Common CNS Anomalies – What Causes Them and How To Avoid Them

CNS or Central Nervous System Anomalies is the collective term used to define the number of birth defects that arise in utero or while the fetus is developing during pregnancies. CNS anomalies are defects in the development of the spinal cord and brain. Hence CNS abnormalities are usually associated with mortality and morbidity.

Common CNS Anomalies


Anencephaly is a neural tube defect wherein the head of the neural tube, which will eventually form the skull and brain, does not develop properly. By the 4th week of conception, the head of the neural tube starts to close, but with patients with Anencephaly, it doesn’t close all the way. As a result, the fetus’ skull and brain don’t develop fully. Babies with Anencephaly are usually born missing the forebrain and the cerebrum. The skull also doesn’t fully close, so what’s left of the baby’s brain is usually exposed, without the cover of bone and skin.

Anencephaly is more common than you think, with around 1 in every 4,600 births in the US. It is also one of the fatal birth defects, with most babies with Anencephaly dying right after birth. Those that survive usually die within a few hours or days.


Iniencephaly is another neural tube defect that can occur if the neural tube does not close properly. In the case of Iniencephaly, the spine is so deformed that it results in the retroflexion of the infant’s head. The head is sometimes so bent backward that several babies are born without necks, and the face is directly connected to the chest, with the baby’s scalp attached to their back, forcing them to face upwards. A baby can be born with both Iniencephaly and Anencephaly.

Similar to Anencephaly, there is no course of treatment for Iniencephaly as most infants born with the condition die a few hours after birth.

Spina Bifida

Spina Bifida is a neural tube defect that, unlike Anencephaly and Iniencephaly, can vary in its severity. Mild cases of Spina Bifida are called Occult, or Hidden Spina Bifida. This occurs when the neural tube doesn’t close fully and creates a minor separation or gap along the baby’s vertebrae. The separation is small and almost unnoticeable unless the infant undergoes imaging tests. Because the separation is minimal, babies with Occult Spina Bifida can grow up to live full and healthy lives.

The severe type of Spina Bifida is called Myelomeningocele, or Open Spina Bifida. This happens when the gaps and separation between the bones of the spinal canal are so large that the nerves and membranes spill out, forming sacks along the baby’s back made out of exposed tissues and nerves. The tissues and nerves may get infected, which can endanger the baby’s life.

Surgery immediately after birth can give babies with Myelomeningocele a chance at life. However, depending on the severity of the exposed tissues and nerves, even with surgery, babies with Myelomeningocele will require therapy and treatment throughout their lives for complications such as paralysis and diminished bladder/bowel functions.


Holoprosencephaly is the failure of the brain to separate into two hemispheres, resulting in deformities in the head and face. There are 4 types of Holoprosencephaly: Alobar, Semi-lobar, lobar, and MIHV or middle interhemispheric variant. MIHV is the mildest form of Holoprosencephaly and occurs when the brain is divided but not fully. Babies with MIHV are born with eyes too close together, while babies born with Alobar, the most severe form of Holoprosencephaly, may end up with only one central eye, a condition known as Cyclopia.

Aside from deformities in eye placement, babies with Holoprosencephaly may also show signs of neural tube defects, Hydrocephalus, intellectual disability, pituitary gland dysfunction, and experience frequent seizures. Babies who grow up with Holoprosencephaly are usually stunted, experience breathing problems, have irregular heartbeats and experience abnormal body temperatures.

Fetuses with Alobar Holoprosencephaly are usually stillborn, while some die within a few days after birth. However, around 50% of babies born with mild Holoprosencephaly are alive by the time they celebrate their first birthday. Lifelong treatment and management of symptoms are required for people with Holoprosencephaly.

Chiari Malformations

The foramen magnum is an opening at the base of a person’s skull where the spinal cord passes through. On the other side of the foramen magnum, you can find parts of the brain stem, as well as the cerebellum, the part of the brain in charge of balance control.

When abnormalities occur in the development of a person’s brain and skull, sometimes the skull is too small to house parts of the brain effectively, and the cerebellum ends up pushing down past the foramen magnum and into the spinal cord. When this happens, it’s called a Chiari Malformation.

Because the cerebellum is pushing against the spinal cord, it can hamper the flow of cerebrospinal fluid, depriving the brain and spinal cord of the nutrients and protection they need. Because these malformations also affect the cerebellum, it also causes balance and hearing problems in the affected person.

Unlike other anomalies mentioned in this article, Chiari Malformations are not purely congenital. A person born normally can develop Chiari Malformations later on in life resulting from injuries or diseases where there is excessive draining of the person’s spinal fluid.

This does not mean that Chiari Malformations are mild and should be shrugged off. In severe cases of Chiari Malformations, babies are born with an opening at the back of the head, causing the cerebellum and parts of the brain stem to be completely exposed to the elements.

Dandy-Walker Syndrome/Malformation

Dandy-Walker Syndrome or Malformation is characterized by a malformation in the cerebellum and the areas surrounding it. The cerebellum is surrounded by the 4th ventricle, which is responsible for the safe passage of fluid to and from the upper and lower areas of the brain. The congenital anomaly often presents with an enlarged 4th ventricle, which then blocks spinal fluid resulting in the excess fluid around the brain or Hydrocephalus. Trapped excess fluid creates increased pressure in the brain, leading to neurological deficiencies.

