Radiological and surgical correlation of pelviureteric junction obstruction in positional anomalies of the kidney in children

Pelviureteric junction obstruction, also known as ureteropelvic junction obstruction, is a congenital narrowing of the urinary excretory tract at the junction between the renal pelvis and the ureter and is a common cause of congenital pelvicalyceal dilatation. The outcome is variable, from spontaneous resolution to renal parenchymal function loss in cases of untreated high-grade obstruction. Abnormalities in renal ascent, rotation and vascularity can be associated with pelviureteric junction obstruction and easily overlooked radiologically. In this pictorial review, we explore the anatomical, radiological and surgical correlations of pelviureteric junction obstruction in the context of a normal kidney and a spectrum of renal abnormalities, including hyper-rotation (also known as renal malrotation), failed renal ascent, fusion anomalies and accessory crossing renal vessels. For each scenario, we provide technical tips on how to identify the altered anatomy at the first ultrasound assessment and correlation with scintigraphic, cross-sectional and postoperative imaging where appropriate. A detailed ultrasound protocol specifically to assess and characterise pelviureteric junction obstruction in paediatric patients is also offered.