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Revista da Associação Médica Brasileira

Print version ISSN 0104-4230

Rev. Assoc. Med. Bras. vol.57 no.1 São Paulo Jan./Feb. 2011

http://dx.doi.org/10.1590/S0104-42302011000100012 

ORIGINAL ARTICLE

 

Stent thrombosis in aortic aneurysm: evaluation by multidetector CT

 

 

Roberto de Moraes BastosI; Alvaro Razuk FilhoII; Roberto BlasbalgIII; Roberto Augusto CaffaroIV; Walter Khegan KarakhanianV; Fernando Pinho EstevesVI; Andre Paciello RomualdoVI; Antonio José da RochaVII

IProfessor/Instructor; Radiologist
IIM.D.; Assistant Professor of Faculdade de Ciências Médicas da Santa Casa de Misericórdia de São Paulo, São Paulo, SP, Brazil
IIIPhysician of Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo - USP, São Paulo, SP, Brazil
IVM.D.; Professor of Faculdade de Ciências Médicas da Santa Casa Misericórdia de São Paulo, São Paulo, SP, Brazil
VM.D.; Professor of Faculdade de Ciências Médicas da Santa Casa de São Paulo, São Paulo, SP, Brazil
VIM.D.; Irmandade da Santa Casa de Misericórdia de São Paulo, SP, Brazil
VIIM.D.; Professor of Faculdade de Ciências Médicas da Santa Casa de Misericórdia de São Paulo, São Paulo, SP, Brazil

Corresponding author

 

 


ABSTRACT

OBJECTIVE: To evaluate the demographic characteristics and imaging findings of thrombosis in a series of patients submitted to endovascular stent-graft repair of abdominal aortic aneurysm (ESGAAA).
METHODS: We evaluated the imaging features, which allowed the diagnosis of endoluminal thrombosis in a series of 30 patients undergoing ESGAAA and followed from 5 to 29 months, using 64-channel multidetector computed tomography (MDCT).
RESULTS: Thrombosis was diagnosed in 10 patients (33.3%), and in 3 of those patients, total thrombosis was observed in an iliac branch.
CONCLUSION: MDCT allowed the diagnosis of different types of endoluminal thrombosis in patients submitted to ESGAAA. The use of this minimally invasive diagnostic technique should be encouraged in clinical practice.

Keywords: Aortic aneurysm; tomography; thrombosis.


 

 

Introduction

Until the early 90's, open surgery was the only treatment for abdominal aortic aneurysm (AAA), with perioperative mortality rate for patients undergoing elective surgery ranging from 4% to 8.4% in specialized centers1,2,3. The continuous search for surgical techniques with lower mortality and morbidity rates led to the development of endovascular prosthesis and techniques to treat abdominal aortic aneurysm. They have been used in different regions of the world, being approved by the United States Food and Drug Administration (FDA) since 19994,5.

Endovascular surgery for AAA repair is not devoid of complications, which can develop during or after the procedure. However, the choice of this treatment modality has been justified when compared to conventional surgery1. Parietal thrombosis may develop as a small circumferential thrombus on graft's wall, or as a luminal occlusion of the stent, demonstrated in digital angiography (DA) or computed tomography (CT), with an estimated incidence of 3-19% of the cases of endovascular stent-graft repair of abdominal aortic aneurysm (ESGAAA)6,7,8,9,10,11.

Using a 64-channel multidetector CT (MDCT), we investigated a series of consecutive patients who underwent ESGAAA in order to assess the demographic characteristics and images of endoluminal thrombosis.

