How to recognize stent graft infection after endovascular aortic repair: the utility of 18F-FDG PET/CT in an infrequent but serious clinical setting

How to combine CTA, 99mTc-WBC SPECT/CT, and [18F]FDG PET/CT in patients with suspected abdominal vascular endograft infections?

PURPOSE

We aimed at comparing 99mTc-HMPAO white blood cells (99mTc-WBC) scintigraphy, 18fluorine-fluorodeoxyglucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) and CT angiography (CTA) in patients with suspected abdominal vascular graft or endograft infection (VGEI). Moreover, we attempted to define a new visual score for interpreting [18F]FDG PET/CT scans aiming at increasing its specificity.

METHODS

We prospectively compared 99mTc-WBC SPECT/CT, [18F]FDG PET/CT, and CTA in 26 patients with suspected abdominal VGEI. WBC scans were performed and interpreted according to EANM recommendations. [18F]FDG PET/CT studies were assessed with both qualitative (Sah's scale and new visual score) and semi-quantitative analyses. CTA images were interpreted according to MAGIC criteria. Microbiology, histopathology or a clinical follow-up of at least 24 months were used to achieve final diagnosis.

RESULTS

Eleven out of 26 patients were infected. [18F]FDG PET/CT showed 100% sensitivity and NPV, with both scoring systems, thus representing an efficient tool to rule out the infection. The use of a more detailed scoring system provided statistically higher specificity compared to the previous Sah's scale (p = 0.049). 99mTc-WBC SPECT/CT provided statistically higher specificity and PPV than [18F]FDG PET/CT, regardless the interpretation criteria used and it can be, therefore, used in early post-surgical phases or to confirm or rule out a PET/CT finding.

CONCLUSIONS

After CTA, patients with suspected late VGEI should perform a [18F]FDG PET/CT given its high sensitivity and NPV. However, given its lower specificity, positive results should be confirmed with 99mTc-WBC scintigraphy. The use of a more detailed scoring system reduces the number of 99mTc-WBC scans needed after [18F]FDG PET/CT. Nevertheless, in suspected infections within 4 months from surgery, 99mTc-WBC SPECT/CT should be performed as second exam, due to its high accuracy in differentiating sterile inflammation from infection.

Outcomes of Surgery for Endograft Infection in the Abdominal Aorta and Iliac Artery: A Nationwide Cohort Study

OBJECTIVE

This study aimed to clarify the clinical features, postoperative outcomes, and prognostic factors in patients with endograft infection in the abdominal aorta and iliac artery.

SUMMARY BACKGROUND DATA

Endograft infection in the abdominal aorta and iliac artery is a potentially fatal condition. However, due to its rarity, clinical characteristics and optimal treatment strategy remain to be established.

METHODS

In this nationwide retrospective cohort study, we investigated 112 patients who underwent surgical treatment for endograft infection in the abdominal aorta and/or iliac artery between 2011 and 2017 using a Japanese clinical registry. We examined the relationships between the preoperative and operative factors and the outcomes after surgery including persistent or recurrent infection related to the endograft and 90-day and 3-year mortality.

RESULTS

The median period between the index endograft placement and surgery for infection was 369.5 days. Persistent or recurrent endograft-related infection occurred in 34 patients (30.4%). The cumulative overall survival rates at 30 days, 90 days, 1 year, 3 years, and 5 years were 90.2%, 76.5%, 66.7%, 50.9%, and 31.5%, respectively. Partial removal or total preservation of the infected endograft was independently associated with short-term and late mortality. Preoperative anemia and imaging findings suggestive of fistula development to the gastrointestinal tract also showed an independent association with late mortality.

CONCLUSIONS

Surgical intervention for endograft infection in the abdominal aorta and iliac artery was associated with a high risk of postoperative morbidity and mortality. Total removal of the infected endograft should be attempted because partial removal or total preservation can lead to a poor prognosis.

