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Vascular and Interventional Radiology |
1 From the Department of Cardiovascular and Interventional Radiology, Stanford University Medical Center, 300 Pasteur Dr, Suite H3630, Stanford, CA 94305-1056 (T.S., M.D.D., C.P.S., T.Y., A.A., S.T.K., M.K.R., D.Y.S.), and the Department of Radiology, Fukui Medical University School of Medicine, Fukui, Japan (N.H.). Received April 1, 1998; revision requested June 25; revision received September 14; accepted December 16. Address reprint requests to M.D.D. (e-mail: mddake@stanford.edu).
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Abstract |
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MATERIALS AND METHODS: From 1992 to 1996, 85 patients with thoracic aortic aneurysm underwent stent-graft placement. In 63 patients, thoracic CT scans were obtained both before and within 10 days after placement. The CT findings were retrospectively studied, and their clinical effect analyzed. In 20 of 63 patients, long-term follow-up CT findings were also evaluated.
RESULTS: After stent-graft placement in the 63 patients, CT demonstrated an increase in pleural effusion in 46 (73%), periaortic changes in 21 (33%), perigraft leak in 13 (21%), atelectasis in six (10%), mural thrombus within the stent-graft in two (3%), and new aortic dissection in one (2%). The mean maximum diameter of the aneurysm was 58.8 mm before and 60.0 mm after stent-graft insertion. Sixty-two (98%) patients were successfully treated until discharge. Interventional procedures were performed to eliminate the leakage into the aneurysm sac in 10 patients with perigraft flow depicted at CT. Other complications were managed conservatively.
CONCLUSION: Thoracic CT is useful in the treatment of patients after stent-graft insertion for the management of descending thoracic aortic aneurysm.
Index terms: Aneurysm, aortic, 563.732, 943.73 • Aorta, grafts and prostheses, 563.1269, 943.1268 • Aorta, interventional procedures, 563.1269, 943.1268
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Introduction |
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In our institution, patients treated with stent-grafts routinely undergo a thoracic computed tomographic (CT) examination before their discharge to evaluate patency of the graft and the possibility of perigraft leak or other complications. Several changes depicted at thoracic CT have been reported after stent-graft insertion, such as an increase in pleural effusion (1), but we believe detailed CT findings after stent-graft placement in the thoracic aorta have not been well described. The purpose of this study was to analyze the findings at thoracic CT after stent-graft insertion in relation to the indication for treatment, aneurysm anatomy, and final outcome and, thus, to clarify the clinical effect of these findings on the treatment of the patients.
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MATERIALS AND METHODS |
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The endovascular stent-graft was custom designed for each patient and comprised a stainless steel endoskeleton consisting of modified Z-stents (Cook, Bloomington, Ind) covered with woven polyester graft material (Cooley Veri-Soft; Meadox/Boston Scientific, Watertown, Mass). All procedures were performed in the operating room with general anesthesia. The femoral artery, iliac artery, or abdominal aorta was surgically exposed and a 24-F Teflon sheath and polyethylene dilator were introduced over the guide wire and advanced with fluoroscopic guidance until the sheath was positioned proximal to the aneurysm. Then, the stent-graft was advanced through the Teflon sheath by using a solid pusher and was deployed at the appropriate position by holding the pusher firmly in position and quickly withdrawing the sheath.
CT was performed with a whole-body scanner (Somaton Plus-S, Siemens Medical Systems, Iselin, NJ, or CT HiSpeed Advantage, GE Medical Systems, Milwaukee, Wis) with capability for spiral scanning and three-dimensional reconstruction (7,8). The patient was instructed to hyperventilate and maintain the same degree of inspiration for 30 seconds. After placement of a 20-gauge intravenous catheter into an antecubital vein, a 150-mL bolus of nonionic iodinated contrast media (Isovue 300; Squibb, New Brunswick, NJ) was administered at a flow rate determined to deliver the volume of contrast media in a period of time equivalent to the duration scanning. A delay after the initiation of the contrast media infusion was calculated for each patient on the basis of findings at dynamic scanning performed through the level of interest after injection of a 20-mL bolus of contrast media. After the predetermined delay, spiral scans were obtained with 3-mm collimation at a table speed of 5 or 6 mm/sec (pitch, 1.7 or 2.0), depending on the required volume of interest. The spiral acquisition was reconstructed into axial sections with 5–9-mm collimation every 2–6 mm to achieve at least 33% overlap.