 

Methods

Patients

This transversal study was approved by the Research Ethics Committee of the Institution, and all patients signed an informed consent. From February to September 2007, 30 consecutive patients followed-up after ESGAAA (26 males and 4 females), ages 55 to 83 years (mean 70.9 years, median 72 years), were included in this study. All patients agreed to participate in the study. The followup period ranged from 5 to 29 months after surgery (mean 14.4 months, median 13.5 months). The proposed followed-up protocol included MDCT at 1, 3, 6, and 12 months in the first year after the surgery, followed by annual MDCT in cases with aneurism regression or stability. In those cases in which expansion on the aneurysm was observed, patients were followed-up with MDCT every three months. All patients were treated with aortoiliac abdominal stent grafts of the following brands: Talent®, Meditronic Vascular, Sunrise, Fla (n = 18); Excluder endoprothesis®, W.L. Gore & Associates, Sunnyvale, Calif (n = 1); Zenith®, Cook Inc, Bloomington, Ind (n = 8); and Apolo®, Nano Endoluminal, Florianópolis, Brasil (n = 3). To analyze the development of endoluminal thrombosis, grafts were grouped according to their material, and they were separated in Polytetrafluorethylene (PTFE) (Apolo® and Excluder endoprosthesis®) and Dacron/Polyester (Talent® and Zenith®).

Patients who refused to participate, and those who presented contraindications to the injection of iodinated contrast media or exams with ionizing radiation, as well as those with renal failure were excluded from the study.

Exams

MDCT 64-channel Brilliance equipment (Phillips, Eindhoven, Holland) was used for the exams. The exam covered the area between the diaphragm and common femoral arteries in three phases: pre-contrast, with collimation of 2.5 mm, 120 Kv, and 322 mAs; and post-contrast, arterial and venous phases, both with acquired collimation of 0.625 mm and reconstructed with 1.0 mm thickness, increment of 1.0 mm, Pitch of 0.703, rotation velocity of 0.75 per second, 120 Kv, and 350 mAs.

A dose of 1.5 mL/kg of contrast medium (mean of 100 ml per patient), with concentration of 300 mg of iodine per ml, was injected through a venous puncture with a 20-Gauge catheter in the antecubital vein, with an infusion pump at a rate of 5 ml per second, followed by 30 ml of normal saline. Post-contrast administration phases were performed using an attenuation detector mechanism placed in the area of the aorta, at the level of the celiac branch (bolus tracker) that, when reached 180 Hounsfield units (HU) determined by the arrival of the contrast medium, began scanning the arterial phase, followed by the venous phase attained 60 seconds after the first one. In all phases, apnea time ranged from 12 to 18 seconds.

Image analysis

All images were independently analyzed at a workstation (GE Medical Systems, Milwaukee, WI) by two radiologists (RMB and RB), with 11 and 15 years experience, respectively, and final results were obtained by consensus.

Data related to the integrity of the stents, presence or absence of luminal thrombus, characteristics and location of thrombus, as well as information related to the type of stent and its constituents were analyzed. All arterial phase images were used for tridimensional angiographic reconstitutions using appropriate volume rendering (VR) and maximum intensity projection (MIP) reconstruction algorithms.

Statistical analysis

To determine the site were thrombi are formed, the incidence and percentage were calculated. Fisher's exact test was used to compare the occurrence of thrombosis with stent's brand, as well as the group of stents according to the constituent material, formed by PTFE (Apolo® and Excluder endoprosthesis®) and Dacron/ Polyester (Talent® and Zenith®).

 

Results

All prosthesis used were intact and without signs of fracture on MDCT. Ten cases (33.3%) of endoluminal thrombosis were identified. Five of those (16.7%) showed partial aortic thrombosis; one (3.3%) had partial thrombosis of the aorta and right iliac branch; one (3.3%) had partial thrombosis of the right iliac branch; and three (10%) had partial thrombosis of the aorta and total thrombosis of the right iliac branch (Figure 1). Data are presented in Table 1.

 

 

All patients with complete right iliac branch thrombosis were smokers and had been treated for aneurysms of external iliac arteries by placing stent extensions and occluders of the internal iliac arteries. In two of them, thrombosis was diagnosed between 30 and 60 days after surgery, requiring surgical limb revascularization with crossed femorofemoral graft. The other patient presented thrombosis, diagnosed on control exam at six months, evolving with retroperitoneal and abdominal collateral circulation, without the need of new surgery.

