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Understanding Hydronephrosis
WHAT IS HYDRONEPHROSIS?
Hydronephrosis is a swelling or dilation within
the kidney
or the ureter, which is the tube that connects the kidney
to the bladder and moves the urine the kidneys produce
to the bladder. Hydronephrosis generally results from a
blockage at the top of the ureter near the kidney (known
as the ureteropelvic junction, or UPJ) that traps urine in
the kidney, causing it to build up and stretch the kidney
or ureter. Less commonly, urine backs up
from the bladder and leads to hydronephrosis. Generally
only one kidney is affected. The severity of the condition
depends on the extent of the blockage and the degree the
kidney is stretched, and can range from mild to severe. In
the most severe cases, the UPJ obstruction can lead to
abnormalities in the amount of amniotic fluid, and this in
turn can impair fetal lung development.
HOW COMMON IS HYDRONEPHROSIS AND WHAT CAUSES IT?
Some studies suggest that as many as 2% of all prenatal ultrasound
examinations reveal some degree of hydronephrosis, making it one
of the most commonly detected abnormalities in pregnancy. It is not
clear why the ureter becomes blocked during development. It is more
often seen in boys than girls. Babies with severe UPJ obstructions have
an overall increased chance of having a chromosomal abnormality (like
Trisomy 21, or Down syndrome).
HOW IS HYDRONEPHROSIS DETECTED DURING PREGNANCY?
Ultrasound can detect the fetal kidneys and bladder by 14 or 15 weeks
gestation, though 20 weeks of pregnancy is the ideal time to detect
hydronephrosis on ultrasound, since the fetus is larger and the kidneys
can be visualized in detail. When a UPJ obstruction is identified, the kidneys
are closely examined for other findings more common with UPJ,
such as cysts (known as multicystic, dysplastic kidney) or an abnormal
shape (commonly called a horseshoe kidney).
HOW WILL MY PREGNANCY BE MANAGED NOW THAT HYDRONEPHROSIS HAS BEEN DETECTED?
Through the Carmen and John Thain Center for Prenatal Pediatrics, you
will have an in-depth ultrasound study to confirm the diagnosis, evaluate
the kidneys and bladder closely, and ensure no other abnormalities are
present. The ultrasound will be performed by an obstetrician with expertise
in prenatal ultrasound and high-risk pregnancy, a Maternal-Fetal Medicine (or MFM) specialist. Many times a Pediatric Urologist will also
be present during the exam to review the findings with you and discuss
the possible course of treatment after birth. Amniocentesis to rule out a
chromosomal abnormality in the baby can also be performed if you like.
You will have periodic sonograms to monitor the baby’s kidneys and fluid;
in cases of bilateral UPJ obstruction or when a kidney is missing or cystic
in appearance, ultrasound may be repeated every 2-3 weeks to check
the obstruction and level of amniotic fluid.
In addition to the Pediatric Urologist, you and your family will also meet
with a few other specialists during your pregnancy who will be involved in
caring for the baby after birth. If surgery is likely in the baby after birth,
you may tour the Neonatal Intensive Care Unit (or NICU) and discuss
how your baby will be cared for in the first few days after he or she is
born. You may also meet with a Genetic counselor and a Geneticist to
talk about your family history, review the causes of hydronephrosis, and
understand what to do if and when you become pregnant again. If the
hydronephrosis is minimal and the UPJ obstruction is only present in one
kidney, you do not need to change your prenatal care, and a normal
delivery can be expected. When the hydronephrosis is severe and the
UPJ obstruction is found in both kidneys or one of the kidneys is missing
or has a cystic appearance, your medical team may feel it best for you
to deliver earlier than expected, and will discuss this with you in detail
so you can make the best decision for you and your baby.
HOW WILL THE HYDRONEPHROSIS BE TREATED AFTER BIRTH?
Every newborn with a prenatal diagnosis of hydronephrosis will undergo
a detailed physical exam for signs of any consequences from the UPJ
obstruction. Babies with severe cases of prenatal hydronephrosis will
have an ultrasound of the kidneys and bladder a few days after birth;
those with less serious cases may not need the exam for a few more
days. If that ultrasound is normal, a repeat will be performed a few
weeks later to confirm that result. Half of the babies with prenatal
diagnosis of a UPJ obstruction and hydronephrosis will have a normal
result on their newborn scan. Almost all babies with prenatal diagnosis
of hydronephrosis may be given antibiotics to lower the chances for a
urinary-tract infection, a common problem linked to hydronephrosis.
If a UPJ obstruction is seen on newborn ultrasound, treatment is
determined by the severity of the obstruction. In cases where a mild or
moderate obstruction is noted and the kidney has more than 35% normal
function, your medical team may decide to just monitor the kidneys and
repeat the ultrasound in a few months. That repeat scan will determine
any changes in the kidney’s ability to function normally. In severe cases,
when the kidney shows 35% or less function, surgery known as pyeloplasty
may be necessary to remove the obstruction and reconstruct the
urinary tract. Surgery is generally performed after the baby has been
fully evaluated and stable; emergency surgery is not necessary. The success
rate for surgery is 90-95%.
If the prenatal ultrasounds show cysts in the kidney, an ultrasound of
kidney and a special x-ray called a voiding cystourethrogram (VCUG) will
be done to fully determine how the cystic kidney is affected and make
sure the other kidney is normal.
WHAT IS THE LONG-TERM OUTLOOK FOR BABIES WITH HYDRONEPHROSIS?
Many cases of hydronephrosis will resolve on their own before the
baby’s birth. Long-term follow-up studies suggest that most cases
of hydronephrosis at birth will resolve over time, with the kidneys
working normally. For those infants whose newborn testing shows a
persistence of the condition, the long-term outlook depends on whether
the obstruction is present in one or both kidneys and whether one or
both kidneys is cystic in appearance. In the most severe cases, when
hydronephrosis due to UPJ obstruction is seen in both kidneys, or when
one UPJ obstruction is present but the opposite kidney is missing or is
cystic in appearance, the prognosis may be more severe, eventually
requiring kidney transplantation for normal kidney function.
WHAT ARE THE CHANCES I COULD HAVE ANOTHER BABY WITH HYDRONEPHROSIS?
Minimal hydronephrosis is not genetic and is not believed to run in
families. However, given that hydronephrosis is so commonly detected
in pregnancy, it may be coincidentally detected in future pregnancies.
If UPJ obstruction is determined to be the cause of the hydronephrosis,
the chances for future children with the same obstruction are believed
to be as high as 50%. Certain genetic conditions can cause the kidneys to
have cysts, and these generally carry a 25% for future children to have
the same condition. Regardless of the cause, you should have a good
prenatal ultrasound examination in the second trimester with all future
pregnancies to check the developing kidneys and bladder.
WHAT CAN I EXPECT FROM THE SPECIALISTS AT MORGAN STANLEY CHILDREN'S HOSPITAL?
The well-being of you and your baby are extremely important to everyone
involved in your care. NewYork-Presbyterian Morgan Stanley Children’s
Hospital/Columbia University Medical Center has consistently been
ranked one of the best pediatric hospitals in the country: our pediatric
urologists have extensive experience in caring for hydronephrosis, and
our MFM team is among the largest and most experienced anywhere.
Our NICU is one of the most advanced in the United States, and has been
cited several times for its excellence and dedication to patient care.
The well-being of you and your baby are extremely important to everyone
involved in your care. Together we are all dedicated to giving you the
best pregnancy and healthiest outlook for your child.
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