The Use of a Visual 4-point Scoring Scale Improves the Yield of 18 F-FDG PET-CT Imaging in the Diagnosis of Renal and Hepatic Cyst Infection in Patients With Autosomal Dominant Polycystic Kidney Disease

Purpose [18F]FDG PET/CT (PET/CT) proved useful in the diagnosis of renal and hepatic cyst infection (CyI) in patients with autosomal dominant polycystic kidney disease (ADPKD). However, the definition of CyI by PET/CT is unclear. Here, we characterize the [18F]FDG uptake in CyI in order to infer a visual 4-point diagnostic scale. Methods All ADPKD patients hospitalized between 2007 and 2019 for suspected CyI and who underwent an [18F]FDG PET/CT scan were listed. CyI was defined by 5 concomitant criteria: fever ≥ 38 °C; abdominal pain; peak plasma CRP ≥ 70 mg/L; no other cause of inflammation; and favorable outcomes after antibiotics for ≥ 21 days. First, all PET/CT images were visually interpreted. Next, the [18F]FDG uptake around the suspected CyI was scored using a semiquantitative 4-point scale in comparison to blood and liver activities. Results Sixty [18F]FDG PET/CT scans were performed for suspected CyI in 38 ADPKD patients. Twenty-nine episodes met the gold-standard criteria for CyI. The visual assessment of PET/CT images reached a sensitivity of 73.1% and a specificity of 70.6%. Using the 4-point scale, an [18F]FDG score ≥ 3 (i.e., cyst uptake > liver) improved the specificity to 85.3%. Conclusion [18F]FDG PET-CT is helpful in CyI diagnosis in ADPKD, and the use of a 4-point scoring of [18F]FDG uptake improves its diagnostic yield, with positive and negative predictive values of 78.3 and 78.4%, respectively. External validation is required.