Reflux nephropathy, which also is called chronic nonobstructive pyelonephritis, is defined as reflux of urine from the urinary bladder through an incompetent vesicoureteral junction and into the ureter and pyelocaliceal system and, eventually, into the renal parenchyma, without mechanical obstruction of the urine outflow tract.
The kidney with obstructive nephropathy shows diffuse thinning of the renal parenchyma of variable degrees (sometimes to a few millimeters), loss of corticomedullary junction landmark, blunting or loss of renal papillae, and dilatation of the pyelocaliceal system (hydronephrosis) and thickening of its wall (Figure 2, A).
In milder cases only a portion of the renal parenchyma is scarred, and only the corresponding portion of the pyelocaliceal system is dilated and thickened, with the rest of the kidney being normal or even showing some compensatory hypertrophy (Figure 3).
15,18) The pyelocaliceal changes are an integral element of the lesion.
Duplex system can be described as the kidney with two pyelocaliceal systems, with either single ureter or bifid ureter (partial ureteral duplication) or double ureter draining separately into the urinary bladder (complete ureteral duplication).
2,5] Unilateral complete ureteral duplication with a single renal parenchyma drained by 2 pyelocaliceal systems is even more rare.