Ureterovesical junction obstruction

Description

The metanephros (primitive kidney) appears in the 5th week of gestation developing from the metanephric diverticulum (ureteric bud) and the metanephric blastema. The ureteral bud increases in length, undergoing multiple divisions to form the ureters, renal pelvis, and related structures. Ureterovesical obstruction is due to a blockage at the level of the bladder and the ureter. The obstruction may be caused by stenosis of the ureteral valves but the most common cause is the failure of a narrow juxtavesical ureteral segment to dilate due to segmented fibrosis or localised absence of muscle. Developmental failure of that muscle may also cause failure of normal peristalsis. UVJ obstruction is more common in males than in females. It is the second most common cause of hydronephrosis in the fetus and newborn. It is also 2 to 3 times more common on the left side and bilateral in 15 to 25 percent.

Diagnosis

The diagnosis of UVJ depends upon the visualisation of megaureter. It may or may not be associated with a dilatation of the renal pelvis or calyces. A normal bladder is seen and the amniotic fluid volume is usually normal. It is important to differentiate between primary megaureter and a secondary or obstructive megaureter. Primary megaureter is the result of a defect in the development of ureteral structures at or above the level of the ureterovesical junction. In the secondary type, pressure from an external source such as a dilated vessel or tumour causes the dilation.

Differential Diagnosis

Vesicoureteric reflux (VUR) also presents with hydroureter and hydronephrosis and may be indistinguishable from UVJ obstruction. Dilated bowel usually contains particulate matter, is more anterior, and is not continuous with the renal pelvis. It is important to differentiate bilateral hydronephrosis-hydroureter from megacystic-microcolon-intestinal hypoperistalsis syndrome (MMIHS) and ureteral obstruction. This can be done on finding a normal size bladder and a normal amount of amniotic fluid in the former.

Sonographic Features

Hydronephrosis Hydroureter – can be tubular, tortuous, peristaltic Unilateral or bilateral

Normal bladder

Usually normal amniotic fluid volume in unilateral disease; may be oligohydramnios if bilateral

Renal pelvis may or may not be dilated

Associated Syndromes

  • none

References

Romero R, Pilon G, Jeanty P, Ghidini A, Hobbins J Urinary Tract and Adrenal Gland In: Prenatal Diagnosis of Congenital Anomalies. Appleton & Lange: Norwalk, p278 280
Stevenson R, Hall T, Goodman R Urinary Tract In: Human Malformations and Related Anomalies Vol II. Oxford U Press: New York, p501-516
Warkany J The Ureters In: Congenital Malformations, Notes and Comments. Year Book: Chicago, p1071
Crawfurd M díA In: The Genetics of Renal Tract Disorders Oxford U Press: Oxford, p572