Introduction

Aortic prosthetic graft infection is a rare but serious complication. The resection area becomes very difficult to define if multiple prosthetic grafts are implanted or if the aorta is extensively replaced. We present a case of aortic graft infection after thoracoabdominal aortic aneurysm (TAAA) repair of Crawford extent II using FDG-PET/CT effectively.

Case

A 30-year-old man with Marfan syndrome was referred because of TAAA. This patient had undergone TAAA repair of Crawford extent II successfully. The intercostal arteries at the levels of Th8, Th9, Th10 and Th11 had been reattached by the graft interposition, and the visceral arteries were reattached using the island technique (Fig. 1). He developed high-grade fever of unknown origin 2, 4, and 8 years after TAAA repair, and had been treated with intravenous antibiotics at another hospital. This patient was transferred to our institution 9 years after TAAA repair with suspected aortic prosthetic graft infection due to presenting with pyrexia and blood cultures that were positive for Moraxella catarrhalis. Air around the mid-descending aorta was identified by CT (Fig. 1). A little fluid was seen near the celiac artery and the mid-descending aorta by CT. The level of C-reactive protein (CRP) was 1.93 mg/dL and the white blood cell count was 4400/μL.

Fig. 1
figure 1

After Crawford type II extension aneurysm repair. Preoperative computed tomography showed air around the mid-descending aorta (asterisk)

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Although intravenous antibiotics improved the pyrexia and returned to CRP level to normal within 4 weeks, the air around the mid-descending aortic graft persisted. High-uptake lesions on FDG-PET/CT were seen around the proximal anastomosis to the aortic arch (Fig. 2a), the mid-descending aortic graft (Fig. 2b), the abdominal aortic graft at the level of celiac artery (Fig. 2c) and the distal anastomosis to the terminal aorta (Fig. 2d). The maximal standardized uptake values (SUVmax) in these areas were 5.85, 4.43, 7.78 and 6.5, respectively.

Fig. 2
figure 2

Preoperative 18F-fluorodeoxyglucose positron emission tomography/computed tomography findings (sagittal plane). Proximal anastomosis (a), mid-descending aortic graft (b), abdominal aortic graft at the level of celiac artery (c), distal anastomosis (d)

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At surgery we dissected the prosthetic aortic grafts, particularly focusing on the high-uptake lesions detected by FDG-PET/CT. The abscess was localized around the mid-descending aortic graft (Fig. 3). We resected the mid-descending aortic graft, including the interposed grafts which were reattached to the intercostal arteries at the level of Th8, Th9, Th10 and Th11. After debridement, in situ graft re-replacement of the descending aorta and the reconstruction of the patent intercostal artery at the Th8 level with a rifampicin-bonded gelatin-impregnated Dacron graft and omentopexy were performed. Intraoperative microscopic study confirmed that the proximal and distal ends of the resected aortic graft were free of infection. The postoperative course was uneventful. Histopathological examination of the resected aortic graft revealed considerable neutrophil infiltration and no bacteria. Culture of resected aortic graft was negative. This patient remains free of recurrent infection at 3 months after surgery.

Fig. 3
figure 3

Localized abscess

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Discussion

Aortic prosthetic graft infection is associated with very high morbidity and mortality. Surgical treatment is essential, but very challenging in patients who are often critically ill. Although graft infection requires appropriate diagnosis, it is not easily obtained, as clinical signs are non-specific. The gold standard for diagnosing prosthetic graft infection has been CT. However, the major disadvantage of CT is that sensitivity decreases in the presence of low-grade prosthetic graft infection [1]. FDG-PET/CT has recently been used in the diagnosis of infectious disease. The standardized uptake value (SUV) is commonly applied as a relative measure of 18F-FDG uptake, in which areas of maximal focal 18F-FDG uptake are visually detected, and the SUVmax in each area is measured. Tokuda and colleagues [2] reported that FDG-PET/CT was useful to promptly and precisely confirm the presence of graft infection. They stated that SUVmax greater than 8 around a graft suggested the presence of graft infections (sensitivity 1.0 and specificity 0.8).

However, SUV is affected by factors such as physique, blood glucose level, renal function and the uptake duration between the injection and scan [3, 4]. The SUV is variable. To overestimate the SUV is very dangerous. Moreover, not only infection, but also various types of inflammation, can cause high uptake because FDG-PET/CT is based on the uptake of radio-active-labeled glucose in metabolically active cells. Keidar et al. [5] reported that 18F-FDG uptake was found in 92 % of noninfected vascular prostheses because of foreign body response, and the intensity of 18F-FDG uptake of prosthetic grafts did not change over time.

The role of CT in diagnosing vascular prosthetic graft infection has been widely investigated. Several characteristic features of vascular prosthetic graft infection with CT are perigraft air, fluid, and soft tissue attenuation, pseudoaneurysm, focal bowel thickening, and discontinuation of the aneurysmal wall [1]. When multiple prosthetic grafts were implanted or extended replacement of aorta was performed, it was impossible to determine the resection area only by CT. Moreover, it took a huge amount of effort to dissect all of the prosthetic grafts. However, resecting all of the infected grafts is mandatory [6]. In our case, we dissected the aortic graft efficiently by focusing on the high-uptake lesions on FDG-PET/CT. We finally determined resection areas based on the intraoperative findings and on intraoperative microscopic examination. Thus, FDG-PET/CT was useful as a tool for preparing the surgical strategy. Tissue culture of this patient was negative and this might have resulted from high doses of intravenous antibiotics before surgery.

Conclusions

We experienced a case of aortic graft infection after TAAA repair of Crawford extent II using FDG-PET/CT effectively. FDG-PET/CT is useful not only as a diagnostic modality but also as a tool for selecting optimal surgical strategy.