Out of the 10 patients with endoluminal thrombosis, 8 were smokers, 2 had DM, and 1 had hypertension. No statistically significant relationship between the presence of thrombosis and these clinical conditions was identified using Fisher's exact test.

Among the brands of prosthesis associated with thrombosis, it was identified 1 case with Apolo®, 7 with Talent®, and 2 with Zenith®. A statistically significant difference in the presence of thrombosis among the brands was not observed.

Among the group of materials, one case of thrombosis in PTFE prosthesis (Apolo® and Excluder endoprosthesis®) and 9 cases in Dacron/Polyester prosthesis (Talent® and Zenith®) were identified. A significant difference in the presence of thrombosis among the material of the prosthesis was not observed.

 

Discussion

Endoluminal vascular prosthesis thrombosis represents one of the main complications of ESGAAA diagnosed by CT scan. Specialized literature highlights the following key factors determining the characteristic of stents thrombogenic material12, smoking, the need of adjuvant procedures, and the experience of the surgical team13. According to Thurnher et al.14, formation of semicircular thrombi can occur in up to 19% of the cases, usually not determinant of flow changes or clinical repercussion. Our results is in agreement with this observation, since all seven patients with partial thrombosis (23.3%) remained asymptomatic in clinical evaluations and subsequent MDCTs.

Occlusion of the blood vessel by thrombosis, which has an incidence of 1.5% to 10%, in general extending to the iliac branch, has as main triggering factor the marked tortuosity of the prosthesis or even prosthesis bending by aneurysmal remodeling14. It has been reported that the evolution of luminal thrombosis may be spontaneous resolution of the thrombus, embolization of distal limb branches, or even total occlusion of blood vessel10. According to Schunn et al.12, bifurcated prostheses have a greater chance of thrombosis- and embolization-related complications than tubular prostheses. The author reported an incidence of 10.5% of luminal thrombosis, 60% in bifurcated prosthesis and 13.3% in tubular prosthesis12.

In the present study, we identified an elevated rate of thrombosis (33%), regardless of the type of material or prosthesis used, which is above those reported in international literature.14 Despite the absence of statistical significance in this case series, the literature has emphasized that superposition of some clinical conditions, especially smoking, may contribute to endoluminal thrombi formation13.

We believe that the high incidence of endoluminal thrombosis in this series might be due to the greater diagnostic accuracy of the high-resolution of the 64-channel MDCT images used in this study. High-resolution fine cuts (1.0 mm) allowed the detection of small intraluminal thrombi, in addition to tridimensional angiographic reformatting and reconstruction using volume rendering (VR) and maximum intensity projection (MIP) reconstruction algorithms. In a recent study using the same specification equipment and similar protocol, Thomaz et al.10 observed an elevated rate of luminal thrombosis in ESGAAA follow-up.

Specific studies on inherent particularities of the diagnosis and late treatment of AAA in the Brazilian population are required. Tortuosity with greater longitudinal and transversal dilation of aortic aneurysm has been considered a risk factor for the development of endoluminal thrombosis14. Nevertheless, our results do not allow close evaluation of this aspect.

Despite the limitations inherent in this type of study, we believe that our results indicate relevant factors regarding the diagnosis of endoluminal thrombosis by MDCT. In the opinion of the authors, studies with larger series of patients, with longer follow-up, using the high resolution MDCT protocol, may contribute for better understanding of endoluminal thrombosis, besides providing precise diagnostic parameters and more adequate therapy.

 

Conclusion

Multidetector CT allowed the diagnosis of different types of endoluminal thrombosis in this series of patients who underwent ESGAAA. The use of MDCT in clinical practice should be encouraged in order to obtain the best use of this minimally invasive diagnostic tool in the followup and diagnosis of individuals undergoing ESGAAA.

