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Vascular and Interventional Radiology |
1 From the Departments of Radiology (J.G., N.R., R.S., C.E., S.C.K., H.J.B.) and Thoracic and Vascular Surgery (K.H.O., L.S.P., R.P.), University of Ulm, Steinhövelstrasse 9, 89075 Ulm, Germany. Received May 20, 1998; revision requested July 14; final revision received February 18, 1999; accepted June 8. Address reprint requests to J.G. (e-mail: petra.silber@medizin.uni-ulm.de).
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Abstract |
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 TOP Abstract IntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS: Fifty patients aged 26–79 years underwent endovascular repair of traumatic (n = 4) or arteriosclerotic (n = 46) aortic aneurysms (four thoracic, 46 infrarenal). Radiographic examinations in three planes and helical CT were performed 1 week after implantation and every 3 months thereafter. Angiography was performed when there was evidence of a leakage at CT.
RESULTS: CT demonstrated evidence of leakages in 13 patients. Broad-based leakages immediately adjacent to the prosthesis were termed "perigraft leakages." If the area most affected by the leakage lay along the border of the aneurysm, then retrograde leakages were apparent at angiography. If the leakage was ventral to the prosthesis, then its source was the inferior mesenteric artery; if it was dorsolateral, then it was supplied by either the lumbar arteries or the median sacral artery through the hypogastric artery. One circumferential leakage could not be evaluated adequately at CT or angiography. Radiography depicted a rupture of the stent mesh in the middle of the prosthesis. Selective angiography demonstrated all types of leakages and permitted CT classification.
CONCLUSION: The cause of a leakage can be determined with CT on the basis of its configuration and location in the majority of cases.
Index terms: Aneurysm, aortic, 94.731, 94.732, 98.731, 98.732 • Angiography, 94.1211, 94.1222, 98.1211, 98.1222 • Arteries, CT, 94.12911, 94.12912, 94.12914, 94.12915, 98.12911, 98.12912, 98.12914, 98.12915 • Arteries, grafts and prostheses, 94.1268, 98.1268 • Computed tomography (CT), comparative studies, 94.12911, 94.12912, 94.12914, 94.12915, 98.12911, 98.12912, 98.12914, 98.12915
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Introduction |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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MATERIALS AND METHODS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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All patients were involved in a strict follow-up protocol as follows: To monitor the position and closure of the prostheses, three-phase helical CT of the abdomen or thorax was performed by using a Twin CT scanning unit (Elscint, Haifa, Israel) and the following parameters: Without contrast material, a pitch of 1.5, section thickness of 8.8 mm (effective), and increments of 10 mm were used; with contrast material (iopamidol [Solutrast 300]; Bracco-Byk Gulden, Konstanz, Germany) in the early phase (volume, 150 mL; flow rate, 2.5 mL/sec; scanning delay, 45 seconds), a pitch of 1.0, section thickness of 5.5 mm, and increments of 2.5 mm were used; and with contrast material (iopamidol) in the late phase (scanning delay, 100 sec), a pitch of 1.5, section thickness of 5.5 mm, and increments of 2.5 mm were used. Multiplanar CT evaluation was performed by two experienced radiologists (J.G., N.R.) in consensus. The findings that were evaluated at CT and angiography were leakage location, configuration, contact with the stent-graft, and contact with the aneurysmal margin. At angiography, the cause of the leakage (eg, perigraft leakage) and the feeding artery, as identified by the same two radiologists in consensus, who were aware of the CT findings, were evaluated.
The angiographic examination during the 1st week after the aneursymal repair to exclude leakages was performed postoperatively in the first 40 cases. In the remaining patients, considerations of radiation exposure limited angiography to those cases in which there were pathologic findings at CT.
