FDG-PET and FDG-PET/CT for Diagnosing Infection in Patients with Multiple Vascular Bypass Grafts: A Report of Two Cases
Article Outline
2-Deoxy-2-[18F]fluoro-d-glucose (FDG) positron emission tomography (PET) is an established imaging modality in the fields of clinical oncology, cardiology and neurology, and could be useful for the diagnosis of vascular prosthetic graft infection. The technology of combining FDG-PET and computed tomography (CT) images, acquired in a single session, is gaining popularity. Several reports proposed the application of both FDG-PET and FDG-PET/CT in the diagnosis and management of vascular prosthetic graft infection. This case report highlights the usefulness of FDG-PET and FDG-PET/CT as noninvasive diagnostic modalities for patients with multiple vascular prosthetic bypass grafts susceptible for infection.
Keywords: FDG-PET, FDG-PET/CT, Vascular prosthesis, Infection
Introduction
Vascular prosthetic graft infection remains an uncommon, but a severe complication in vascular surgery, associated with a high rate of major morbidity and mortality. Despite the use of systemic antibiotic prophylaxis and prevention of risk factors, graft infection occurs after 1–6% of all prosthetic vascular reconstructions.1, 2 Although the clinical presentation is usually straightforward, an intracavitary graft infection may be non-specific and difficult to diagnose, especially when multiple vascular bypass grafts are involved.
Computed tomography (CT) is considered the most efficacious imaging modality for diagnosing vascular graft infection, with a sensitivity and specificity of 94% and 85%, respectively.3 Magnetic resonance (MR) imaging, gallium scanning and labeled white blood cell scanning are complementary tests in ambiguous cases.
Positron emission tomography (PET) with 2-deoxy-2-[18F]fluoro-d-glucose (FDG) has been proposed as an adjunct imaging modality to establish the diagnosis of vascular prosthetic graft infection.4, 5, 6, 7, 8, 9 Recently, a comparative study showed that the efficacy of FDG-PET was superior to that of CT in the diagnostic assessment of patients with suspected aortic graft infection.5 The fusion of simultaneously acquired FDG-PET and CT images enables a precise localization of any abnormal FDG uptake in the vascular graft prosthesis, leading to a potential new diagnostic modality of infected vascular grafts. However, the discriminating role of this imaging modality in patients with multiple vascular prosthetic bypass grafts remains unclear.
Case Report
Patient 1
A 57-year-old female with a history of heavy smoking, hypertension and chronic obstructive pulmonary disease presented to our outpatient clinic with disabling claudication. MR angiography revealed diffuse peripheral atherosclerotic disease, with an occlusion of the left external iliac artery, for which a percutaneous transluminal angioplasty (PTA) and stent placement was performed. The stent blocked within a month. The patient underwent subsequently an extra-anatomical right-to-left crossover femoro-femoral bypass procedure with a 6-mm ringed polytetrafluorethylene (PTFE) graft. Within seven months, MR angiography showed a complete obstruction of the crossover bypass graft. Therefore a left ilio-femoral bypass with 6-mm ringed PTFE bypass graft was performed with good result.
Two years after placement of the crossover femoro-femoral bypass graft, she represented in the outpatient clinic, with a red and painful mass in her left groin. This was treated by drainage and intravenous antibiotics. Because of a persistent leucocytosis, vascular graft infection was suspected and CT and a technetium-99m-HMPAO-labeled leukocyte scan were performed. Both showed no conclusive diagnosis, so the patient was referred for FDG-PET/CT imaging.
After the injection of FDG, an examination was performed using the hybrid PET/CT scanner. No contrast was administered for CT acquisition, since CT was only used for attenuation correction and fusion of PET emission data with the corresponding CT images. The PET/CT fused images showed an abnormal high uptake of FDG localized to the femoro-femoral crossover bypass graft (Fig. 1), which confirmed the diagnosis of infection. No uptake was visualized in the ilio-femoral bypass graft. At surgery, the infected vascular crossover prosthesis was removed and a reconstruction was performed using a saphenous vein patch. Blood cultures were obtained, and staphylococcus lugdunensis (coagulase-negative staphylococci commonly found in the inguinal area10) was found. The postoperative course was uneventful. Patient was discharged without complications and remains well 7 months later.
Fig. 1
Transversal CT image (A), and transversal (B), sagittal (C), and coronal (D) FDG-PET/CT fused images of a 57-year-old female showing an abnormal intense FDG uptake localized to the femoro-femoral crossover bypass graft. No uptake was visualized in the iliaco-femoral bypass graft.
Patient 2
A 55-year-old female with a medical history of diffuse peripheral atherosclerotic disease previously treated with an aorto-bifemoral bypass graft, presented with Fontaine stage IV intermittent claudication. A duplex and MR angiography showed a total occlusion of the right superficial femoral artery. The patient had a 6-mm ringed PTFE above knee right femoro-popliteal bypass, which was taken of the aorto-bifemoral graft.
Postoperatively, she developed an infection of the surgical wound in the right groin. The infected tissue was surgically removed, thereby exposing the proximal part of the femoro-popliteal bypass graft. Because of persistent fever, blood cultures were obtained and a Staphylococcus aureus was found. After a few days, leakage at the proximal anastomosis site was observed, indicating vascular graft infection. To differentiate whether the infected femoro-popliteal bypass graft was combined with an infection of the bifurcation prosthesis, a FDG-PET examination was performed.
