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Articles » Magnetic Resonance Imaging » MRI, Urinary tract
2005-11-15-15 MRI, hydronephrosis © Werner


 Heron Werner, MD*, Pedro Daltro, MD*, Dorothy Bulas, MD #

* Heron Werner, MD & Pedro Daltro, MD*
Clínica de Diagnóstico por Imagem (CDPI) & Instituto Fernandes Figueira (IFF) – FIOCRUZ
Rio de Janeiro – Brazil

# Dorothy I. Bulas M.D.
Professor of Radiology and Pediatrics
Children"s National Medical Center
George Washington University Medical Center
111 Michigan Ave, NW,   Washington D.C. 20010

Hydronephrosis is characterized by the dilatation of calices and renal pelvis. It can be obstructive or not. Hydronephrosis has an incidence of 10-50:10,000 births and is responsible for 75 percent of fetal renal abnormalities of intrauterine detection. The most frequent cause of obstructive hydronephrosis is the stenosis of the ureteropelvic junction, being bilateral in between 10 to 15 percent of cases (Nyberg, 1990). The imaging study will vary in accordance with the degree of obstruction at the pyeloureteral junction. A proper diagnosis requires the dilatation of calices, and, most importantly, renal pelvis, without dilatation of the corresponding ureter.

Mild hydronephrosis of intrauterine detection tend greatly towards regression throughout the first months of life. The regression is still possible with hydronephrosis of moderate degree, but with a lower incidence. On the other hand, more severe hydronephrosis need an immediate postnatal evaluation, so as to determine the necessity or not for shunt. The recourse to lead shunt must be taken in consideration, in the severe cases, still during the gestation period. An association with other malformations is around 20 percent. An unfavorable diagnosis is expected when there is oligohydramnios.

When there is ureterohydronephrosis, the most frequent cause is the vesicoureteral reflux, also known as vesicoureteral regurgitation, which can be unilateral or bilateral. The severity of reflux is determined by the degree of urethral distention as well as by the pyelocalyceal systems, being possible to use the internationally accepted grading method.

When the cause of ureterohydronephrosis is obstructive, it is necessary to consider four possibilities of diagnosis:

  • stenosis of the ureterovesical junction;
  • ureterocele;
  • urethral ectopia;
  • non obstruction mega ureter and no reflux.

Excepting ureterocele, all other causes will require a postnatal study so that one may produce a final diagnosis.

When ureterohydronephrosis affects only part of the kidney, the necessary diagnosis will be that of complete pyeloureteral duplication. It is necessary to observe the following:

  • duplication with dilation of the upper pole: the cause must be obstruct and is in most cases due to ureterocele, which is a congenital dilation of the intramucosal segment of the distal ureter. That congenital dilation is frequent in duplicated systems but not in single ones. It is also necessary to consider the possibility that the dilation is a question of either stenosis of the pyeloureteral junction or even urethral ectopia.
  • duplication with dilation of the lower pole: the cause is always because of vesicoureteral reflux.




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