[18F]FDG Uptake in Non-Infected Endovascular Grafts: A Retrospective Study

Purpose: After endovascular aneurysm repair (EVAR), an increased [¹⁸F]FDG uptake may be observed at PET/CT, being common to both vascular graft/endograft infection (VGEI) and sterile post-surgical inflammation. Increased non-specific metabolic activity, due to foreign body reaction, can persist for several years after surgery, thus complicating the interpretation of PET/CT studies. In this paper, we aimed to assess [¹⁸F]FDG distribution at different time-points after the implant of abdominal Endurant^® endografts in patients without suspicion of infection. Methods: We retrospectively evaluated [¹⁸F]FDG/CT in 16 oncological patients who underwent abdominal aortic aneurysm exclusion with Endurant^® grafts. Patients had no clinical suspicion of infection and were followed up for at least 24 months after scan. [¹⁸F]FDG PET/CT scans were interpreted using both visual and semi-quantitative analyses. Results: The time between the EVAR procedure and [¹⁸F]FDG PET/CT ranged between 1 and 36 months. All grafts showed mild and diffuse [¹⁸F]FDG uptake without a focal pattern. Mean values of SUVmax were 2.63 ± 0.48 (95% CI 2.38-2.88); for SUVmean 1.90 ± 0.33 (95% CI 1.72-2.08); for T/B ratios 1.43 ± 0.41 (95% CI 1.21-1.65). SUVmax and SUVmean were not correlated to the time elapsed from the procedure, but we observed a declining trend in T/B ratio over time. Conclusions: Endovascular implant of Endurant^® grafts does not cause a significant inflammatory reaction. The evidence of faint and diffuse [¹⁸F]FDG uptake along the graft can reliably exclude an infection, even in early post-procedural phases. Therefore, in patients with a low probability of VGEI, [¹⁸F]FDG PET/CT can also be performed immediately after EVAR.

Prosthetic vascular graft infection: A systematic review and meta-analysis on diagnostic accuracy of 18FDG PET/CT

INTRODUCTION

There is a high risk of mortality and morbidity associated with Vascular Graft Infections (VGI) which requires early diagnosis. The aim of the present systematic review and meta-analysis was to evaluate the diagnostic accuracy, sensitivity and specificity of 18FDG PET/CT in diagnosing VGI.

METHODS

A systematic review was conducted according to the PRISMA guidelines through a search in Embase, PubMed, and Cochrane databases. We evaluated five parameters including specificity, sensitivity, negative and positive predictive values (NPV and PPV), and accuracy. We used STATA/MP 15.0 (StataCorp, College Station, TX) for all of our analyses.

RESULTS

Overall 10 studies including 320 patients undergone 18FDG PET/CT were included. The sensitivity, specificity, positive and negative likelihood ratios along with their 95% CI were 0.92 (95% CI 0.88-0.95), 0.76 (95% CI 0.76-0.70), 3.49 (95% CI 3.49-2.32) and 0.14 (95% CI 0.09-0.23), respectively. The diagnostic odds ratio (DOR) for diagnosis of VGI was 37.12 (95% CI 14.84-92.82). The mean cut-off value of the maximum standardized uptake value (SUVmax) for diagnosis of VGI was 5.39 while the overall mean SUVmax among patients with VGI was 8.47.

CONCLUSION

According to our results, 18FDG PET/CT is a useful diagnostic method in detecting active VGI with high diagnostic accuracy. Because of its ability to evaluate morphology and main texture using SUVmax, the 18FDG PET/CT provides an objective assessment of aspects and extent of disease activity, which results in preventing unnecessary surgery, proper treatment planning, and evaluating the effectiveness of treatment.

Difficult diagnosis and management of a complicated Nellix graft infection

An 81-year-old man, with a complex vascular surgical history, presents with sepsis from an infected Nellix stent-graft. He required an urgent laparotomy, explantation of the graft, and extra-anatomical repair. Although now widely used for this indication, the preoperative 18F-fluorodeoxyglucose positron emission tomography/computed tomography was nondiagnostic for his stent-graft infection. We describe our management of a complicated Nellix graft infection and discuss the utility of positron emission tomography/computed tomography for stent-graft infections.

Case Report: 18F-FDG PET-CT for Diagnosing Prosthetic Device-Related Infection in an Infant With CHD

Patients who have undergone cardiac surgery using prosthetic devices have an increased risk of developing prosthetic device-related infection and mediastinitis. However, accurate diagnosis of prosthetic device-related infection can be difficult to evaluate and treat with antibiotic therapy alone. In recent years, ¹⁸F-fluorodeoxyglucose positron emission tomography-computed tomography (¹⁸F-FDG PET-CT) has made promising contributions to detect infective endocarditis, pacemaker infections, or other inflammations. Nevertheless, ¹⁸F-FDG PET-CT for congenital heart disease (CHD) with device infection has been sparsely reported. We present an infantile girl diagnosed with pulmonary atresia with a ventricular septal defect who underwent replacement of the right ventricle-to-pulmonary artery (RV-PA) conduit for improvement cyanosis. She developed high fever and was diagnosed with mediastinitis and bacteremia by Pseudomonas aeruginosa (P. aeruginosa) on postoperative day 4. Mediastinal drainage and 6 weeks of antibiotic therapy improved her condition, but bacteremia flared up on postoperative day 56. Despite a long course of antibiotic therapy, she had two more recurrences of bacteremia with the detection of P. aeruginosa. Echocardiography and chest contrast CT showed no evidence of vegetation and mediastinitis. On postoperative day 115, ¹⁸F-FDG PET-CT revealed an accumulation on the RV-PA conduit (SUV max 3.4). Finally, she developed an infectious ventricular pseudo-aneurysm on postoperative day 129 and underwent aneurysm removal and RV-PA conduit replacement on postoperative day 136. Our case showed the importance of ¹⁸F-FDG PET-CT for diagnosing specific localization of prosthetic device-related infection which is hard to detect using other imaging techniques. It can be a useful diagnostic tool for infantile patients with CHD with cardiac prosthetic devices and improve subsequent clinical treatments.

