Aim: to improve the differential diagnosis of infected cysts in patients with ADPKD and to reduce false-positive rate of MR-urography.
Materials and methods: a total of 33 patients with ADPKD who underwent bilateral nephrectomy from 2015 to 2020 were included in the retrospective single-center study. In the group 1 (n=17) patients with histologically confirmed infected cyst (s) were included, while in the group 2 (n=16) there were patients without infected cysts. The frequency of symptoms (pain in the loin area, fever), the level of leukocytes in blood and urine, C-reactive protein (CRP) and the results of kidney MRI were compared.
Results. Pain, fever, leukocytosis, leukocyturia, and increased CRP levels were significantly associated with infected cysts. The sensitivity and specificity of MRI was 88.2% and 43.8%, respectively. The infected cysts were characterized by a significantly (p=0.004) lower value of the apparent diffusion coefficient (ADC): 0.67±0.21×10-3 mm2/s (95% confidence interval (CI) 0.56-0.79), versus 1.2±0.59×10-3 mm2/s (95% CI 0.89-1.5) in group 2. According to ROC analysis, the ADC value at the cut-off point was 0.83×10-3 mm2/s. The frequency of infected cysts during histological examination increased when the volume of the cyst was more than 13 ml. In multivariate analysis, only the CRP level was a reliable predictor of the presence of infected cysts. ROC analysis showed that the CRP level at the cut-off point was 83 mg/L (sensitivity 70.6%, specificity 75%).
Conclusion: In case of fever, pain in the loin area and high CRP level in patients with ADPKD, it is necessary to exclude infected cysts. MRI of the kidneys with the determination of the ADC level in cysts with limited diffusion on diffusion-weighted images is a highly informative method that allows to clarify the content of cysts.

Keywords: infected cyst, autosomal dominant polycystic kidney disease, end-stage renal disease, magnetic resonance imaging