How is hydronephrosis differentiated from Wilms tumor on imaging?

Updated: Mar 04, 2019
  • Author: Ali Nawaz Khan, MBBS, FRCS, FRCP, FRCR; Chief Editor: Eugene C Lin, MD  more...
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The renal collecting system forms a part of the central echogenic complex, and it is frequently not identifiable as a separate structure. Visualization of the collecting system depends on the rate of urine formation and drainage. Slight dilatation of the collecting system is a common normal finding during diuresis or when the bladder is full. In these cases, the dilatation resolves when the bladder is emptied.

Hydronephrosis is simply dilatation of the renal collecting system. This is not always due to obstruction, and in the converse, obstruction does not always cause hydronephrosis. Hydronephrosis is seen as anechoic fluid in the renal collecting system and pelvis separating the echoes of the central sinus. In long-standing cases, images may show secondary thinning of the renal parenchyma. Dilated calyces lose their sharp, angular margins and become blunted.

When hydronephrosis is considerable, the entire collecting system is outlined as a series of connected fluid-filled channels. When part of the renal collecting system is dilated, the condition may superficially resemble a Wilms tumor on sonographic examination, but close inspection can easily differentiate the 2 conditions.

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