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Congenital brain defects are abnormalities in the brain that are present at birth. There are many different types of these defects. They can vary greatly from mild to severe conditions.
The brain begins to form in the first month after conception, and will continue to form and develop throughout pregnancy. Development of the brain begins from a small, special plate of cells on the surface of the embryo. These cells grow and form the different regions of the brain.
When this process is disturbed or interrupted, it can cause structural defects in the brain and skull. Normal brain function can be impaired even if only the skull’s growth is upset.
Keep reading to learn more about congenital brain defects.
Symptoms of congenital brain defects vary. Each defect has a distinct set of symptoms and impairments.
Some of these symptoms may not be apparent until after birth when your child exhibits developmental or growth delays. Some congenital brain defects don’t have symptoms until adulthood. Some never have symptoms at all.
Children born with congenital brain defects also may have:
Several types of congenital brain defects are caused by neural tube defects.
Early in fetal development, a flat strip of tissue along the back of the fetus rolls up to form the neural tube. This tube runs along most of the length of the embryo.
The neural tube typically closes between the third and fourth week after conception. It develops into the spinal cord with the brain at the top. If the tube doesn’t close properly, the tissue within the tube can’t develop properly. Neural tube defects that can occur as a result include:
Anencephaly: The head end of the neural tube fails to close, and a major portion of the skull and brain is missing. The missing portion of the skull means that brain tissue is exposed.
Encephalocele: A portion of the brain bulges through an opening in the skull. The bulge is often located along the front-to-back midline at the back of the skull.
Arnold-Chiari or Chiari II: Part of the cerebellum, a region of the brain that affects motor control, is shifted downward into the upper spinal column. This causes the brain or spinal cord to become compressed.
Other types of congenital brain defects develop within the structure of the brain:
Hydrocephalus: Also called fluid on the brain, this is an excessive buildup of cerebrospinal fluid (CSF) caused by impaired circulation of the CSF. When there is excess fluid, it can put too much pressure on the brain.
Dandy-Walker syndrome: This involves the absence or defective growth of the central section of the cerebellum.
Holoprosencephaly: The brain doesn’t divide into two halves, or hemispheres.
Megalencephaly: This condition causes a person’s brain to be abnormally large or heavy.
Microcephaly: This occurs when the brain doesn’t develop to full size. The Zika virus can cause microcephaly.
Most congenital brain defects can’t be attributed to a specific cause. A variety of genetic and environmental factors have been linked to the development of congenital brain defects. These factors may be related to:
Some brain defects are symptoms of trisomy. Trisomy occurs when a third chromosome is present where typically there are only two chromosomes.
Dandy-Walker syndrome and Chiari II defects are associated with trisomy of chromosome 9. Trisomy of chromosome 13 can cause holoprosencephaly and microcephaly. Symptoms of trisomy of chromosomes 13 and 18 can include neural tube defects.
Some risk factors such as genetics are unavoidable. If you’re pregnant or planning to become pregnant, there are some things you can do to reduce the risk for congenital brain defects in your baby:
Infections such as rubella, herpes simplex, and varicella zoster can also increase your baby’s risk for congenital brain defects. While you can’t always avoid infections, there are things you can do to reduce your risk for infection:
Any type of trauma to the unborn child, such as falling on your stomach while pregnant, also can affect brain development.
Your doctor may be able to identify a congenital brain defect by detailed ultrasound. If further investigation is needed, an MRI scan might be used to see details of the brain and spine of the fetus.
It may be possible to identify a congenital brain defect as part of a prenatal screening. This can be done by using chorionic villus sampling (CVS) when you’re between 10 to 12 weeks pregnant. CVS is used to identify various genetic conditions. Not all congenital brain defects are genetic, so CVS will not always identify a congenital brain defect. Talk to your doctor to learn more about CVS.
In some cases, accurate diagnosis may not be possible until after birth when signs such as intellectual disabilities, delayed behavior, or seizures may be more noticeable.
Treatment varies depending on the type and severity of the condition. Many treatments will focus on treating the symptoms. For example, anticonvulsant medications can help reduce episodes of seizures.
Some conditions can be treated with surgery. Decompression surgery can create more space for brain and cerebrospinal fluid where needed. Surgery to correct defective skulls can give the brain space to grow normally. Shunts can be inserted to drain the cerebrospinal fluid that builds up with hydrocephalus.
The effects of a congenital brain defect vary greatly. The type and severity of the condition, the presence of other physical or mental impairments, and environmental factors can contribute to the outlook.
Many congenital brain defects cause minor neurological impairment. People with these types of congenital brain defects can grow to function independently. Other defects are so severe that they are fatal before or shortly after birth. Some cause significant disabilities. Others partially disable people, limiting their mental functioning to a level that is below normal capacity.
Research and tracking of the incidence of birth defects has helped medical experts identify specific ways to reduce congenital brain defects.
The Centers for Disease Control and Prevention recommends that women who are pregnant or considering pregnancy do the following:
Written by: Anna Giorgi
Medically reviewed on: Dec 06, 2016: Karen Gill, MD
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