State of the art of 18F-FDG PET/CT application in inflammation and infection: a guide for image acquisition and interpretation

AIM

The diagnosis, severity and extent of a sterile inflammation or a septic infection could be challenging since there is not one single test able to achieve an accurate diagnosis. The clinical use of 18F-fluorodeoxyglucose ([¹⁸F]FDG) positron emission tomography/computed tomography (PET/CT) imaging in the assessment of inflammation and infection is increasing worldwide. The purpose of this paper is to achieve an Italian consensus document on [¹⁸F]FDG PET/CT or PET/MRI in inflammatory and infectious diseases, such as osteomyelitis (OM), prosthetic joint infections (PJI), infective endocarditis (IE), prosthetic valve endocarditis (PVE), cardiac implantable electronic device infections (CIEDI), systemic and cardiac sarcoidosis (SS/CS), diabetic foot (DF), fungal infections (FI), tuberculosis (TBC), fever and inflammation of unknown origin (FUO/IUO), pediatric infections (PI), inflammatory bowel diseases (IBD), spine infections (SI), vascular graft infections (VGI), large vessel vasculitis (LVV), retroperitoneal fibrosis (RF) and COVID-19 infections.

METHODS

In September 2020, the inflammatory and infectious diseases focus group (IIFG) of the Italian Association of Nuclear Medicine (AIMN) proposed to realize a procedural paper about the clinical applications of [¹⁸F]FDG PET/CT or PET/MRI in inflammatory and infectious diseases. The project was carried out thanks to the collaboration of 13 Italian nuclear medicine centers, with a consolidate experience in this field. With the endorsement of AIMN, IIFG contacted each center, and the pediatric diseases focus group (PDFC). IIFG provided for each team involved, a draft with essential information regarding the execution of [¹⁸F]FDG PET/CT or PET/MRI scan (i.e., indications, patient preparation, standard or specific acquisition modalities, interpretation criteria, reporting methods, pitfalls and artifacts), by limiting the literature research to the last 20 years. Moreover, some clinical cases were required from each center, to underline the teaching points. Time for the collection of each report was from October to December 2020.

RESULTS

Overall, we summarized 291 scientific papers and guidelines published between 1998 and 2021. Papers were divided in several sub-topics and summarized in the following paragraphs: clinical indications, image interpretation criteria, future perspectivess and new trends (for each single disease), while patient preparation, image acquisition, possible pitfalls and reporting modalities were described afterwards. Moreover, a specific section was dedicated to pediatric and PET/MRI indications. A collection of images was described for each indication.

CONCLUSIONS

Currently, [¹⁸F]FDG PET/CT in oncology is globally accepted and standardized in main diagnostic algorithms for neoplasms. In recent years, the ever-closer collaboration among different European associations has tried to overcome the absence of a standardization also in the field of inflammation and infections. The collaboration of several nuclear medicine centers with a long experience in this field, as well as among different AIMN focus groups represents a further attempt in this direction. We hope that this document will be the basis for a "common nuclear physicians' language" throughout all the country.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s40336-021-00445-w.

Climbing the steps of the evidence-based medicine pyramid: highlights from Annals of Nuclear Medicine 2019

We aimed to provide an overview on research path in nuclear medicine climbing the steps of the Evidence-Based Medicine (EBM) pyramid using review of 14 subjectively selected papers out of 111 published in the Annals of Nuclear Medicine during January-December 2019. Following the structure of the EBM hierarchy, we chose at least one study for each step of the pyramid from the basis (pre-clinical research, expert opinion, case report and case series), to the middle (case-control and cohort studies, randomised controlled trials), towards the top (meta-analyses and systematic reviews). Additionally, we collected information on the promoter of each included study: investigator-initiated trials (IITs) vs industry-sponsored trials (ISTs). We found that pre-clinical studies are primarily focused on the development of novel molecular targets in cancer, with promising results. At the same time, clinical investigations deal with cardiological, neurological, infectious and oncological applications using both SPECT and PET modalities. Additionally, radionuclide therapy gained interest and is experiencing comprehensive clinical implementation. Our overview confirms the current central role of IITs as compared with ISTs. Challenges and future directions in Nuclear Medicine research are discussed.

