Autosomal dominant polycystic kidney disease (ADPKD) is prone to multiple complications, including cyst infection (CyI). [18F]-FDG PET/CT imaging proved useful in the diagnosis of renal and hepatic CyI. A 4-point scale comparing the uptake of [18F]-FDG in the suspected infected cyst versus the hepatic physiological background has been proposed. We performed an independent validation of this semi-quantitative scoring system.

All ADPDK patients hospitalized between January 2009 and November 2019 who underwent an [18F]-FDG PET/CT for suspected CyI were retrospectively identified using computer-based databases. Medical files were systematically reviewed.

CyI was conventionally defined by the combination of fever (>38°C), abdominal pain, increased plasma CRP levels (≥70mg/L), absence of any other cause of inflammation, and favorable outcome after≥21 days of antibiotics. [18F]-FDG uptake of the suspected CyI was evaluated using a 4-point scale comparing the uptake of [18F]-FDG around the infected cysts to the uptake in the hepatic parenchyma. Statistics were performed using SAS version 9.4.

Fifty-one [18F]-FDG PET/CT scans in 51 patients were included, of which 11 cases of CyI. The agreement between the 4-point scale and the gold-standard criteria of CyI was significant, with an odds ratio of 6.03 for CyI in case of a score≥3 (P 0.014). The corresponding sensitivity and specificity of [18F]-FDG PET/CT using the 4-point scale were 63.6% and 77.5%, respectively.

Our independent validation cohort confirms the use of a semi-quantitative 4-point scoring system of [18F]-FDG PET/CT imaging in the diagnosis of CyI in patients with ADPKD.