[Malrotated kidney causing prenatal giant hydronephrosis]

We report the case of a malrotated right kidney associated with giant prenatal hydronephrosis due to a non vascular extrinsic ureteropelvic compression. The kidney presented an hyper-rotation of 180° in relation to the original fetal position, with the renal hilum backward looking. At neonatal surgery we discover that the inferior pole of the kidney pushes laterally the ureteropelvic junction like a violin bridge. The simple uncrossing of the ureteropelvic junction from the inferior renal pole relieves the extrinsic ureteral obstacle and the giant hydronephrosis. The authors summarize the morphogenesis of the upper urinary tract which allowed to understand this rare anatomical variation.