The CT scans were retrospectively interpreted in an independent manner by three experienced radiologists (T.S., T.Y., A.A.). Subsequently, final consensus agreement was achieved regarding the CT findings in each case. Findings on CT scans obtained after stent-graft placement were compared to those evident before placement with special attention to the following features: pleural effusion, atelectasis without massive pleural effusion, periaortic changes, perigraft leak, and other complications related to stent-graft placement. In addition, the maximum diameter of the aneurysm was compared on the CT scans obtained before and after placement. The CT scans were interpreted without knowledge of three-dimensional reconstruction, angiographic, or chest radiographic findings or patient prognosis.
Passive atelectasis associated with massive pleural effusion was commonly observed, but it was excluded from evaluation as a separate pathologic finding because it was not considered a primary process.
Aortic or periaortic changes evident at CT included aortic wall thickening, periaortic effusion, and periaortic atelectasis. Aortic wall thickening was diagnosed when the aortic wall was thicker on the postplacement than on the preplacement CT scans. Periaortic effusion was diagnosed when a fluid collection was observed around only the descending aorta without any other effusion identified on the same image. Periaortic atelectasis was diagnosed when focal atelectasis was noted adjacent to the aorta without atelectasis evident in other areas on the same image. In this study, if these findings existed on a CT scan before stent-graft placement and were unchanged on the postplacement CT images, they were not considered abnormal findings due to the stent-graft placement.
In 20 of the 63 patients, long-term follow-up CT scans (mean, 388 days; range, 6 months to 3.5 years) were also available for evaluation.
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RESULTS |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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After stent-graft insertion in the 63 patients, fever (>38°C) was recorded in 23 (37%) and leukocytosis (>11,000/µL [11.0 x 109/L]) in 48 (76%). In general, these findings were self-limited and improved within 7 days in all cases. Blood was cultured in 10 patients. No growth was observed in any culture.
In all 63 patients, CT images after stent-graft deployment were without major artifacts caused by the stent-graft. Minimal artifacts caused by the stent-graft were a relatively common finding on postplacement CT scans, but they did not prohibit interpretation of the images.
CT findings in the 63 patients are summarized in Table 1. The amount of pleural effusion increased in 46 (73%) patients, did not change in 10 (16%), and decreased in seven (11%). In the 46 patients with increased pleural effusion (Fig 1), the amount of pleural effusion increased on both sides of the pleural cavity in 27 (43%), on only the left side in 15 (24%), and on only the right side in four (6%). None of the patients underwent chest tube drainage, and all were treated conservatively. In all cases, a subsequent decrease in pleural effusion was confirmed at chest radiography before discharge. In all 13 patients with long-term follow-up CT scans, resolution of the effusion was confirmed. Atelectasis without massive pleural effusion was observed in six (10%) patients. Five of the six patients were treated conservatively with medication or nebulizer therapy, and their improvement was confirmed before discharge on the basis of findings at chest radiography, clinical symptoms, or laboratory data. In the remaining patient, a metallic endobronchial stent was placed 18 hours after stent-graft deployment to treat postplacement left-lung atelectasis (Fig 2). Before stent-graft placement in this patient, the left main bronchus had been noted to be severely compressed by the aneurysm. The patient recovered uneventfully after placement of the endobronchial stent, and complete resolution of the atelectasis was depicted at radiography 12 hours after the procedure.
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Aortic or periaortic changes were observed in 21 (33%) of the 63 patients. These findings included aortic wall thickening in 13, periaortic atelectasis in 15, and periaortic effusion in four. In 20 of the 21 patients, there was no associated back or chest pain. One patient with a periaortic change depicted at CT experienced back pain. Arteriography was performed, and no abnormalities were identified. The patient was observed, and an oral antiinflammatory medication was administered. The back pain disappeared completely, and he was asymptomatic 6 days after stent-graft placement. In 10 of the 21 patients, long-term follow-up CT scans were available for evaluation. In all cases, the abnormal findings disappeared without any specific treatment.
