Hydronephrosis [water - kidney condition] refers to a kidney with a dilated pelvis and collecting system. It can be caused by obstruction of the ureters or bladder outlet. Hydronephrosis can also result from reflux (retrograde leakage of urine from the bladder up the ureters to the renal pelvis. Rarely, some children have hydronephrosis without either obstruction or reflux. This is thought to result form abnormal smooth muscles of the renal pelvis or ureter causing ectasia.
This longitudinal ultrasound of a left kidney shows a large hypoechoic area (black on an ultrasound means no echoes) in the center of the kidney. Notice how the dilation extends into the parenchyma. These areas are the calyces of the kidney. The normal hyperechoic area in the center of the kidney (the hilum) is replaced by a large hydronephrotic renal pelvis. This kidney has hydronephrosis due to obstruction of the upper ureter (additional studies revealed the location of the obstruction).
|This longitudinal ultrasound shows a kidney with less severe hydronephrosis. The parenchyma is relatively normal in thickness. The dilation of the collecting system extends from the renal pelvis to the calyces. This is a grade III hydronephrosis.|
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©David A. Hatch, M.D., 1996