler sonogram was considered suboptimal by the operator because of intestinal gas or excess body weight. In two of the three patients, an angiography was performed that confirmed the results of the helical CT. Furthermore, in the same three patients, no modification of the aneurysmal size was revealed during a follow-up of 6-9 months (mean, 7 months).
The results of color Doppler sonography and CT for the diagnosis of endoleak are summarized in Table 1. For the diagnosis of endoleak, the sensitivity, specificity, and positive and negative predictive values of color Doppler sonography compared with helical CT were 77%, 90%, 85%, and 85%, respectively.
|
Seventeen patients had a perigraft leak shown on color Doppler sonography and helical CT (Figs. 2A,2B and 3A,3B). In seven of these patients, helical CT was superior to color Doppler sonography for determining the inflow or outflow of the perigraft leak (Fig. 3A,3B). Indeed, five inferior mesenteric arteries and two iliac endoleaks were identified only on helical CT.
|
|
|
|
Graft Patency
Color Doppler sonography and helical CT were equivalent for the evaluation
of graft patency. Grafts were patent in all patients as revealed on both
helical CT and color Doppler sonography during the first week after
implantation.
Complications
In three patients, only CT was able to reveal endovascular treatment
complications, including two retrograde iliac dissections subsequent to
endoluminal repair and one incomplete covering of the proximal part of the
abdominal aortic aneurysm with a stent-graft. In the latter patient, CT and
color Doppler sonography did not show a leak. However, color Doppler
sonography displayed an unusual motion of the aneurysmal wall.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
Sato et al. [18] have reported a high sensitivity and a high negative predictive value (97% and 98%, respectively) and a poor specificity and a low positive predictive value (74% and 66%, respectively) for color Doppler sonography. The difference between our study and the Sato et al. series was that the latter study was multicentered, comparing videotaped color Doppler sonography with arterial phase helical CT. Thompson et al. [19] also had a good concordance between CT and color Doppler sonography for perigraft leak detection. However, they used conventional CT with a thick collimation of 10 mm. Heilberger et al. [17] reported that color Doppler sonography could show sidebranch leaks not detected on CT. According to Sato et al., this may be explained by the failure of contrast medium to circulate inside the aneurysm at the time of imaging by CT. Biphasic helical CT with arterial and delayed phase acquisition may explain the superiority of helical CT in our study. Biphasic helical CT was reported to be superior to CT only when it was performed during the aortic enhancement phase. The combination of early and delayed acquisitions allowed the detection of a perigraft leak not visible or missed by the arterial phase alone in 11% of the patients [21]. In an in vitro study, Schurink et al. [22] showed that small perigraft leaks were not visualized by digital subtraction angiography and early CT angiography, whereas all perigraft leaks were visualized with a delayed CT angiography protocol. In the absence of delayed images in our study, the sensitivity and negative predictive value of color Doppler sonography would have been superior by 90% because in two patients with false-negative findings on color Doppler sonography, the delayed acquisition allowed the detection of perigraft leak. To our knowledge, the present article is the only study comparing color Doppler sonography with biphasic helical CT for all the patients.
Furthermore, sonography is known to have some important limitations. Not all examinations are of good quality. This limitation was observed by Sato et al. [18] and in the present study in which two patients had inadequate examinations and three patients had false-positive findings on suboptimal color Doppler sonograms. Moreover, the results of the color Doppler sonographic examinations are influenced by the experience of the operator. In the present study, all color Doppler sonographic examinations were performed by experienced physicians. Given the substantial operator dependency of sonography, the results of the present study may not be applicable to the practices of sonographers with less dedicated experience imaging aortic endografts. CT is a less operator-dependent technique and is more reproducible than color Doppler sonography. This factor is of primary importance in patients who have undergone endoluminal aortic repair and require close follow-up, considering that the long-term outcome of this technique is not yet available. Injection of an IV echo-enhancing agent could increase the sensitivity of color Doppler sonography for perigraft leak detection to a level comparable to CT [17, 23]. Nevertheless, this injection makes color Doppler sonography more expensive and time consuming.
Although Thompson et al. [19] claimed that sonography is superior to CT for revealing the origin of the perigraft leak, this result was not observed in the present study. Biphasic helical CT was superior to color Doppler sonography for detecting the origin of the perigraft leak and evaluating the patency of inferior mesenteric artery and lumbar arteries. According to a recent article [24], the ability of color Doppler sonography for the detection of the source of the leak was low.
One of the advantages of color Doppler sonography is its ability to reveal aortic wall motion. The pulsatile wall motion before and after endoluminal repair of an abdominal aortic aneurysm has been evaluated by Malina et al. [25]. They have shown that aneurysmal exclusion is followed by a considerable decrease in pulsatile wall motion. In patients with perigraft leak, pulsatile wall motion is 50% greater, but the prognostic interest of this observation remains to be seen. We did not systematically evaluate this sign in the present study. However, an unusual motion of the aneurysmal wall associated with a misplaced prosthesis was observed in one patient.
