Obstructive uropathy
Section snippets
Antenatal detection of hydronephrosis
More infants are diagnosed with antenatal hydronephrosis as the result of routine second trimester ultrasound screening. The current incidence of antenatal hydronephrosis is 1 : 100 to 1 : 500 [1]. There is no agreement on the normal fetal renal pelvis diameter (RPD); however, most studies consider a RPD of greater than 5 mm to be abnormal [2], [3]. The likelihood of renal pathology depends upon the severity of the hydronephrosis [2]. VUR is the most likely diagnosis in cases of mild hydronephrosis
Multicystic dysplastic kidney
With an incidence of 1 in 4300 live births, MCDK is the second most common etiology of an abdominal mass in the neonate [8]. The pathogenesis of MCDK is poorly understood but appears to be the result of failed coordination of the branching ureteric bud and developing metanephros, possibly the result of ureteric obstruction [9]. Several genes have been implicated in the development of cysts in MCDK. These include PAX2, BCL2, IGF-II, and IGF binding protein. PAX2 is expressed in tubules with
UPJ obstruction
UPJ obstruction is the most common cause of hydronephrosis detected in utero with an incidence of 1 in 2000 [2], [30]. There is a male to female ratio of 3 : 1, and the obstruction is bilateral in 20–25% of cases [2]. The etiology of UPJ obstruction may include intrinsic stenosis or valves, insertion anomaly of the ureters, peripelvic fibrosis, or crossing vessels. Dilatation of the renal pelvis and collecting system with no evidence of ureteral dilatation along with a normal bladder is
UVJ obstruction
UVJ obstruction has a male to female ratio of 4 : 1, is bilateral in 25% of patients, and is more common in the left ureters. Ultrasound examination shows ureteral dilatation (megaureter) and a dilated renal pelvis. UVJ obstruction is associated with an aperistaltic segment of the distal ureter at the UVJ. Conservative management is preferred by some urologists [31], [32]. Surgical treatment consists of excision of the distal ureteric segment, tapering of the ureter, and reimplantation or
Animal models of obstruction
There are multiple animal models used to investigate obstructive uropathy. The two most common are the fetal sheep and the neonatal rat. The fetal sheep is commonly used for the ease in performing fetal surgery. Fetal sheep studies with ureteral ligation and contralateral nephrectomy early in gestation show severe hydronephrosis and dysplasia [38], [39]. If ureteral ligation is performed late in gestation, simple hydronephrosis occurs [38]. Studies suggest there is some reversal of renal
Extrarenal manifestations of obstructive uropathy
The kidneys are responsible for the production of 90% of the amniotic fluid after 20 weeks gestation; therefore, severe intrauterine urinary obstruction can lead to oligohydramnios [37]. Since amniotic fluid is crucial for normal lung and orthopedic/soft tissue development, these systems may show marked compromise in the setting of antenatal urinary obstruction and oligohydramnios. Respiratory complications can range from mild to severe lung hypoplasia [23], [37], and respiratory insufficiency
Clinical manifestations/complications/management
Infants with severe obstructive uropathy are prone to electrolyte and fluid balance abnormalities. Sodium wasting is observed secondary to decreased Na absorption in cortical collecting tubules, in part due to decreased Na/K ATPase activity [30]. Patients will often require sodium supplementation. Additional electrolyte abnormalities are characterized by hyperkalemia and metabolic acidosis. A type IV RTA often develops with impaired distal tubular potassium and hydrogen ion secretion [30]. This
Conclusion
Many infants are now being diagnosed with antenatal hydronephrosis on routine second trimester ultrasound screening. Postnatal evaluation is indicated if the renal pelvic diameter is greater than 5 mm. Urinary obstruction can cause renal tubular damage resulting in sodium and water wasting as well as decreased nephron endowment. Severe renal injury may eventually require renal replacement therapy. Future studies are warranted to investigate therapies to halt renal damage in obstructive uropathy.
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