Hydronephrosis results from dilation or stretching of the inside of the kidney. This part of the kidney is called the "collecting system" because the urine made in the solid outer part of the kidney collects in the funnel-shaped kidney pelvis and then drains down the ureters to the bladder.
Normally, the urine drains so well from the kidney to the bladder that no urine is visible in the kidney on ultrasound studies. Hydronephrosis is the term used to describe the extra urine seen in the kidney. Sometimes, the urine dilates both the kidney and the ureter resulting in a condition called hydroureternephrosis.
Hydronephrosis has not been linked to anything parents may have done during pregnancy, but it can be hereditary. Usually, these abnormalities are seen during the mother's prenatal ultrasound evaluation. In some cases, however, hydronephrosis may not be recognized until after birth or later in childhood.
Causes of Hydronephrosis
We know that there are several causes of hydronephrosis. Often, it results from a narrowing at the point where the ureter leaves the kidney. This condition is called ureteropelvic junction obstruction (UPJ obstruction). The hydronephrosis depends on the extent of the blockage and the amount of stretching of the kidney. Hydronephrosis ranges from mild to moderate to severe. The cause of this narrowing is not currently known but probably develops before the fourth month of pregnancy.
Hydronephrosis can also be caused when a reflux or the backward flow of urine from the bladder back up into the ureters and kidneys. This condition may be hereditary and is a common cause of serious urinary tract infections in children.
Blockage at the lower end of the ureter is another cause of hydronephrosis and hydroureter. The ureter may enter the bladder in an abnormal area or may be covered with a thin membrane that prevents the drainage of urine into the bladder. The exact cause of the obstruction may not be known until special tests are performed.
At Comer Children’s, the pediatric urologist will examine all options before performing surgery for hydronephrosis. In children with mild hydronephrosis or reflux, it is safe to carefully monitor these children. This is called observational therapy. Observational therapy involves closely watching your child's health and kidney growth while your child takes low dose antibiotics to prevent infection. Typically, the problems correct themselves as the child grows.
Some conditions causing hydronephrosis will need to be corrected with surgery. In some cases, the pediatric urologist will operate through a small telescope placed into your baby’s bladder while the baby is still very young. Early relief of an obstruction in the bladder or ureter will allow your baby’s urinary tract to heal and develop normally.