[Case of infected renal cyst in polycystic kidney disease].

A 56-year-old woman with polycystic kidney disease (PKD) presented with high fever and left back pain. Abdominal computed tomography (CT) scan showed multiple renal cysts, left hydronephrosis and a left ureteral stone. Her condition could not be managed with antibiotic therapy and indwelling left ureteral stent. Infected of left renal cysts was suspected, we performed diffusion-weighted magnetic resonance imaging (MRI). Diffusion-weighted MRI showed higher signal intensity in one renal cyst than in other renal cysts. CT-guided percutaneous puncture of an infected cyst was performed. Her symptoms and fever resolved following the procedure. Identification of an infected renal cyst in PKD is often difficult on either ultrasonography or CT. Diffusion-weighted MRI allowed exact localization of the infected cyst among many cysts in PKD.