 

References

1. Kaufman JA, Geller SC, Brewster DC, Fan CM, Cambria RP, LaMuraglia GM, et al. Endovascular repair of abdominal aortic aneurysms: current status and future directions. AJR Am J Roentgenol. 2000;175:289-302.         [ Links ]

2. Ernst CB. Abdominal aortic aneurysm. N Engl J Med. 1993; 328:1167-72.         [ Links ]

3. Lawrence PF, Gazak C, Bhirangi L, Jones B, Bhirangi K, Oderich G, et al. The epidemiology of surgically repaired aneurysms in the United States. J Vasc Surg. 1999; 30:632-40.         [ Links ]

4. Lederle FA. Abdominal aortic aneurysm - open versus endovascular repair. N Engl J Med. 2004; 351:1677-9.         [ Links ]

5. Parodi JC, Marin ML, Veith FJ. Transfemoral, endovascular stented graft repair of an abdominal aortic aneurysm. Arch Surg.1995; 130:549-52.         [ Links ]

6. Dorffner R, Thurnher S, Polterauer P, Kretschmer G, Lammer J. Treatment of abdominal aortic aneurysms with transfemoral placement of stent-grafts: complications and secondary radiologic intervention. Radiology. 1997; 204:79-86.         [ Links ]

7. Doffner R, Thurnher S, Youssefzadeh S, Winkelbauer F, Hölzenbein T, Polterauer P, et al. Spiral CT angiography in the assessment of abdominal aortic aneurysms after stent grafting: value of maximum intensity projections. J Comput Assist Tomogr. 1997; 21:472-7.         [ Links ]

8. Sakai T, Dake MD, Semba CP, Yamada T, Arakawa A, Kee ST, et al. Descending thoracic aortic aneurysm: thoracic CT findings after endovascular stent-graft placement. Radiology. 1999; 212:169-74.         [ Links ]

9. Silberzweig JE, Marin ML, Hollier LH, Mitty HA, Parsons RE, Cooper JM, et al. Aortoiliac aneurysms: endoluminal repair-clinical evidence for a fully supported stent-graft. Radiology. 1998; 209:111-6.         [ Links ]

10. Thomaz FB, Lopez GE, Marchiori E, Magalhães FV, Magalhães IF, Kuroki IR, et al. Avaliação pós-operatória do tratamento endovascular de aneurismas da aorta abdominal por angiotomografia com multidetectores. Radiol Bras. 2008; 41:213-7.         [ Links ]

11. Mita T, Arita T, Matsunaga N, Furukawa M, Zempo N, Esato K, et al. Complications of endovascular repair for thoracic and abdominal aortic aneurysm: an imaging spectrum. Radiographics 2000; 20:1263-78.         [ Links ]

12. Schunn CD, Krauss M, Heilberger P, Ritter W, Raithel D. Aortic aneurysm size and graft behavior after endovascular stent-grafting: clinical experiences and observations over 3 years. J Endovasc Ther. 2000; 7:167-76.         [ Links ]

13. Buth J, Laheij RJF. Early complications and endoleaks after endovascular abdominal aortic aneurysm repair: report of a multicenter study. J Vasc Surg. 2000; 31:134-46.         [ Links ]

14. Thurnher S, Cejna M. Imaging of aortic stent-grafts and endoleaks. Radiol Clin North Am. 2002; 40:799-833.         [ Links ]

 

 

Corresponding author:
Roberto de Moraes Bastos
Rua Bergamota, 470 - Apt. 81 Bloco C
CEP: 05468 000, São Paulo, SP, Brazil
Phone: (11) 3021-1658 / 99047102 / Fax: (11) 2176-7333
robertomb@uol.com.br

Submitted on: 07/07/2010
Approved on: 11/07/2010
Conflict of interest: None.

 

 

Received from Irmandade da Santa Casa de Misericórdia de São Paulo and Fleury Medicina e Saúde, São Paulo, SP

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