Common signs and symptoms of DWM included learning disabilities and developmental delays. In severe cases where Hydrocephalus isn’t immediately treated, it can lead to mental retardation. Dandy-Walker Syndrome appears once in every 25,000 to 35,000 live births and is more likely to affect females compared to males.


Hydrocephalus means “water in the brain.” This happens when there’s an excess buildup of water in and around the areas of the brain, which causes swelling. Normally, cerebrospinal fluid or CSF flows freely through the brain and spinal column, delivering nutrients and acting as a cushion and protective barrier to these areas. Hydrocephalus may occur if there’s an excess production of CSF in the brain, a blockage that prevents the fluid from flowing freely, or if something is preventing it from being absorbed into the blood.

In many cases, Hydrocephalus is not considered a disease but a sign of something more serious. Hydrocephaly might be a telltale sign of an injury or infection in the brain, such as encephalitis or meningitis. Hydrocephaly in babies is a sign of possible genetic or congenital anomalies like Myelomeningocele or DWM.

What Causes Central Nervous System Anomalies?

The appearance of an anomaly occurs due to several factors. There is no single culprit, and in some cases, malformations occur due to a mixture of different reasons.


Genetic makeup plays a big role when it comes to fetal development. In many cases where the neural tube doesn’t develop properly, a mutation in the genes is usually the culprit. After the egg is fertilized and the embryo starts to develop, a mutation in the genes can occur, and in most cases, only one gene mutation is required to cause a malformation. However, not all gene mutations result in malformation. Some mutations are dormant and don’t show up. In cases like these, babies grow up completely normal. There is a chance that the mutated gene will affect their future offspring.

Environmental Factors

The environment also plays a huge role when it comes to fetal development. As stated earlier, not all gene mutations cause malformations. Some mutations only make people sensitive and at risk for central nervous system malformations, and environmental factors may end up triggering or exacerbating it.

Pregnant women are at risk of giving birth to babies with congenital defects if they work in environments where they handle dangerous chemicals or are exposed to radiation regularly. Any agent that, when exposed, can cause abnormalities or malformations in fetuses is called a Teratogen. Again, simple environmental exposure to teratogens doesn’t guarantee malformations due to genetics. For example, a mother working in a factory is exposed to herbicides daily. However, if the fetus’ genetic makeup is resistant to herbicides, the possibility of malformations is decreased.


Poor lifestyle choices increase the risk for CNS anomalies exponentially. A pregnant woman who smokes, consumes alcohol, and takes harmful substances is more likely to give birth to a child with congenital defects. The same is true for women who are malnourished and don’t make an effort to eat healthily and supplement their diet with vitamins and minerals.

Injury to the fetus can also lead to malformations as it disrupts the normal development of the neural tube and other parts of the body. Women who suffer domestic abuse often receive more abuse while they are pregnant, and this can not only harm the mother but the developing baby as well.

How To Minimize The Risk of CNS Anomalies

Women should make an effort to minimize their risk for Central Nervous System anomalies. These malformations have proven to be devastating to families, not only because most result in stillbirths or infant death, but children that do survive require a lifetime of treatment and care.

Don’t smoke, consume alcohol, or take drugs

Obvious as it may be, there is no surer way to decrease the chances for CNS anomalies other than staying away from harmful substances. Drugs, alcohol, and smoking – any intake of harmful substances for that matter will always result in pregnancy problems, even if they don’t result in CNS anomalies. Even if born free from congenital defects, babies born to mothers who use harmful substances while pregnant experience developmental delays, low birth weight, and are susceptible to health problems in the future.

Plan for your pregnancy before you get pregnant

Obstetricians keep campaigning for pre-pregnancy planning, and there is a good reason for that. As stated in the previous paragraph, women are advised against the consumption of harmful substances. And while most women do stop smoking and drinking alcohol as soon as they find out they’re pregnant, it is important to note that most women find out they are pregnant 4-6 after conception.

The neural tube has already developed by this time and is on its way to closing. So by 4 to 6 weeks of pregnancy, the damage is already done. If you are a heavy drinker or smoker and you stopped as soon as you find out you’re pregnant, it may already be too late.

Take the recommended daily dose of folic acid

Another reason why it’s important to plan for your pregnancy before you conceive is that your body needs more folate during the first month of pregnancy. Doctors recommend that pregnant women take 400 μg of folic acid per day. Folic acid reduces the risk of neural tube defects exponentially, so it’s advisable to start taking folic acid even before conception and continue taking it until the end of the first trimester.

Again, the problem is that women usually find out about their pregnancy around the 4-6 week mark and start taking supplements around this time, missing the golden window of opportunity to fully protect their babies from neural tube defects.

A change in environment

If your workplace or your residence subjects you to harmful teratogens daily, you may want to consider a change of employment or residence. Teratogens not only increase the risk of congenital defects but can also increase the chance of miscarriage and stillbirth.

Seek medical help for illnesses

The majority of people do not seek medical treatment when they fall ill. Most of the time, they self-medicate and rest until they get well. When you are pregnant, it’s better to seek medical help if you are sick. Having a high fever for several days can affect your fetus, and a simple infection like UTI is manageable for adults, but any infection, once it crosses over to the fetus, can be potentially life-threatening.

While pregnant, it’s also important to steer clear of potential hazards. Stick to cooked food and avoid contact with animal feces.