Finally, a wide range of complications are reported during and after stent-graft implantation. Results from the Eurostar registry (European collaborators on stent-graft techniques for aortic aneurysmal repair) show up to 16% operative and 18% systemic early complications (occurring within 1 month after the procedure) from endoluminal therapy [26]. The role of imaging in the detection of most of these complications is limited. Other rare complications are also reported after endoluminal repair, such as colonic ischemia, vertebral body ischemia, and renal infarction. These complications are mainly related to aortic branch occlusion. For these complications, CT remains clearly superior to sonography. The most common complications after stent-graft repair are perigraft leak, stent-graft migration, deformation, and graft thrombosis.
Color Doppler sonography correctly evaluates the flow within the stent-graft and the iliac limb [19]. However, color Doppler sonography remains inferior to CT for the evaluation of the complications related to the stent-graft implantation.
Although color Doppler sonography is reliable for the detection of a clinically significant leak, a perigraft leak is among the many factors needed for the surveillance of stent-grafts in an abdominal aortic aneurysm. Stent-graft deformation and migration are important parameters that cannot be evaluated by color Doppler sonography but are well depicted by helical CT with reconstruction and with abdominal radiographs. Moreover, the evaluation of an aneurysmal diameter is more accurate when measured on CT [27]. Finally, the length of the aneurysm is another important parameter [28] that is well measured and reproduced by helical CT but may be hazardous on color Doppler sonography.
This study has several limitations. First, the patient group was heavily weighted toward aortouniiliac stent-grafts that are less commonly used. In addition to being associated with the type I and II endoleaks, this type of device may also be associated with a leak related to the incomplete occlusion of the contralateral iliac artery. Second, the helical CT parameters used in this study (a collimation of 5 mm and a pitch of 1.2) are not the optimal parameters that are currently used with modern helical CT scanners. The choice of these parameters was determined by a helical CT scanner available at our institution at the beginning of the present study. With this scanner, we were not able to cover the aortoiliac region with a 3-mm collimation without heating the tube. This technique results in a wider effective section thickness than does a 3-mm collimation with a pitch of 2, which we are currently using. In addition, the reconstruction interval should optimally be 50% of the effective section profile. Thus, in this study, an interval of 3 mm would have been optimal. Third, we have compared the results of helical CT and color Doppler sonography in the immediate postoperative period. During this period, large leaks are more likely to be present. The higher prevalence of a larger leak in the immediate postoperative period may overestimate the true accuracy of sonography. Finally, the absence of unenhanced CT sections for the distinction of small leaks and calcifications could have been considered a limitation of this study. However, delayed acquisition has been reported to allow the distinction between small leaks and calcifications [21]. With the use of delayed acquisition, Golzarian et al. [21] found no need for unenhanced CT sections.
In our current practice, this study allowed us to reduce the number of contrast-enhanced helical CT examinations. Color Doppler sonography and abdominal radiography are performed every 3 months during the first year and every 6 months thereafter. Unenhanced CT and enhanced helical CT examinations are alternatively performed every 3 months during the first year and every 6 months thereafter.
In conclusion, in our experience, biphasic enhanced helical CT remains the best technique for the follow-up of abdominal aortic aneurysms after endoluminal repair. Helical CT is superior to color Doppler sonography for detecting the origin of the perigraft leak, the outflow vessels, and the complications related to the stent-graft procedure. Color Doppler sonography is a valuable tool for the detection of substantial perigraft leaks, whereas color Doppler sonography might fail to detect small perigraft leaks. Nevertheless, perigraft leaks that were missed by color Doppler sonography were without clinical significance and required no additional treatment. The main limitation of color Doppler sonography is its high rate of suboptimal examination. Color Doppler sonography cannot replace helical CT, but it can reduce the number of contrast media injections during follow-up. In association with unenhanced CT, color Doppler sonography may also be considered a valuable imaging technique for the follow-up of patients with contraindication for contrast medium injection.
Acknowledgments
We thank Pierre Alain Gevenois for his substantial contribution to this
manuscript.
|
TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
|---|
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
 |
|
  M. F. Giannoni, F. Fanelli, M. Citone, M. Cristina Acconcia, F. Speziale, and B. Gossetti Contrast ultrasound imaging: the best method to detect type II endoleak during endovascular aneurysm repair follow-up Interactive CardioVascular and Thoracic Surgery, June 1, 2007; 6(3): 359 - 362. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 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]
|
|
|
|
|
|
M. Macari, H. Chandarana, B. Schmidt, J. Lee, P. Lamparello, and J. Babb Abdominal Aortic Aneurysm: Can the Arterial Phase at CT Evaluation after Endovascular Repair Be Eliminated to Reduce Radiation Dose? Radiology, December 1, 2006; 241(3): 908 - 914. [Abstract] [Full Text] [PDF]
|
|
|
|
 |
|
 T. S. Maldonado and P. J. Gagne Controversies in the Management of Type 11 "Branch" Endoleaks Following Endovascular Abdominal Aortic Aneurysm Repair Vascular and Endovascular Surgery, January 1, 2003; 37(1): 1 - 12. [Abstract] [PDF]
|
|
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| HOME | HELP | FEEDBACK | SUBSCRIPTIONS | ARCHIVE | SEARCH | TABLE OF CONTENTS |
