title: The relevance of 18F-fluorodeoxyglucose positron emission tomography/computed tomography imaging in diagnosing prosthetic graft infections post cardiac and proximal thoracic aortic surgery.
abstract: OBJECTIVE
  Diagnosis of prosthetic graft infection after cardiac and proximal aortic surgery is a challenge. Besides technical considerations, redo surgery is associated with substantial morbidity and mortality. Therefore, an accurate diagnosis is mandatory. We report on our experience with hybrid 18-fluorodeoxyglucose positron emission tomography ((18)F-FDG PET)/computed tomography (CT) imaging, which is increasingly used to diagnose infections in the detection of graft infection after cardiac surgery.
  
  
  METHODS
  Twenty-six patients who underwent (18)F-FDG PET/CT imaging after cardiac surgery between February 2010 and September 2014 for suspected graft infection were retrospectively analysed (81% male, age 54.3 ± 13.7 years). PET/CT imaging was performed 36.5 ± 70.5 (0.5-300) months after surgery. 2 patients (8%) had undergone aortic valve replacement (concomitant ascending and proximal arch replacement in 1), 1 (4%) aortic root reconstruction, 9 (35%) aortic root replacement (concomitant partial arch in 4, arch replacement and postoperative TEVAR in 1), 2 (8%) ascending aortic and partial arch replacement and 2 (8%) ascending aortic replacement along with frozen elephant trunk. In 10 (38%), more than one previous cardiac surgical procedure had been performed. Maximum standardized uptake values (SUVmax) were obtained for all patients. If the patients were reoperated on, the final diagnosis was derived from intraoperative findings and/or microbiological results. Otherwise, the longest clinical follow-up available served as a reference.
  
  
  RESULTS
  Conventional CT was positive for infection in 13 cases (50%). In 22 (85%), PET was indicative of infection (SUVmax 10.5 ± 4.1). PET did not only confirm true-positive CT results in all but 1 case; in almost 30%, it provided substantial additional diagnostic information in comparison with CT alone. Receiver operating characteristic analysis identified an SUVmax of 7.25 to achieve maximum sensitivity (89%) and specificity (100%) in prediction of infection. Twelve patients (46%) required redo surgery for graft infection; in 1 additional patient (4%), sternal re-fixation was necessary. Furthermore, 2 patients had to be reoperated on for torn-out anastomosis and paraprosthetic perfusion (8%).
  
  
  CONCLUSIONS
  PET provides functional data, confirms a CT diagnosis and may even increase diagnostic sensitivity in comparison with CT alone in selected cases. Specificity can be compromised by postoperative changes or chronic inflammatory reactions induced by the graft. CT and/or echocardiography should remain the first diagnostic step in case of a suspected infection because of their broad and fast availability. If confirmation is needed or diagnosis is not achievable using conventional methods, PET might be chosen as the next modality to gain additional information in experienced centres.
authors.affiliation: Department of Cardiac Surgery, University Hospital Munich, Ludwig-Maximilian-University, Munich, Germany sabina.guenther@med.uni-muenchen.de.
authors.forename: Sabina P W
authors.initials: SP
authors.lastname: Guenther
authors.affiliation: Institute of Clinical Radiology, University Hospital Munich, Ludwig-Maximilian-University, Munich, Germany.
authors.forename: Clemens C
authors.initials: CC
authors.lastname: Cyran
authors.affiliation: Department of Nuclear Medicine, University Hospital Munich, Ludwig-Maximilian-University, Munich, Germany.
authors.forename: Axel
authors.initials: A
authors.lastname: Rominger
authors.affiliation: Institute of Clinical Radiology, University Hospital Munich, Ludwig-Maximilian-University, Munich, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Saam
authors.affiliation: Institute of Clinical Radiology, University Hospital Munich, Ludwig-Maximilian-University, Munich, Germany.
authors.forename: Philipp M
authors.initials: PM
authors.lastname: Kazmierzcak
authors.affiliation: Department of Cardiac Surgery, University Hospital Munich, Ludwig-Maximilian-University, Munich, Germany.
authors.forename: Erik
authors.initials: E
authors.lastname: Bagaev
authors.affiliation: Department of Cardiac Surgery, University Hospital Munich, Ludwig-Maximilian-University, Munich, Germany.
authors.forename: Maximilian
authors.initials: M
authors.lastname: Pichlmaier
authors.affiliation: Department of Cardiac Surgery, University Hospital Munich, Ludwig-Maximilian-University, Munich, Germany.
authors.forename: Christian
authors.initials: C
authors.lastname: Hagl
authors.affiliation: Department of Cardiac Surgery, University Hospital Munich, Ludwig-Maximilian-University, Munich, Germany.
authors.forename: Nawid
authors.initials: N
authors.lastname: Khaladj
mesh_terms: D000328:Adult; D000368:Aged; D001011:Aorta / Q000601:surgery; D001021:Aortic Valve / Q000382:microbiology; D001807:Blood Vessel Prosthesis / Q000382:microbiology; D019917:Blood Vessel Prosthesis Implantation / Q000009:adverse effects; D005260:Female; D019788:Fluorodeoxyglucose F18; D019918:Heart Valve Prosthesis Implantation / Q000009:adverse effects; D006801:Humans; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D016459:Prosthesis-Related Infections / Q000175:diagnosis* / Q000209:etiology; D019275:Radiopharmaceuticals; D012189:Retrospective Studies; D019616:Thoracic Surgical Procedures / Q000009:adverse effects*; D014057:Tomography, X-Ray Computed
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
keywords: 18F-FDG PET/CT imaging; Cardiac surgery; Graft infection; Proximal thoracic aortic surgery