A small amount of mural thrombus lined the stent-graft on postplacement CT scans in two (3%) asymptomatic patients.
Aortic dissection not evident at preprocedural CT was detected in one (2%) patient after stent-graft deployment. In this patient, the dissection was located in the aortic arch and was presumably caused by a retrograde injury from introduction of the stent-graft delivery system. The patient was hemodynamically stable and experienced no back or chest pain. He was treated medically because he was considered a poor surgical risk and was alive without symptoms 36 months after the procedure.
Pneumonia was diagnosed in one patient, who was treated with antibiotics and recovered without sequelae.
The maximum diameter of the aneurysm increased (+3 mm or more) in 18 (29%) of the 63 patients, did not change (from -3 to +3 mm) in 36 (57%), and decreased (-3 mm or more) in nine (14%) (Table 2A). The mean maximum diameter of the aneurysm before stent-graft placement was 58.8 mm and within 10 days after the procedure was 60.0 mm. Among the 13 patients with perigraft leak, the maximum diameter of the aneurysm after stent-graft deployment was larger in two (15%), the same in 10 (77%), and smaller in one (8%) (Table 2A). Among the 50 patients without perigraft leak, the maximum diameter of the aneurysm after stent-graft deployment was larger in 16 (32%), the same in 26 (52%), and smaller in eight (16%) (Table 2A). No interventional procedure was performed in the patients with an aneurysm that enlarged without evidence of perigraft leak. At long-term follow-up CT (mean, 388 days; range, 6 months to 3 years) in 20 patients, the mean maximum diameter of the aneurysm was 59.5 mm before stent-graft placement, 60.8 mm shortly after placement, and 58.7 mm more than 6 months after placement. In a comparison of CT scans obtained shortly after and more than 6 months after stent-graft placement, the diameter of the aneurysm increased in three (30%) of 10 patients with no leak, in two (25%) of eight patients with a treated leak, and in one (50%) of two patients with a persistent leak (Table 2B).
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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In our study, development of pleural effusion or increase of an existing pleural effusion, either unilateral or bilateral, was a very common finding (73%) after thoracic aortic stent-graft placement. In most cases, it was managed successfully with conservative therapy including appropriate medication. No patient required external drainage with a chest tube. CT was an excellent modality for the detection and follow-up of pleural effusion and could clearly show the response to treatment.
Pneumonia or atelectasis without massive pleural effusion was demonstrated in 10% of our patients. Because most patients had evidence of inflammation such as leukocytosis or high fever immediately after the stent-graft placement, CT was a helpful tool to diagnose pneumonia or atelectasis and to prompt use of medications such as antibiotics or nebulizer therapy. The cause of atelectasis was not clear, but it may be related to general anesthesia. Atelectasis is a recognized complication of endobronchial intubation and mechanical ventilation (10,11). In one patient, a metallic endobronchial stent was placed because the descending thoracic aortic aneurysm was seen at CT to mechanically compress the left main bronchus (Fig 2). CT was useful in this case to determine the choice of treatment for atelectasis because it clearly demonstrated the bronchial stenosis due to external compression by the aneurysm.
Perigraft leak is relatively common and is one of the most disappointing complications of stent-graft treatment of aortic aneurysm because it may lead to failure of the therapy (12–15). Indeed, a perigraft leak with persistent flow in the aneurysm sac is potentially fatal and may cause aneurysm rupture (16). Consequently, it is our policy to detect and aggressively treat a perigraft leak as soon as possible. The initial detection of perigraft leak may occur at angiography in the operating suite immediately after stent-graft deployment. Unfortunately, however, there are several limitations in the operating room to the detection of a perigraft leak. The angiographic equipment we used was a mobile C-arm unit, which does not produce image quality comparable to that achieved with a stationary unit in the radiology suite. The ideal angulation to view the aneurysm and its necks was difficult to obtain because of limitations in C-arm angulation, the surgical table, and the ability of the unit to optimally compensate for the wide range of tissue densities in the chest. Rozenblit et al (12) reported in their series of stent-graft treatment for abdominal aortic aneurysm that CT depicted perigraft leak in four of seven patients whereas angiography in the operating room depicted it in only one.
