Hydronephrosis occurs when urine backs up inside the renal pelvis, an area of the kidney.
The kidneys are two large bean-shaped organs located in the mid-back, just below the rib cage. They filter waste products from the blood and excrete them from the body in the form of urine.
Urine is stored in a part of the kidney called the renal pelvis and then flows down the ureters, two thin tubes that connect the kidney to the bladder. From the bladder, urine leaves the body through a tube called the urethra.
Hydronephrosis is a distention of a renal pelvis due to a backup of urine. The most common cause of hydronephrosis is ureteropelvic junction (UPJ) obstruction, a blockage at the point where the renal pelvis joins the ureter. Hydronephrosis may also be ca used by vesicoureteral reflux, a backflow of urine from the bladder.
Other causes include megaureter, ureterocele, ectopic ureter, and bladder disorders such as posterior urethral valves, neurogenic bladder, or congenital bladder outlet obstruction due to urethral stricture.
Hydronephrosis is typically diagnosed before birth in a prenatal ultrasound. It also may be suspected in a child who experiences a urinary tract infection or abdominal pain.
The most important diagnostic test is the ultrasound. This can show how dilated the kidney is, whether both kidneys are involved, and whether the ureter is also dilated or the bladder is distended.
Additionally, the ultrasound can give valuable information about the appearance of the functioning part of the kidney.
The diagnosis of reflux is made using an x-ray called a voiding cystourethrogram (VCUG). A urinary catheter (tube) is placed into the child's bladder and fills the bladder with x-ray dye. During urination, the path of the dye is followed. If it goes up toward the kidneys, reflux is diagnosed.
UPJ obstruction is often confirmed with a test called diuretic renal scan (DRS). A tiny amount of weak radioactive material is injected into a vein. A scanner follows the tracer's progress through the urinary system. If all or most of the tracer remains in th e kidney and does not wash out in the urine, blockage is diagnosed.
Treatment is required only when kidney function is impaired or the kidney becomes greatly enlarged. The underlying cause of hydronephrosis determines the course of treatment.
Most cases of vesicoureteral reflux are treated with daily antibiotic therapy. In cases where surgery is recommended, the operation is highly successful and carries relatively little risk.
For severe UPJ obstruction, surgery is usually required. The operation to correct UPJ obstruction is called a pyeloplasty. Usually this surgery is performed through an incision in the side.
With recent advances in minimally invasive surgical techniques, pediatric urologists can correct UPJ obstruction without the need for open surgery. The new technique provides significant benefits in reduced postoperative pain, faster recovery, and minimal sca rs.
In one such procedure, called laparascopic pyeloplasty, a laparascope (a slim tube with a tiny video camera mounted on the end) is inserted into a small incision in the navel. While watching the procedure on a TV monitor, the surgeon inserts instruments throu gh other small incisions to repair the obstruction.
The blocked part of the ureter is removed and the healthy ureter reconnected to the kidney. A temporary tube called a stent may be placed inside the ureter to drain the kidney until surgery heals.
Currently, this operation is being used in older children and adults, although eventually it will be applicable to toddlers or even infants. The hospital stay for either open or laparoscopic pyeloplasty is usually only one to three days.
The success rate is generally 95 percent for all open operations, and appears to be similar for the laparoscopic operation.
Long-term follow-up is recommended for hydronephrosis, regardless of treatment type. Periodic ultrasounds to monitor the kidneys are recommended once kidney function and growth are stable.
For patient referral or consultations, contact the Department o f Pediatric Urology at Children's Hospital of Pittsburgh of UPMC at 412-692-4100.
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