Congenital Bladder Neck Obstruction - Causes, Diagnosis, and Treatment

Introduction:

Congenital bladder neck obstruction is a rare birth defect in which the fetus has a blockage in the urethra (carries urine out of the bladder and empties into the amniotic sac). It is also called lower urinary tract obstruction or bladder outlet obstruction. A congenital bladder neck obstruction can cause serious complications such as bladder damage, kidney damage, kidney failure, lack of amniotic fluid, underdeveloped lungs, and difficulty breathing. Congenital bladder neck obstruction is more common in males.

What Are the Causes?

• The cause is unknown.

• Genetics may be one of the causes.

What Are the Types of Congenital Bladder Neck Obstruction?

• Posterior Urethral Valve Obstruction: In this condition, a small tissue blocks the urethra resulting in urinary obstruction.

• Urethral Atresia: In this condition, the urethra is completely missing or closed, resulting in no outlet from the bladder into the sac.

• Urethral Stenosis: In this condition, the urethra is so narrow- that the urine cannot flow out in large amounts.

How Does Lower Urinary Obstruction Affect the Baby?

• Bladder Damage: Since there is no urine outlet, the fetal urine overfills the bladder. This causes the bladder to be enlarged and thus damages the thin-walled structure.

• Kidney Damage and Kidney Failure: As the urine gets retained for a longer time, it results in overpressure of the fetal kidneys. This leads to progressive and permanent damage, thereby increasing the risk of kidney failure.

• A Lack of Amniotic Fluid: Major content of amniotic fluid is fetal urine. Thus, when the urine is blocked, and there is no outlet into the sac resulting in oligohydramnios (too low amniotic fluid) or anhydramnios (no fluid).

• Underdeveloped Lungs and Breathing Difficulties: Amniotic fluid is essential for fetal breathing and lung development inside the womb. Without adequate fluid, the baby's lungs are too small to support their oxygen needs at birth.

• Deformities of the Face and Extremities: Lack of amniotic fluid results in Potter sequence- deformities in the physical appearance.

How to Diagnose Congenital Bladder Neck Obstruction?

• Congenital bladder neck obstruction is diagnosed in the later stage of the first trimester or earlier in the second trimester through routine ultrasound.

• On imaging, the fetal bladder appears enlarged, the kidneys are swollen, and low amniotic fluid.

• The enlarged bladder and dilated urethra may resemble a keyhole in ultrasound, which is known as a keyhole sign of lower urinary tract obstruction.

What Are the Tests Done to Confirm the Diagnosis?

• Anatomy Ultrasound: It is used to confirm the diagnosis and evaluate the obstruction. It is also used to look for other abnormalities.

• Fetal Magnetic Resonance Imaging: It is used to get detailed information about the severity of the baby's condition.

• Fetal Echocardiogram: It is used to evaluate the fetal heart.

• Amniocentesis and Chromosomal Analysis: It is used to detect genetic abnormalities.

• Fetal Bladder Tap: Vesicocentesis is done to obtain the urine sample and helps to assess kidney function.

What Is the Treatment Plan?

Treatment depends on the severity of the condition and kidney functioning. Mild cases will have little effect on the fetus, and thus close observation is needed. Moderate cases require surgery after birth. And in severe cases, fetal intervention is needed.

What Are the Interventions Done During Pregnancy?

• Repeating the Fetal Bladder Drain: Vesicocentesis is done to obtain the urine sample and helps to assess the kidney function.

• Fetal Shunt Placement:

  • A shunt or draining tube is placed inside the fetal bladder such that one end is within the bladder and the other end is left in the fetal stomach.
  • This hollow tube allows the fetal urine to drain into the amniotic sac.
  • The goal of this procedure is to maintain a normal amniotic fluid level in the sac for proper lung development and also to improve the chance of living after birth.
  • The placement of the shunt also will reduce the pressure inside the bladder and kidneys. However, it will not help to prevent the fetus from further kidney damage.

• Procedure:

  • Fetal shunt placement is done as an inpatient procedure.
  • Intravenous sedation is given to the mother, which sedates the fetus too.
  • Also, antibiotics and local anesthesia are given to the mother during the procedure.
  • An injection is given to the fetus to temporarily paralyze them during the procedure and for pain management.
  • This is a minimally invasive procedure. With the help of ultrasound guidance, a needle is inserted into the mother's abdomen and uterus, and then a shunt is placed in the fetal bladder.
  • Additional fluid is added to the amniotic sac during the procedure.
  • The shunt will be in place till birth.
  • Mother and baby will be monitored periodically till birth.

How to Identify the Baby Requires Intervention?

However, it is difficult to determine with the help of prenatal evaluation; some standard tests help to carry out the procedure. The standard tests to identify fetal intervention include:

• The chemistry of fetal urine.

• Amniotic fluid levels.

• Chromosome analysis.

How Should the Delivery Be Performed?

• Babies with lower urinary tract obstruction should be delivered at a hospital equipped with a neonatal intensive care unit and breathing support for the underdeveloped lungs of the newborn.

• Delivery and postnatal care should be monitored as planned and coordinated with a multidisciplinary team.

• However, lower urinary tract obstruction does not impact the option for vaginal or Cesarean section delivery.

How Should Postnatal Care Be?

• After birth, urologists and pediatric nephrologists will conduct additional tests to analyze the kidney and bladder function of the fetus.

• Some babies need to stay in the intensive care unit for a week or months, depending on the severity of the kidney damage and lung function.

• Some babies require surgery to drain the urine through vesicostomy (a procedure done to drain the urine). This is not a permanent procedure.

• Sometimes additional therapy and renal replacement therapy, which includes dialysis or kidney transplant, is required if there is kidney damage.

Conclusion:

Treatment for congenital bladder neck obstruction varies from watchful waiting to medical therapy to surgery, depending on the severity of the symptoms. Sometimes, additional therapy may be required in cases of kidney damage. Surgical intervention is carried out by carefully weighing the potential risks and benefits before proceeding.