The effectiveness of selective coil embolization of a perigraft tract for the treatment of perigraft leak was previously reported (9). Once a perigraft leak is detected at CT, our strategy is prompt treatment with coil embolization or placement of an additional stent-graft. In this series, leaks were successfully managed endoluminally before discharge in eight of 13 patients.
A new dissection in the aortic arch and ascending aorta was depicted at CT in one case. In general, the management philosophy for type A dissection is surgical repair, but this patient was treated medically because he was not a surgical candidate.
Aortic or periaortic changes are also relatively common findings and were detected in 33% of our patients. In all cases, the changes were not associated with any clinical symptoms, appeared self-limited, and were completely resolved at long-term follow-up CT without any treatment other than antiinflammatory drugs.
Periaortic changes and increased pleural effusion are commonly encountered, but their causes are unknown. They may represent reactive inflammatory processes because they are frequently associated with elevated fever and leukocytosis. Previously, Sapoval et al (17) reported transient perivascular thickening evident at CT after placement of a stent-graft in the iliac artery. Perivascular soft-tissue changes are also reported at magnetic resonance imaging after insertion of a polyester-covered stent in the femoral, iliac, or subclavian arteries (18,19). In both sheep and swine models, histologic examination shows an infiltration of inflammatory cells adjacent to the polyester 1–4 weeks after stent-graft insertion (20,21). The authors speculate that such inflammatory reactions are responsible for the perivascular changes noted on imaging studies. The polyester graft material, not the stainless steel stent, is considered responsible for the inflammatory reaction (19–25). It may be a foreign-body reaction to polyester (25), or it may be due to the accumulation of proinflammatory substances as part of its processing (19).
A thin focal lining of mural thrombus was rarely encountered at CT after stent-graft placement. In our experience, no specific treatment was required, and there were no instances of clinical symptoms including embolization or progression of the clot on subsequent CT scans.
Change in the diameter of the aneurysm is a finding not well understood. The maximum diameter increased slightly after stent-graft placement in 30% of our patients without evidence of perigraft leak. In 30% of the patients without perigraft leak who underwent long-term follow-up CT, the caliber of the aneurysm further increased compared with its diameter at CT immediately after stent-graft placement. To date, there have been no cases of rupture in this group. In the previous literature of endovascular treatment of abdominal aortic aneurysms (12), it was suggested that any enlargement of the aneurysm after treatment indicates a failure of the procedure. In our experience, however, a slight enlargement of the aneurysm diameter was a common finding after stent-graft placement. The mechanism of change in aneurysm caliber is unknown. If it is not associated with perigraft leak at CT, our current practice is to continue CT observation every 6 months without immediate intervention. Further study is necessary to clarify the real clinical effect and possible mechanism of the changes in aneurysm diameter because our long-term follow-up data include a small number (n = 20) of patients with relatively short-term follow-up (mean, 388 days).
In summary, several abnormal findings were detected at thoracic CT after stent-graft insertion for the treatment of descending thoracic aortic aneurysm. Pleural effusion was a common finding (73%) after stent-graft insertion, but it could be managed conservatively without external drainage. Perigraft leak was detected in 21% of our patients, and most of them were successfully treated endoluminally. Atelectasis was observed in 16% of our patients, and most of them could be treated with appropriate medication. Periaortic changes were relatively common (33%), but no treatment was necessary. The other complications were rarely encountered.
In conclusion, thoracic CT is useful in the treatment of patients after stent-graft insertion for management of descending thoracic aortic aneurysm. The clinical importance of changes in the aneurysm diameter after stent-graft placement remains unknown but is an important issue that requires clarification before this therapy can be recommended for general clinical use.
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Footnotes |
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