The PET images showed an intense uptake of FDG, restricted to the femoro-popliteal bypass graft (Fig. 2). No uptake was visualized in the bifurcation prosthesis, excluding an infection. The infected vascular graft was surgically removed, staphylococcus aureus was cultured from the removed vascular prosthesis. The fever settled within two days. She remains well on follow-up one year later.
Fig. 2
Transversal (A), sagittal (B), and coronal (C) FDG-PET images of a 55-year-old female showing an intense uptake of FDG localized to the femoro-popliteal bypass graft. No uptake was visualized in the bifurcation prosthesis.
Discussion
Imaging plays a central role in the diagnosis of vascular graft infections. Accurate and prompt diagnosis of this complication is important for further management.
CT has been proposed as the gold standard in diagnosing vascular prosthetic infections. The presence of perigraft fluid, ectopic gas, perigraft soft tissue, and a persistent opacity have been described in vascular graft infection.3 However, perigraft fluid and inflammatory changes may persist for up to 3 months postoperatively, making an infection difficult to diagnose in the early post-operative phase. Labeled white cell scanning is highly sensitive, but lacks specificity. Suspected early graft infections often require surgical exploration for diagnosis.
In cases where an infection is suspected in patients with multiple prosthetic bypass grafts, the diagnosis is even more challenging. Single, or multiple vascular bypass grafts may be involved, which is important for surgical intervention. Recent publications confirmed the feasibility of using FDG-PET in diagnosing vascular prosthesis infection (Table 1).4, 5, 6, 7, 8, 9 However, none described its potential role to discriminate between infected and not infected vascular grafts within the same patient. This case report emphasizes the possibility of FDG-PET/CT to accurately localize the anatomic location of pathologic FDG accumulation in patients with multiple vascular grafts, thus discriminating between infected vascular prosthesis, or not.
Table 1. Overview of the literature considering FDG-PET and vascular graft infections
| Reference | Year | Type of study | Modality | No. of patients |
|---|---|---|---|---|
| Chacko et al.4 | 2003 | Retrospective cohort study | FDG-PET | 3 |
| Keidar et al.6 | 2003 | Case report | FDG-PET/CT | 1 |
| Krupnick et al.7 | 2003 | Case report | FDG-PET | 1 |
| Rohde et al.8 | 2004 | Case report | FDG-PET | 1 |
| Štádler et al.9 | 2004 | Case report | FDG-PET/CT | 1 |
| Fukuchi et al.5 | 2005 | Prospective cohort study | FDG-PET vs CT | 33 |
| Current study | 2006 | Case report | FDG-PET +FDG-PET/CT | 2 |
Although FDG accumulation indicates an elevated glucose metabolism, it is not specific for infection. A sterile inflammation like atherosclerosis, vasculitis, chronic polyartritis, or venous thrombosis may all cause false positive results, leading to unnecessary surgery and associated morbidity.11 However, Fukuchi et al. proposed that by using the characteristic uptake patterns of FDG as diagnostic criteria for infection, normal inflammatory reactions can accurately be distinguished from infection.5 The fusion of FDG-PET/CT combines the intensity and pattern of FDG uptake with reference to the corresponding images, thus playing a promising role in reducing false positive results.
In conclusion, FDG-PET is an imaging modality with various applications, including diagnosing a vascular graft infection. The hybrid FDG-PET/CT scan seems to be even more accurate and we expect it to play a significant role in the detection and management strategies of graft infection, especially in patients with multiple vascular bypass grafts. However today, its efficacy and additional value remains to be demonstrated by randomized clinical trials to reveal its place in the field of vascular surgery.
References
- Vascular graft infection: an analysis of sixty-two graft infections in 2411 consecutively implanted synthetic vascular grafts. Surgery. 1985;98(1):81–86
- . Diagnosis and management of infected prosthetic aortic grafts. Surgery. 1991;110(5):805–813
- . Aortoenteric fistula and perigraft infection: evaluation with CT. Radiology. 1990;175(1):157–162
- . Applications of fluorodeoxyglucose positron emission tomography in the diagnosis of infection. Nucl Med Commun. 2003;24(6):615–624
- Detection of aortic graft infection by fluorodeoxyglucose positron emission tomography: comparison with computed tomographic findings. J Vasc Surg. 2005;42(5):919–925
- . PET/CT using 2-deoxy-2-[18F]fluoro-D-glucose for the evaluation of suspected infected vascular graft. Mol Imaging Biol. 2003;5(1):23–25
- 18-fluorodeoxyglucose positron emission tomography as a novel imaging tool for the diagnosis of aortoenteric fistula and aortic graft infection–a case report. Vasc Endovascular Surg. 2003;37(5):363–366
- Recurrent Listeria monocytogenes aortic graft infection: confirmation of relapse by molecular subtyping. Diagn Microbiol Infect Dis. 2004;48(1):63–67
- . Diagnosis of vascular prosthesis infection with FDG-PET/CT. J Vasc Surg. 2004;40(6):1246–1247
- . Staphylococcus lugdunensis infections: high frequency of inguinal area carriage. J Clin Microbiol. 2003;41(4):1404–1409
- . 18-fluorodeoxyglucose positron emission tomographic imaging in the detection and monitoring of infection and inflammation. Semin Nucl Med. 2002;32(1):47–59
PII: S1533-3167(06)00091-4
doi:10.1016/j.ejvsextra.2006.11.003
© 2006 Published by Elsevier Inc.
Refers to article:
- FDG-PET and FDG-PET/CT for Diagnosing Infection in Patients with Multiple Vascular Bypass Grafts: A Report of Two Cases , 13 January 2007
