**3. Classification of congenital obstructive nephropathy**

The timing, extent, etiology, and location of impaired urine flow are important considerations in describing and classifying the causes of obstructive nephropathy. One of the most important and useful distinctions is the anatomic level at which the obstruction occurs – namely, the upper urinary tract (kidney or ureter) versus the lower urinary tract (bladder, bladder outlet or urethra). Upper urinary tract lesions have little potential to affect the contralateral kidney, whereas lower tract anomalies generally put both kidneys at risk.

#### **3.1 Upper urinary tract obstructions**

Congenital obstructions of the upper urinary tract include ureteropelvic junction (UPJ) and ureterovesical junction (UVJ) obstructions, as well as obstructing ureteroceles and other anomalies of ureteric structure or position.
