Congenital Renal Pathology • Renal agenesis/aplasia o Bilateral agenesis can be a part of oligohydramnios, pulmonary hypoplasia and extremity/facial anomalies o Potter’s syndrome is fatal within minutes to hours o Unilateral renal agenesis occurs 1 in 1000 births, accompanies by ureteral agenesis with absence of ipsilateral trigone and ureteral orifice. Compensatory hypertrophy of solitary kidney maintains normal renal function • Renal ectopia o Abnormal renal location, usually results when a kidney fails to ascend from its origin in the true pelvis; a rare exception occurs with a superiorly ascended (thoracic) kidney. o Pelvic ectopia increases the incidence of ureteropelvic junction obstruction, vesicoureteral reflux, and multicystic renal dysplasia. • Renal hypoplasia o Hypoplasia usually occurs because inadequate ureteral bud branching causes an underdeveloped, small kidney with histologically normal nephrons. If hypoplasia is segmental, hypertension can occur, and ablative surgery may be needed. • Renal dysplasia o The renal vasculature, tubules, collecting ducts, or drainage apparatus develops abnormally. o Diagnosis is by biopsy. o If dysplasia is segmental, treatment is often unnecessary. o If dysplasia is extensive, renal dysfunction may require renal replacement therapy. • Duplication o May involve the renal pelvis and ureters (accessory renal pelvis, double or triple pelvis and ureter), calyx, or ureteral orifice. o Duplex kidney, a single renal mass with > 1 collecting system, differs from a fused kidney, which involves fusion of 2 renal parenchymal masses o Some duplication anomalies have ureteral ectopy with or without ureterocele. • Fusion o Most common is horseshoe kidney    Occurs when renal parenchyma on each side is joined, usually at the lower renal poles An isthmus of renal parenchyma or fibrous tissue joins the kidneys at the midline The ureters course medially and anteriorly over this isthmus and usually function well o Crossed fused renal ectopia is the second most common fusion abnormality  The renal parenchyma of both kidneys are found on one side • Malrotation o Ureters cross the midline and enters the bladder on the contralateral side to the kidney