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Renal Obstruction Anomalies Upper Renal Tract (Kidneys & Ureters)

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    Renal tract     dilation and     hyronephephrosis
      Upper renal       tract obst.
      Lower renal       tract obst.
    Multicystic     dysplastic kidney
    Polycystic kidney
    Renal agenesis


Introduction Antenatal Postnatal West Midlands Data



Blockages of the renal/urinary tract can be physical, where there is a narrowing or obstruction to the flow of urine, or functional, where the tubes are open (patent) but are not working properly to propel the urine along.

Obstruction of the pelvi-ureteric junction (PUJ)

PUJ obstruction is functional stenosis at the junction between the renal pelvis and ureter and is the most common cause of hydronephrosis. PUJ occurs sporadically and is usually functional, where the PUJ is patent, rather than due to a physical obstruction but may be due to ureteral valves.

Most cases of PUJ obstruction are unilateral (80%), the prognosis is good, and most cases can be managed conservatively. In cases of bilateral PUJ obstruction, the degree of obstruction may vary between sides. In severe cases, the kidney may dilate to form an abdominal cyst. This cyst can obstruct the intestine and lungs causing polyhydramnios.
On ultrasound examination hydronephrosis is present but the ureters and bladder are not dilated and the volume of amniotic fluid is normal. Dilated renal pelves are seen with or without calyceal dilatation. Serial scans should be performed to monitor any pelvicalyceal dilatation and amniotic volume.


Ureterocele is the congenital cystic dilation of the terminal ureter. Ureterocele may be simple (functional) or ectopic. In cases of simple ureterocele, the ureteric orifice in the bladder wall is normally situated but the VUJ is obstructed and the ureter dilated at the orifice.
Ectopic ureterocele is a more complex anomaly often associated with ectopic ureters and ureteral duplications. The cystic part of the intramural segment of the ureter bulges around the bladder wall and the ureter extremity is ectopic, often situated at the bladder neck or urethra.

Obstruction of the urinary flow by a ureterocele is usually accompanied by dilatation ureter and hydronephrosis. Surgical removal is possible.

Obstruction of the uretero-vesicle junction (UVJ)

Anomalies of the uretero-vesicle junction are the second most common cause of hydronephrosis. Distal obstruction of the ureter is usually functional but less frequently may be due to ureteral atresia or stricture. On ultrasound a normal ureter cannot be seen, so any ureter seen is dilated. UVJ obstruction usually causes a mild degree of hydronephrosis and hydroureter, the bladder is normal in size and not hypertrophic. Unlike cases of megaureter where the ureter is straight, obstruction of the UVJ can make the ureter serpiginous (snake-like). The prognosis of an isolated anomaly is usually good.

Primary vesicoureteral reflux (VUR)

Vesicoureteral reflux is the retrograde flow of urine up the ureter from bladder to kidney. Distal obstruction of the ureter is usually functional. Primary VUR can occur due to a shortening of a narrow segment (intramural segment) of the ureter when passing though the bladder wall, reducing the ratio of the length and diameter of this section, causing a failure in the transmission of the normal peristaltic waves.

On ultrasound, this anomaly should be suspected when intermittent dilatation of upper urinary tract is seen. It frequently results in mild hydronephrosis and mild dilatation of pelvis and ureter, liquor volume may be unaffected.

Twenty percent of cases are familial in origin, and VUJ is a common finding in children with urinary tract infection. Many cases resolve spontaneously in childhood although long-term outcomes depend on the extent of renal growth failure and reflux nephropathy (scarring).

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Complete obstruction early in fetal life causes renal hypoplasia and dysplasia. Intermittent obstruction may allow normal renal development. Obstruction in later pregnancy will result in hydronephrosis and the severity of renal impairment depends on the degree and duration of obstruction.

It is important to delay postnatal assessment until 48 hours as mild to moderate hydronephrosis may be present in the first day of life due to dehydration. Postnatal renal function assessed by serial isotope imaging, or pyeloplasty.

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© Perinatal Institute 2011