Abstract
The 18F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDG-PET/CT) offers an excellent negative predictive value. Consequently, it is a reliable tool for excluding an infectious phenomenon in case of negativity. In case of persistent fever of unknown origin after cardiac surgery and in combination with other bacteriological examinations and medical imaging, we can rely on FDG-PET/CT to confirm or eliminate deep infections and prosthetic endocarditis. For this reason, FDG-PET/CT should be considered among the examinations to be performed in case of suspected infection after cardiac surgery. We have reported the case of a 76-year-old man who presented with a fever of unknown origin and recurrent septic shocks after a biological Bentall procedure combined with left anterior descending (LAD) coronary artery revascularization by the left internal thoracic artery. We performed a FDG-PET/CT which showed external iliac vein and right common femoral vein hyperfixation with infiltration of adjacent soft tissues, highly suspected to be an infectious process.
Learning objective
The aim of this case report is to show that FDG-PET/CT, in combination with other bacteriological examinations and medical imaging, can be extremely helpful in detecting deep infectious sources, even during the early postoperative period.
Keywords: Positron emission tomography, Computed tomography, Surgery complications, Aortic root replacement
Introduction
The 18F-fluorodeoxyglucose positron emission tomography combined with computed tomography (FDG-PET/CT) has become an essential imaging method in oncology. There is a growing interest in its use to detect and monitor infectious and inflammatory processes [1]. As a result, it has a promising role in the diagnosis and management of unknown origin sepsis [2]. Its excellent negative predictive value allows an almost complete exclusion of an infectious phenomenon. The FDG-PET/CT seems to be an interesting diagnostic tool for the confirmation or elimination of deep infections and/or prosthetic endocarditis [1] in febrile patients after cardiac surgery.
Case history
An obese, dyslipidemic 76-year-old male patient presented with chronic atrial fibrillation (AF). The patient was already known for aortic valve stenosis since 2006 and had been suffering from increasing dyspnea over several months. We found he had severe aortic regurgitation, a left anterior descending (LAD) coronary artery stenosis, and a 67 mm aneurysm of the ascending aorta.
He underwent a biological Bentall procedure (complete aortic-root replacement by a valvular bioprosthesis sutured inside a Dacron vascular graft) and LAD coronary artery revascularization by the left internal thoracic artery.
During surgery, after weaning from cardiopulmonary bypass, the patient had an anaphylactic shock soon after blood and fresh frozen plasma transfusion. The anaphylactic shock was postoperatively proven by allergy testing and successfully treated with adrenaline.
The postoperative course was marked by a basal right pneumonia on day 5. The patient was initially treated with a combination of levofloxacin, amoxicillin and clavulanic acid, with preserved hematosis. All arterial and venous catheters were changed, in accordance with our intensive care unit (ICU) recommendations. A new central venous catheter was placed in the patient’s right femoral vein.
Six days after surgery, pneumonia was complicated by a septic shock caused by Klebsiella oxytoca and Proteus mirabilis. Inotropic and vasopressor agents were requested.
Nine days after surgery, the patient presented with a new septic event consisting of chills, fever and vasoplegia. Blood cultures became positive for Staphylococcus aureus.
Ten days after surgery, a change of antibiotics was made to imipenem and cilastatin, and vancomycin and levofloxacin. Fifteen days after surgery, another septic shock required volemic replacement, the reintroduction of amines, the introduction of caspofungin, and amikacin in bolus over two days. Sixteen days after surgery, blood cultures on different catheters gave a positive result for Klebsiella oxytoca.
Given the repeated septic discharges, despite appropriate antibiotic therapy, a thoraco-abdominal CT-scan was performed, showing no deep infections and an uncomplicated aortic hematoma, usually found in patients who have undergone aortic surgery (See Fig. 1).
Figure 1.
Thoracic CT: periaortic hematoma (A), minimal bilateral pleural effusion (B).
Twenty-five days after surgery, while the patient was apyretic over a period of 48 h with a low level of procalcitonin (PCT: 1.2 ng/ml), the antibiotic treatment was reduced to vancomycin alone. Three days later, a new septic discharge occurred during a transesophageal echocardiography (TEE). Once again, blood cultures were positive for the same kind of staphylococcus aureus previously isolated.
The patient was subsequently placed on a wide-spectrum antibiotic therapy of rifampicin, imipenem, cilastatin, sulfamethoxazole, trimethoprim and levofloxacin.
Given the repeated septicaemia despite antibiogram adapted antibiotic therapy, a FDG-PET/CT was performed. It revealed a moderate sternal uptake, as expected after a sternotomy, and a source of pulmonary uptake due to the pneumonia responsible for the initial hypoxia. In addition, it detected right external iliac vein and common femoral vein fixation, with infiltration of adjacent soft tissues. This source was suspected as having caused the infectious process. There were no signs of infection around the vascular prosthesis (See Figs. 2 and 3).