Every 3 months, the patients underwent three-phase helical CT to exclude leakages and conventional radiography in three planes to evaluate the integrity of the stent. The absolute size of the leakages was not considered; we were interested only in the leakage's location and relation to the prosthesis and aneurysm. In those cases in which there was evidence of a leakage at CT, intraarterial angiography was performed within 2 days. The protocol included abdominal scout aortography in at least two planes (30 mL at a flow rate of 12 mL/sec in a 60-second-duration series to detect late leakages). For diagnostic angiography, transfemoral access was used in all cases. After survey aortography with a pigtail catheter to search for leakages, a Cobra or sidewinder catheter was placed at the proximal end of the prosthesis. Visualization of the internal iliac artery bilaterally (with manual injection of 10 mL of contrast material) and of the superior mesenteric artery (with 25 mL of contrast material at a flow rate of 5 mL/sec) was then achieved. If the selective catheterization of the contralateral internal iliac artery proved to be unsuccessful, then angiography was repeated the next day on the contralateral side. The follow-up period ranged from 1 to 33 months (average, 6.9 months). Written informed consent was obtained from all patients.
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RESULTS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Six leakages were ventral to the aortic prosthesis, whereas four were lateral. In three cases, the prosthesis was surrounded by leakages on all sides. On the basis of the location and configuration of the leakage and its spatial relationship with the prosthesis and the margins of the aneurysm, it was possible to determine the immediate cause of the leakage so that classification could be performed (Figs 1–5).
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In three patients with perigraft leakages, the leakages were from more than one source. This, however, became apparent only at the first follow-up CT examination after treatment of the most proximal leakage.
Two patients with thoracic prostheses had leakages. In one of these cases, it appears that the stent mesh became torn during the insertion of the prosthesis, whereas in the other case, the stent was too short and had to be lengthened in a second procedure. When the leakages persisted for longer than 3 months, therapeutic embolization or stent placement was performed as described elsewhere (1).
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The method of covering the lumbar arteries and the inferior mesenteric artery with stents allows only retrograde flow in these vessels and, possibly, access for backflow leakages. Alternatively, one would have to perform embolization in every vessel before inserting the prosthesis to change this method (7).
Because the reduction in size of the aneurysm after endovascular therapy is limited, even in the absence of leakages, the hemodynamic significance of a leakage cannot be immediately determined from findings at CT. Blum et al (8) suggested that in the first 12 months, a size reduction of 2–4 mm is to be expected, whereas in the next 24 months, a more pronounced reduction of 5–15 mm may be observed. Malina et al (3), Broeders et al (12), and Matsumura et al (13) found that even minor leakages or collateral perfusion inhibited the reduction of the aneurysm diameter in patients after successful endovascular aneurysm repair.
Resnikoff et al (14) examined 831 patients who underwent nonresective treatment of infrarenal abdominal aortic aneurysms by means of proximal and distal ligation of the aneurysmal sac combined with aortic bypass grafting, and reported only 17 (2%) retrograde leakages, which were supplied by the lumbar, hypogastric, or inferior mesenteric arteries. A high percentage of these patients had ruptures during the follow-up period. These data underscore the importance of an adequate screening protocol for the early detection of leakages.
The findings of Resnikoff et al (14) and our data indicate that CT is the single most sensitive method for detecting leakages. Although color Doppler ultrasonography (US) is a useful method for demonstrating leakages, its application is limited because a majority of patients with aortic leakages tend to be older and obese, and, thus, some segments of the infrarenal aorta may not be adequately depicted. Due to the physical properties of the thorax, the use of US for imaging thoracic prostheses is impossible. Aortography also fails in a large number of cases, particularly in the depiction of small leakages, although superselective procedures that take into consideration all the potentially involved arteries often demonstrate these leakages. The findings at CT may serve as a road map for pinpointing the site of leakage.
