Hydronephrosis results from dilation or stretching of the inside of the kidney, called the renal pelvis or "collecting system.” The main function of the urinary tract is to remove waste and fluid from the body. The urine is formed when the kidneys filter blood and remove excess waste materials and fluid. The urine is made in the solid outer part of the kidney called the cortex.
Urine collects into the renal pelvis. From the renal pelvis, the urine travels down a narrow tube called the ureter into the bladder. The bladder slowly fills up with urine, which empties from the body through another small tube called the urethra.
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, due to slow drainage or obstruction somewhere between the renal pelvis that is the junction of the kidney and ureter entry into the bladder called the ureterovesical junction. 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, many of which do not cause any harm to the kidneys; but in some cases, hydronephrosis can be associated with poorly functioning kidneys. 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 or graded based on a scale of 1 to 4 (4 being severe) by the society of fetal urology (SFU). The cause of this narrowing is not currently known but probably develops when the kidneys are forming around eight to ten weeks of gestational life.
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.
Prenatal hydronephrosis is a condition that involves one or both of the baby’s kidneys and can be seen on a routine ultrasound during pregnancy. The hydronephrosis will be safely monitored throughout pregnancy with ultrasounds. Some babies have hydronephrosis for only a short time and then goes away naturally. If the hydronephrosis did not go away before birth, your baby will need tests and possibly treatment after birth depending on the severity of the condition.
At Comer Children’s, the pediatric urologist will examine all options before performing surgery for hydronephrosis.
In children with mild hydronephrosis (grades 1 to 2), it is safe to carefully monitor these children. This is called observational therapy, and typically, the problems correct themselves as the child grows. Observational therapy involves closely watching your child's health and kidney growth through clinical features, ultrasound, and close observation for urinary tract infection (UTI). Since urinary tract infections can cause permanent damage to the kidneys, it might be recommended that your child takes daily low dose (prophylactic) antibiotics to prevent infection. Studies have demonstrated that babies with high-grade hydronephrosis (grades 3 to 4) receiving antibiotic prophylaxis have a significantly lower rate of UTI when compared to untreated children. Your pediatric urology team will discuss the risks and benefits of antibiotic prophylaxis based on your individual child’s needs.
In some cases, your pediatric urologist will recommend a test called a voiding cystourethrogram (VCUG). Additional testing is important because diagnosing and treating a potential abnormality early can prevent urinary tract infections and permanent kidney damage or scarring. A VCUG provides important information about the shape and size of your child's bladder, the bladder neck or opening, and the tubes that drain the urine from the kidneys into the bladder, called ureters. It is used to diagnose reflux, the abnormal backflow of urine from the bladder into the ureter and up to the kidney. It also provides anatomic information about the urethra (the tube that takes the urine from the bladder outside the body) to make sure there's no blockage, a condition called posterior urethral valves.
Some conditions causing hydronephrosis will need to be corrected with surgery.
Pyeloplasty is the surgical reconstruction of the renal pelvis to drain and decompress the kidney. The goal of the surgery is to relieve a uretero-pelvic junction (UPJ) obstruction. Pyeloplasty may be performed open or robotically. During open surgery, a 2-3 inch cut is made just below the ribs. The obstructed segment of ureter is removed. The normal caliber ureter is then reattached to the renal pelvis. A stent (a tiny wire-meshed tube) is placed to drain urine from the kidney. After the surgery heals, the stent will be removed. During robotic surgery, the same type of repair is performed, but through a minimally invasive approach. The surgeon will make two to three small (1/4 to 1/2 inch) incisions in the abdominal skin. Surgeons at Comer Children’s are highly experienced in both open and minimally invasive surgery for children.
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