PET/CT in therapy control of infective native aortic aneurysms

Abstract

Infective native aortic aneurysms (INAA) are aneurysms arising from infection of the aortic wall. Treatment is demanding with 5-year survival rates between 53 and 55%. The aim of our study was to evaluate the usefulness of ¹⁸F-fluorodeoxyglucose positron emission tomography/computed tomography (PET/CT) in the long-term monitoring of patients with proven INAA. Fifty-three PET/CT were performed in 15 patients with INAA in this single-center retrospective cohort study and retrospective analysis of prospectively collected Vascular Graft Cohort Study (VASGRA) data. Median metabolic activity (as measured by maximum standardized uptake value, SUVmax) of the aneurysms at the initial PET/CT was high (6.8 (IQR 5.7-21.8)), and lower at the last PET/CT prior to the end of antimicrobial therapy (3.9 (IQR 2.7-6.8); n = 11) as well as in the first PET/CT after the end of the treatment (3.9 (IQR 3.0-4.4);n = 6). Compared to the course of C-reactive protein alone, PET/CT provided different (> 20% difference in trend) or altering (opposed trend) information on the course of disease in at least 14 comparisons (56%) in 11 patients (73%). The one-year and five-year freedom from all-cause lethality was 92% (95% confidence interval 57%-99%). As compared to the course of C-reactive protein, PET/CT provides different and occasionally altering information in therapy control of INAA.

Figure 1

Courses over time of metabolic activity in PET/CT (SUVmax and SUVratio in the two graphs on the left) and CRP (graph on the right) in patients with proven infective native aortic aneurysms. Note: PET/CT provides additional or altering information (as defined in the methods section) on the course of disease in at least 14 comparisons (56%) in 11 patients (73%), as compared to CRP alone (i.e. patients: 02, 03, 04, 05, 06, 07, 08, 09, 11, 14, 15). Abbreviations: PET: positron emission tomography; SUV: standardized uptake value; CRP: C-reactive protein.

Figure 2

PET/CT of an 82-year old male patient (patient 05 in Tables 1, 2 and 3) with a vascular graft infection and spondylodiscitis due to Streptococcus agalactiae showed a new focal FDG uptake in the wall of the thoracic aorta in September 2017. Both readers rated the thoracic finding as a infective native aneurysm despite the fact that the vessel diameter was not pathologically widened. The first PET/CT follow-up in revealed a progression of the aneurysm in size with stable increased FDG uptake; at the same time the FDG uptake of the spondylodiscitis increased while it partially decreased in the vascular graft infection; C-reactive protein and white blood cell count decreased. After subsequent thoracic endovascular repair with an Endurant II Stent Graft Systems (MEDTRONIC), two further PET/CT follow-up, before and after termination of antimicrobial therapy (223 days of therapy) showed faint residual FDG uptake in all sites of infection. At the last clinical follow-up in January 2019 the patient was in good clinical condition with no sign of infection. Note: Panels A-D show maximum intensity reconstructions of PET; Panels E-P show fused PET/CT images. Abbreviations: PET: positron emission tomography; CT: computed tomography; FDG: 18F-fluorodeoxyglucose.

Figure 3

A 70-year old male patient (patient 04 in Tables 1, 2 and 3) presented with chest pain and signs for infection (C-reactive protein 122 mg/L). The initial PET/CT examination showed strongly increased FDG-uptake in the wall of an aortic arch aneurysm and no other infectious foci. Both PET/CT readers suspected a infective native aneurysm; which was clinically confirmed (Streptococcus agalactiae in blood cultures). At first PET/CT follow-up (ongoing antimicrobial therapy, after thoracic endovascular repair with a Conformable GORE TAG Thoracic Endoprosthesis and debranching) a strong residual focal FDG-uptake was detected adjacent to the graft, in line with a secondary vascular graft infection. The second PET/CT follow-up (ongoing antimicrobial therapy), showed only very faintly increased FDG-uptake adjacent to the graft. However, a new pneumonia in the right lower lobe was incidentally detected. The patient died 60 days after the last PET/CT due to a gastrointestinal bleeding not related to the thoracic infective native aortic aneurysm. Note: Panels A-C show maximum intensity reconstructions of PET; Panels D-I show fused PET/CT images. Abbreviations: PET: positron emission tomography; CT: computed tomography; FDG: 18F-fluorodeoxyglucose.