Figure 2.
Right external iliac vein hyperfixation and no abnormal chest hyperfixation (FDG-PET/CT).
Figure 3.
Right external iliac vein and right common femoral vein hyperfixation with infiltration of adjacent soft tissues (FDG-PET/CT).
The catheters were changed and the right femoral catheter removed. Antibiotic therapy was once again modified (piperacillin/tazobactam, fluconazole, sulfamethoxazole, trimethoprim) and intravenous heparin was started. Thus, the hypothesis of a vascular prosthesis infection was excluded. The patient presented a good clinical response without further complications under appropriate antibiotic treatment, and after the removal and replacement of infected catheters.
Discussion
The aim of this case report is to show that FDG-PET/CT may be proposed for the detection of deep infections, even during the early postoperative period, and in combination with other bacteriological examinations and medical imaging [1]. Many prospective studies have been published on the use and value of FDG-PET/CT for the diagnosis of infectious diseases. In 1998, Sugawara et al. assessed the feasibility of FDG-PET/CT for early detection of human infection, and established the diagnosis of the presence or absence of active infection in 10 out of 11 patients [3]. In a study on 24 patients, Ichiya et al. reported a sensitivity of 92% (23/25) for the detection of various lesions. The overall sensitivity of FDG-PET/CT in detecting infectious lesions seemed high. The negative predictive value of the technique was between 90 and 100% [4,5]. In a recent prospective study on 33 patients with suspected arterial graft infection, Fukuchi et al. showed the superiority of FDG-PET/CT compared with CT (sensitivity, 91% versus 64%, PPV 91% versus 70%, VPN 95% versus 83%) [6].
Some authors suggest waiting for a period of six to eight weeks after surgery before the completion of the PET–CT, as perioperative inflammation can generate a parasite diffused hyperfixation which can make the interpretation of the test more difficult [1]. Chacko et al. conducted 169 FDG-PET/CT to reveal 175 sites of infection and most of the lesions involved were localized in the bone or were prosthetic infections [7]. All these studies supported our choice to perform a FDG-PET/CT for our patient. In particular, FDG-PET/CT may be helpful in the prompt detection and treatment of prosthetic infections, and in the reduction of the high morbidity and mortality rates usually related to this pathology. Nonetheless, we still need to define a precise indication and time for its use.
Cardiac surgery postoperative fever is common and requires a planned approach [8,9,10]. We recommend following the management guidelines of catheter-related bloodstream infection as described by David et al. [11].
It is debatable whether venous catheterization of the femoral vein is associated with an increased risk of infectious complications compared with catheterization of the subclavian vein. Femoral catheterization is associated with a higher incidence rate of overall infectious complications (19.8% vs 4.5%; P < .001; incidence density of 20 vs 3.7 per 1000 catheter-days) as well as major infectious complications (clinical sepsis with or without bloodstream infection, 4.4% vs 1.5%; P = .07; incidence density of 4.5 vs 1.2 per 1000 catheter-days) [12]. A randomized trial found that subclavian venous catheterization was associated with a significantly lower rate of total infectious complications than femoral venous catheterization and a trend toward a lower rate of suspected or confirmed catheter-related bloodstream infections (1.2 infections per 1000 catheter-days vs 4.5 infections per 1000 with femoral catheterization; P = 0.07) [12].
In addition, we experienced an unsupportive communicative environment between cardiac surgeons and the intensive care unit (ICU) team. The intensivists believed that the origin of the fever was surgical and were unwilling to respect our ICU guidelines to change the central venous catheters as soon as possible in case of postoperative fever. Clear and fast communication is essential to good clinical outcomes and good outcomes are the result of effective team work.
Conclusion
FDG-PET/CT is a multimodal emerging technology which is extremely useful in detecting deep infections in case of diagnostic uncertainty after cardiac surgery.
Authors’ contributions
Djamel Adjtoutah: Drafting the article and revising it for critically important intellectual contents.
Alaa Azhari: Drafting the article and revising it for critically important intellectual contents.
Youcef Larabi: Patient management and data acquisition.
Enrica Dorigo: patient management and data acquisition.
Charles Merlin: Patient management, data acquisition and interpretation.
Xavier Marcaggi: Head of the Cardiology Department and final approval of the submitted version.
Armel Simplice Nana: analysis and interpretation of data.
Lionel Camilleri: Head of heart surgery department and final approval of the submitted version.
Kasra Azarnoush: Concept and design of the study and its final approval.
Footnotes
Peer review under responsibility of King Saud University.
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