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The urinary tract is a common location for congenital anomalies of varying significance. Many anomalies are asymptomatic and diagnosed via prenatal ultrasonography or part of a routine evaluation for other congenital anomalies. Other anomalies are diagnosed secondary to obstruction, infection, or trauma.
Bilateral renal agenesis as part of a syndrome of oligohydramnios, pulmonary hypoplasia, and extremity and facial anomalies (classic Potter syndrome) is fatal within minutes to hours. Fetal demise is common.
Unilateral renal agenesis is not uncommon and accounts for about 5% of renal anomalies. Many cases result from complete involution in utero of a multicystic dysplastic kidney. It usually is accompanied by ureteral agenesis with absence of the ipsilateral trigone and ureteral orifice. However, the ipsilateral adrenal gland is unaffected. No treatment is necessary; compensatory hypertrophy of the solitary kidney maintains normal renal function. Because the kidneys share a common embryologic origin with the vas deferens and uterus, boys may have agenesis of the vas deferens and girls may have uterine anomalies.
Incidence of autosomal recessive polycystic kidney disease is about 1/10,000 to 1/20,000 births. Autosomal dominant polycystic kidney disease is much more common, occurring in about 1/500 to 1/1000 live births (see Autosomal Dominant Polycystic Kidney Disease (ADPKD)).
Autosomal recessive disease affects
Kidneys are usually greatly enlarged and contain small cysts; renal failure is common in childhood.
The liver is enlarged and has periportal fibrosis, bile duct proliferation, and scattered cysts; the remainder of the hepatic parenchyma is normal. Fibrosis causes portal hypertension by age 5 to 10 yr, but hepatic function is normal or minimally impaired.
Disease severity and progression vary. Severe disease may manifest prenatally or soon after birth or in early childhood with renal-related symptoms; less severely affected patients present in late childhood or adolescence with hepatic-related symptoms.
Affected neonates have a protuberant abdomen with huge, firm, smooth, symmetric kidneys. Severely affected neonates commonly have pulmonary hypoplasia secondary to the in utero effects of renal dysfunction and oligohydramnios.
In patients aged 5 to 10 yr, signs of portal hypertension, such as esophageal and gastric varices and hypersplenism, occur. If the patient presents in adolescence, nephromegaly is less marked, renal insufficiency may be mild to moderate, and the major symptoms are those related to portal hypertension.
Diagnosis may be difficult, especially without a family history. Ultrasonography may show renal or hepatic cysts; definitive diagnosis may require biopsy. Ultrasonography in late pregnancy usually allows presumptive in utero diagnosis. If needed, molecular testing for PKHD1 can be done when clinical criteria is not met.
Many neonates die in the first few days or weeks of life from pulmonary insufficiency. Most who survive develop progressive renal failure often requiring renal replacement therapy. Experience with renal transplantation with or without hepatic transplantation is limited. When transplantation is done, hypersplenism must be controlled (see page Hypersplenism) to obviate difficulty with hypersplenism-induced leukopenia, which increases the risk of systemic infection. Portal hypertension may be treated by portacaval or splenorenal shunts, which reduce morbidity but not mortality.
Supernumerary collecting systems may be unilateral or bilateral and may involve the renal pelvis and ureters (accessory renal pelvis, double or triple pelvis and ureter), calyx, or ureteral orifice. Duplex kidneys have a single renal unit with more than one collecting system. This anomaly differs from fused kidneys, which involves fusion of two renal parenchymal units maintaining their respective individual collecting systems. Some duplication anomalies have ureteral ectopy with or without ureterocele and/or vesicoureteral reflux (VUR). Management depends on the anatomy and function of each separately drained segment. Surgery may be necessary to correct obstruction or VUR.
With fusion anomalies, the kidneys are joined, but the ureters enter the bladder on each side. These anomalies increase the risk of ureteropelvic junction obstruction, vesicoureteral reflux, congenital renal cystic dysplasia (see page Congenital Renal Cystic Dysplasia), and injury caused by anterior abdominal trauma.
Horseshoe kidney, the most common fusion anomaly, occurs when renal parenchyma on each side of the vertebral column is joined at the corresponding (usually lower) poles; an isthmus of renal parenchyma or fibrous tissue joins at the midline. The ureters course medially and anteriorly over this isthmus and generally drain well. Obstruction, if present, is usually secondary to insertion of the ureters high in the renal pelvis. Pyeloplasty relieves the obstruction and can be done without resecting the isthmus.
Crossed fused renal ectopia is the 2nd most common fusion anomaly. The renal parenchyma (representing both kidneys) is on one side of the vertebral column. One of the ureters crosses the midline and enters the bladder on the side opposite the fused kidneys. When ureteropelvic junction obstruction is present, pyeloplasty is the treatment of choice.
Fused pelvic kidney (pancake kidney) is much less common. A single pelvic kidney is served by two collecting systems and ureters. If obstruction is present, reconstruction is needed.
In this condition, there is a nonfunctioning renal unit consisting of noncommunicating cysts with intervening solid tissue composed of fibrosis, primitive tubules, and foci of cartilage. Usually, ureteral atresia is also present. The contralateral kidney is usually normal, but up to 10% of patients may have VUR or ureteropelvic junction obstruction. Frequently, the kidney progressively involutes and eventually is no longer visible on ultrasonography. Development of tumors, infection, and/or hypertension is rare. Most experts recommend observation unless solid tissue is extensive or unusual-appearing on ultrasonography, or there is progressive cystic enlargement, in which case the kidney may be removed.
In renal dysplasia (a histologic diagnosis), the renal vasculature, tubules, collecting ducts, or drainage apparatus develops abnormally. Diagnosis is by biopsy. If dysplasia is segmental, treatment is often unnecessary. If dysplasia is extensive, renal dysfunction may necessitate nephrologic care, including renal replacement therapy.
Renal ectopia (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. Pelvic ectopia increases the incidence of ureteropelvic junction obstruction, VUR, and multicystic renal dysplasia. Obstruction and severe reflux may be corrected surgically when indicated (if causing hypertension, recurrent infections, or renal growth retardation).
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