A systematic review and meta-analysis of 18F-fluoro-d-deoxyglucose positron emission tomography interpretation methods in vascular graft and endograft infection

OBJECTIVE

Vascular graft and endograft infection (VGEI) has high morbidity and mortality rates. Diagnosis is complicated because symptoms vary and can be nonspecific. A meta-analysis identified ¹⁸F-fluoro-d-deoxyglucose positron emission tomography-computed tomography (¹⁸F-FDG PET/CT) as the most valuable tool for diagnosis of VGEI and favorable to computed tomography as the current standard. However, the availability and varied use of several interpretation methods, without consensus on which interpretation method is best, complicate clinical use. The aim of this study was to evaluate the diagnostic performance of different interpretation methods of ¹⁸F-FDG PET/CT in diagnosis of VGEI.

METHODS

A systematic review was performed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. Data sources included PubMed/MEDLINE, Embase, and Cochrane Library. A meta-analysis was conducted on the different interpretation methods for ¹⁸F-FDG PET/CT in diagnosis of VGEI, including visual FDG uptake intensity, visual FDG uptake pattern, and quantitative maximum standardized uptake (SUVmax).

RESULTS

Of 613 articles, 13 were included (10 prospective and 3 retrospective articles). The FDG uptake pattern method (I² = 26.2%) showed negligible heterogeneity, whereas the FDG uptake intensity (I² = 42.2%) and SUVmax (I² = 42.1%) methods showed moderate heterogeneity. The pooled sensitivity for FDG uptake intensity was 0.90 (95% confidence interval [CI], 0.79-0.96); for uptake pattern, 0.94 (95% CI, 0.89-0.97); and for SUVmax, 0.95 (95% CI, 0.76-0.99). The pooled specificity for FDG uptake intensity was 0.59 (95% CI, 0.38-0.78); for FDG uptake pattern, 0.81 (95% CI, 0.71-0.88); and for SUVmax, 0.77 (95% CI, 0.63-0.87). The uptake pattern interpretation method demonstrated the best positive and negative post-test probability, 82% and 10%, respectively.

CONCLUSIONS

This meta-analysis identified the FDG uptake pattern as the most accurate assessment method of ¹⁸F-FDG PET/CT for diagnosis of VGEI. The optimal SUVmax cutoff, depending on the vendor, demonstrated strong sensitivity and moderate specificity.

Physiological Appearance of Hybrid FDG-Positron Emission Tomography/Computed Tomography Imaging Following Uncomplicated Endovascular Aneurysm Sealing Using the Nellix Endoprosthesis

Purpose: To investigate the physiological uptake of hybrid fluorine-18-fluorodeoxyglucose (FDG)-positron emission tomography/computed tomography (PET/CT) before and after an uncomplicated endovascular aneurysm sealing (EVAS) procedure as a possible tool to diagnose EVAS graft infection and differentiate from postimplantation syndrome. Materials and Methods: Eight consecutive male patients (median age 78 years) scheduled for elective EVAS were included in the prospective study (ClinicalTrials.gov identifier NCT02349100). FDG-PET/CT scans were performed in all patients before the procedure and 6 weeks after EVAS. The abdominal aorta was analyzed in 4 regions: suprarenal, infrarenal neck, aneurysm sac, and iliac. The following parameters were obtained for each region: standard uptake value (SUV), tissue to background ratio (TBR), and visual examination of FDG uptake to ascertain its distribution. Demographic data were obtained from medical files and scored based on reporting standards. Results: Visual examination showed no difference between pre- and postprocedure FDG uptake, which was homogenous. In the suprarenal region no significant pre- and postprocedure differences were observed for the SUV and TBR parameters. The infrarenal neck region showed a significant decrease in the SUV and no significant decrease in the TBR. The aneurysm sac and iliac regions both showed a significant decrease in SUV and TBR between the pre- and postprocedure scans. Conclusion: Physiological FDG uptake after EVAS was stable or decreased with regard to the preprocedure measurements. Future research is needed to assess the applicability and cutoff values of FDG-PET/CT scanning to detect endograft infection after EVAS.