Prenatal hydronephrosis is the swelling of a kidney in a fetus or infant. The condition is usually found during prenatal ultrasounds. The swelling is typically caused by a buildup of urine in the kidney. Treatment may involve observation, antibiotics, or surgery to correct the blockage.
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What Is Prenatal Hydronephrosis?
Prenatal hydronephrosis is the swelling of a kidney in a fetus or infant. The swelling is typically caused by the buildup of urine inside the renal pelvis, an area of the kidney.
Other names for this condition include antenatal or fetal hydronephrosis, or dilated or enlarged urinary tract.
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 the renal pelvis first then flows down the ureters – two thin tubes that connect each kidney to the bladder. From the bladder, urine leaves the body through a tube called the urethra.
What are the types of prenatal hydronephrosis?
Hydronephrosis can be:
- Bilateral – Affecting both kidneys.
- Unilateral – Affection just one kidney.
In addition, prenatal hydronephrosis is graded on a scale from mild to moderate to severe, based on the amount of swelling shown in the kidney draining system on ultrasound.
How common is prenatal hydronephrosis?
Prenatal hydronephrosis is the most common problem found on prenatal ultrasounds. It is relatively common, affecting about 1 in 100 babies.
What causes prenatal hydronephrosis?
Potential causes of prenatal hydronephrosis are:
- Bladder disorders – Disorders such as posterior urethral valves, neurogenic bladder, or congenital bladder outlet obstruction due to urethral stricture.
- Ectopic ureter – A condition where a child is born with a ureter that does not connect at the bladder but instead drains outside of the bladder.
- Idiopathic – The cause is unknown because, in more than half of babies diagnosed before birth, the condition goes away on its known.
- Megaureter – An abnormality of one or both ureters.
- Neurogenic bladder – When nerves near the bladder do not carry messages properly from the bladder to the brain and from the brain to the bladder muscles.
- Posterior urethral valves (PUV) – A blockage of the urethra – the tube that carries urine from the bladder through the penis – that happens only in boys.
- Ureterocele – A birth defect that affects the kidney, ureters, and bladder, blocking the flow of urine.
- Ureteropelvic junction (UPJ) obstruction – Blockage at the junction of the renal pelvis of the kidney and the ureter (tube that carries urine from the kidney to the bladder).
- Ureterovesical junction (UVJ) obstruction – Blockage at the junction of the bladder and the ureter (tube that carries urine from the kidney to the bladder).
- Vesicoureteral reflux – A backflow of urine into the ureters and sometimes the kidneys from the bladder.
Prenatal hydronephrosis risk factors
Risks of severe prenatal hydronephrosis for the baby include:
- Increased risk of urinary tract infections (UTIs), which can cause pyelonephritis (kidney infections).
Risks of severe prenatal hydronephrosis for the mother include:
- Increased risk of urinary tract infections (UTIs).
- Increased risk of sepsis, a life-threatening condition especially during in pregnancy.
Complications of prenatal hydronephrosis
Complications of severe prenatal hydronephrosis for the baby include:
- Chronic kidney disease, which could require dialysis or kidney transplant.
- Impaired lung development due to low amniotic fluid.
- Kidney stones later in life.
- Permanent kidney damage.
Complications of severe prenatal hydronephrosis for the mother include:
- Perinatal complications, such as premature membrane rupture.
- Premature onset of labor.
What Are the Signs and Symptoms of Prenatal Hydronephrosis?
Most children with hydronephrosis have no symptoms. Prenatal hydronephrosis is often found in fetuses during routine ultrasounds.
However, children with hydronephrosis may be at higher risk for urinary tract infections (UTIs).
Common symptoms of UTI in children may include:
- Back pain.
- Burning with urination.
- Cloudy urine.
- Fever.
- Strong or sudden urge to urinate.
- Vomiting.
Common symptoms of UTI in babies may include:
- Fever
- Irritability
- Poor feeding
If a UTI is suspected, it's best to get a urine sample using a catheter to decrease the chance of contaminating the urine.
When should I see a doctor for my child's symptoms?
Call your child’s provider right away if they have:
- Blood in the urine.
- Fever of 101.5°F no matter what age.
- Pain with urination.
- Persistent irritability or poor feeding in babies.
- Severe pain in the belly, low back, or side.
How Do You Diagnose Prenatal Hydronephrosis?
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. It 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.
Tests to diagnose prenatal hydronephrosis
- 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 the kidney and does not wash out in the urine, blockage is diagnosed.
How Do You Treat Prenatal Hydronephrosis?
Prenatal hydronephrosis is often found in fetuses during routine ultrasounds. Sometimes, it goes away without treatment. Often, mild cases do not adversely affect kidney function and require only monitoring.
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.
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.
Antibiotics
Most cases of vesicoureteral reflux are treated with daily antibiotic therapy. Prenatal hydronephrosis is often treated with antibiotics to prevent kidney infections.
Surgery
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.
Minimally invasive techniques provide significant benefits, including:
- Faster recovery.
- Minimal scars.
- Reduced postoperative pain.
In one such procedure, called laparascopic pyeloplasty, a laparascope (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 through 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 the body heals.
Currently, this operation is being used in older children and adults and eventually will be used to treat toddlers and even infants. The hospital stay for either open or laparoscopic pyeloplasty is usually about one to three days.
The success rate is generally 95% for all open operations, and that rate appears to be similar for laparoscopic operations.