Although we examined a small group of patients in this study, we were able to observe certain regularly occurring factors. Broad-based leakages directly adjacent to the prosthesis are due to leakage at the sites of the terminal end of the stent-grafts. These correspond to perigraft leakages according to the classification of White et al (10,11). Ventral leakages that do not have a direct connection to the prosthesis are, in our opinion, supplied by the inferior mesenteric artery, which is fed by the marginal artery or Riolan anastomosis. Leakages that have a base that is dorsolateral to the margin of the aneurysm are supplied by either the lumbar arteries or the median sacral artery, which is fed by the hypogastric artery. Findings at CT permit an exact classification of the leakage. CT-based classification of leakages may reduce the need for extensive angiographic studies, because the source of a leakage may be indicated directly by the CT findings.
Conventional fluoroscopy, which appears to be a very sensitive method for detecting rupture of the stent mesh, has long-term importance. This appears to be particularly true in cases in which the rupture is due to material fatigue, which may be an issue in older prostheses. The diagnosis of such ruptures is often more difficult to make with angiography or CT, because all that one sees is a large leakage.
In our series, a graft rupture that occurred in a patient with an aneurysm of the thoracic aorta may have been due to the advancing of the prosthesis during implantation. The rigid implantation instrument must be advanced into the curvature of the arch, particularly the aortic arch, at which point the material approaches the limit of its endurance.
Because, to our knowledge, no confirmed results have indicated the effectiveness of an opposite protocol, it has been the practice in our department to recommend the treatment of all leakages that do not spontaneously close within 3 months, regardless of their cause. Interventional occlusion of the leakage is possible in most cases. Usually, embolization with metal coils is attempted first; this procedure is also safe and effective for treating proximal paraprosthetic leakages (5). Here, the goal is not so much the closure of the perfused lumen of the aneurysmal sac but rather the elimination of the source of the blood flow to prevent the blood pressure from acting against the aneurysmal wall (5,15). Although the use of glue, such as histoacryl, is substantially less expensive, it may result in damage to nerve tissue. In theory, there is the additional risk of glue being carried into the lumbar arteries, which, in the worst-case scenario, might cause occlusion of the anterior spinal artery.
Usually, embolization of a lumbar artery is easy from a technical standpoint (16). Although the irregular course of the vessels often prevents the catheter from being advanced directly into the lumbar artery, proximal occlusion of the tributary arteries that feed the iliolumbar artery on both sides usually results in sufficient thrombosis of the leakage. More difficult are those cases of an internal iliac artery unilaterally covered by a stent in which cross-filling through the collateral vessels from the contralateral internal iliac artery results in reflux reperfusion of the aneurysm.
In cases of refilling of the aneurysm through the inferior mesenteric artery, embolization of the leakage through the superior mesenteric artery can be performed. In the absence of Riolan anastomosis, the marginal artery, which is almost always identifiable, may be used to access the inferior mesenteric artery (17). The results of CT known at the time of angiography can guide selective catheterization to find and occlude the leakage.
It is conceivable that leakages have an evacuating vessel in addition to the artery that feeds them. Otherwise, a slow process of thrombosis is likely. Many leakages, however, even small ones, remain open for many months; selective angiography in the aneurysmal sac often depicts these evacuating vessels, which escape detection on angiographic scout images. Despite the occlusion of the proximal feeding artery, there remains the danger that the leakage is maintained by other tributary arteries. For this reason, to prevent the development of collateral vessels, our recent departmental practice has been to attempt not only occlusion of the feeder artery but also embolization of the entire open aneurysmal sac.
In conclusion, CT is highly sensitive for the detection of leakages. On the basis of the configuration and location of the leakage in relation to the prosthesis and aneurysm, as depicted at CT, the cause and/or the feeding artery may be confirmed at angiography. Fluoroscopy is of particular importance in detecting ruptures of the stent mesh secondary to material fatigue.
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Footnotes |
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References |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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In our collective series, these leakages occurred exclusively on the right side of the body. 
In two patients, the prosthesis was too short and thus was lengthened during a second repair procedure. The third case was that of a large leakage, the cause of which could not be determined at either CT or angiography. Radiographs showed rupture of the stent mesh.
