**2. Epidemiology of congenital obstructive nephropathy**

Congenital obstructive nephropathy is the most common cause of CKD in children and is among the top three etiologies of pediatric end-stage renal disease (ESRD; NAPRTCS, 2009).

Congenital Obstructive Nephropathy: Clinical Perspectives and Animal Models 5

1991). UVJ obstruction is four times more common in males and arises more often on the left, with bilateral obstructions occurring in up to 25% of cases (Gimpel et al., 2010; Woodward & Frank, 2002). Like UPJ obstruction, UVJ obstruction is typically associated

Fig. 1. Radiological findings associated with UPJ obstruction in an 18 month old female. Left

hydronephrosis was detected prenatally, and the patient had normal postnatal renal function with no vesicoureteral reflux (VUR). She was managed conservatively, with gradual improvement in hydronephrosis on serial imaging studies through age 15 months. However, at 18 months of age hydronephrosis worsened. **A - C.** Ultrasound of urinary bladder (A), right (B) and left (C) kidneys. The bladder (A) is normal in conformation with normal wall thickness, and no hydroureter is seen. The right kidney (B) is structurally normal with slight pelviectasis. The left kidney (C) demonstrates marked hydronephrosis with blunted calyces and thinned parenchyma, which had worsened from previous findings of moderate but improving hydronephrosis. **D and E.** Technetium-99m MAG3 diuretic renal scan using the F+20 protocol confirmed a left ureteropelvic junction obstruction. Sequential posterior images of the abdomen and pelvis (D) are grouped into perfusion, parenchymal, and excretion phases. Ten milligrams of furosemide were administered 20 minutes after tracer injection. With injection of the tracer, there is bolus visualization of the inferior vena

with an adynamic ureteric segment that fails to propagate effective urine flow.

Congenital obstructive nephropathy is often grouped with renal agenesis, hypoplasia/dysplasia and other abnormalities as a heterogeneous entity termed *congenital anomalies of the kidney and urinary tract* (CAKUT). CAKUT is relatively common, affecting up to 2% of pregnancies (Ismaili et al., 2003; Wiesel et al., 2005). CAKUT accounts for 51% of childhood CKD in North America (NAPRTCS, 2009), and similar frequencies in registry data from around the world (Neild, 2009a). Among the diagnoses within the broad category of CAKUT, obstructive disease carries the greatest risk for developing ESRD (Sanna-Cherchi et al., 2009). The association of renal hypodysplasia and impaired glomerular filtration rate with urological obstruction is well-established. More subtle renal changes such as hypertension, impaired sodium/water handling, and acidosis are also common (Farnham et al., 2005; Gillenwater et al., 1975). Thus the full clinical impact of congenital obstructive nephropathy is immense.
