Ureteropelvic Junction Obstruction vs. Multicystic Kidney (Aplastic Cystic Kidney)
Left picture: In this schoolgirl a congenital pyeloureteral junction obstruction is present with a grotesque hydronephrosis (subpelvic ureteral stenosis); notice the constriction of the proximal ureter. The operative preparation feigns a relatively fair amount of normal renal tissue; but, in reality, the renal pelvis inside of the kidney is more dilated than visible from the outside, thereby pretending a persistent fetal lobulation. Right picture: This female toddler has a multicystic kidney. Renal parenchyma is hardly visible, and the proximal ureter is not present at all. Not the multicystic kidney is the cause of the repeated urinary tract infections, but additional anomalies of the contralateral kidney or of the ipsilateral residual distal ureter, which is ending cranially for different distance from the bladder; in this case a reflux in the residual ureter was present; it had to be removed in the same session as the kidney.
Left picture: View of the back side of the right kidney of a 9-year-old girl, which has been removed due to recurrent urinary tract infections, and a quota of less than 10 % of the total function of both kidneys. The renal pelvis has a cystic dilatation. Right picture: Operative preparation of a nearly 4-year-old girl with recurrent urinary tract infections. It includes a kidney which is barely recognizable as such, with at least three cystic cavities and possible hilar structures.