Hydronephrosis in children: degrees, causes, diagnosis and treatment

What is hydronephrosis?

Hydronephrosis consists of dilatation of the renal pelvis and calyces. It can be unilateral or bilateral, depending on whether one or both kidneys are affected. When the ureter is also dilated we speak of ureterohydronephrosis.

Thanks to prenatal ultrasound its diagnosis is more and more frequent, but a renal ultrasound should be performed after approximately one week of life to confirm the diagnosis. Depending on the dilatation and the existence of atrophy of the renal parenchyma, hydronephrosis is classified in different degrees. Hydronephrosis may be transient, i.e. it may disappear during pregnancy, at birth or in the first months of life, or it may be the cause of uropathy requiring treatment. Obviously, the lesser the dilatation, the more likely it is to resolve spontaneously.

What causes hydronephrosis?

Hydronephrosis can result from a lack of maturation of the urinary tract, and in these cases it usually disappears. This maintained dilatation can affect renal function and therefore should be monitored and sometimes treated surgically. Other times hydronephrosis is the cause of an obstruction at some point in the urinary tract, a reflux of urine into the ureter, poor bladder function or an alteration of the urethra.

Pyeloureteral junction stenosis is the most common obstruction and is located at the junction between the renal pelvis and the ureter.

How is it diagnosed?

Hydronephrosis is detected by ultrasound. This can give us a lot of information such as which part of the urinary tract is dilated, the aspect of the renal cortex, if there are bladder alterations or if there are other associated anomalies.

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Once the ultrasound data have been analyzed, it may be necessary to perform nuclear medicine studies to rule out obstruction and obtain an assessment of renal function. When we want to rule out a ureteral vesicle reflux, a sonocystography or conventional cystography should be performed, which consists of introducing a contrast agent into the bladder and observing whether it ascends towards the kidneys. In some cases it is necessary to complete the study with other imaging studies such as a uroMRI to clarify certain anatomical aspects.

What does the treatment consist of?

Lower degrees of hydronephrosis usually resolve spontaneously. Sometimes expectant management is decided, based on the patient’s clinical and renal function, and in other cases treatment is directly surgical. A decrease in renal function or the presence of urinary tract infections are signs that indicate that surgical treatment may be necessary. The type of treatment will depend on the pathology causing the hydronephrosis.

The treatment of pyeloureteral junction stenosis consists of resection of the stenotic area and its subsequent reconstruction. Laparoscopic surgery allows its repair, leaving minimal scars and with a faster recovery of the child. The obstructive megaureter is caused by a malfunction of the fibers that facilitate the movement of urine into the bladder in the final zone of the ureter, at the entrance to the bladder. Although the initial treatment is usually conservative, sometimes it requires endoscopic dilation of the injured area and even surgical repair with laparoscopic surgery. Low grade ureteral vesic reflux usually resolves without intervention, but in high grade cases with urinary tract infections, endoscopic correction is indicated. The important thing is to establish the cause of hydronephrosis and with a correct diagnosis act accordingly. We also recommend close follow-up in those patients in whom expectant management is decided, in order to detect any change in the degree of hydronephrosis or any alteration of renal function and modify our attitude if necessary.