Hounsfield unit attenuation value can distinguish pyonephrosis from hydronephrosis in parents with upper urinary tract stones

Abstract Objective: To evaluate the attenuation value [Hounsfield unit (HU)] in non-contrast CT for distinguishing pyonephrosis from hydronephrosis in parents with upper urinary tract (UTS) stones and to identify factors predicting the development of sepsis in patients with pyonephrosis. Methods: Between October 2019 and October 2021, patients with hydronephrosis or pyonephrosis secondary to upper urinary tract stones (UTS) were retrospectively searched in our study. All patients with UTS were treated with either percutaneous nephrostomy (PCN) or surgical management (percutaneous nephrolithotomy / transurethral ureteroscope lithotripsy). We excluded patients treated with extracorporeal shock-wave lithotripsy or patients with bilateral upper urinary tract stones. Patients whose CT was not performed in our hospital or treated in another hospital were also excluded. Clinical data regarding basic information, clinical feature, co-morbidities, previous intervention, infection-related indicators, Calculi-related indicators, HU values of the renal pelvis, the thick wall of the renal pelvis on CT were collected. Univariate and multivariate logistic analyses were performed. ROC curves were drawn to predict pyonephrosis and sepsis. Results: Two-hundred-forty patients with UTS were included in our study, 191 patients had hydronephrosis without pyonephrosis (Group 1), and 49 patients had hydronephrosis with pyonephrosis (Group 2). The HU value of the renal collecting system in Group 2 (mean, 15.46; range, +1/+30) was significantly higher than that in Group 1 (mean, 5.5;5 range -6/+24) (P = 0.02); the ROC curve analysis revealed that the HU value (AUC = 0.613) of 9.5 was the best cut-off value to predict calculi-related obstructive pyonephrosis, with 71.4% sensitivity and 70.2% specificity. But it cannot predict the development of sepsis in patients with postoperative pyonephrosis (p = 0.11). Multivariate analysis showed that age (P = 0.041), sex (p = 0.036), herpes labialis (p = 0.018), and serum albumin (p = 0.027) were significant predictors for the development of sepsis in patients with postoperative pyonephrosis. Conclusions: The HU attenuation value of the renal collecting system can distinguish pyonephrosis from hydronephrosis, but it cannot predict sepsis in patients with pyonephrosis postoperative. Older, low-serum albumin female patients with renal pyonephrosis caused by UUT stones are more likely to develop urogenic sepsis.