An Overview of Skull Birth Defects: Anencephaly, Craniosynostosis, and Encephalocele

Skull birth defects are conditions that are present at birth. These birth defects were created when a baby was still developing in the womb. This overview will discuss three of the most common skull birth defects in babies: anencephaly, craniosynostosis, and encephalocele.

What Is Anencephaly?

Anencephaly is a type of neural tube defect (NTD) in which a baby is born without parts of the brain and skull. Approximately 1 in every 4,600 babies in the United States is born with anencephaly.

The neural tube is formed very early in pregnancy. As it develops and closes, it helps form the baby’s brain, skull, spinal cord, and backbone.

If the upper part of the neural tube does not close all the way, anencephaly occurs. The baby is often born without the forebrain (the front part of the brain) and the cerebrum (the part of the brain responsible for thinking and coordination). Often, the rest of the brain is not covered by bone or skin.

Anencephaly happens during the third and fourth weeks of pregnancy. The rest of the baby's body continues to grow and form throughout the pregnancy.

The exact cause of anencephaly is not known, but it is believed to be caused by a combination of environmental factors, genetics, and nutrition during pregnancy. In most cases, there is no family history of it or other neural tube defects. In some instances, a familial pattern is suspected.

Some risk factors for anencephaly include:

• Lack of enough folic acid (at least 400 micrograms of folic acid is needed each day before and during pregnancy)
• Uncontrolled diabetes in pregnancy
• High body temperature (from a fever or using a hot tub or sauna during early pregnancy)
• Medications such as Dilantin (phenytoin), Tegretol (carbamazepine), and Depakote (valproic acid)
• Obesity before pregnancy
• Opioid use
• Infection
• Being around hazardous chemicals and materials
• Hispanic ethnicity of the pregnant person

Anencephaly is more common in girls than boys.

Anencephaly is associated with these conditions:

• Folding of the ears
• Cleft palate (a split in the roof of the mouth)
• Congenital heart defects

Diagnosis

Anencephaly is often diagnosed before birth. If it is missed prenatally, it is immediately apparent through appearance when the baby is born.

Anencephaly may be diagnosed prenatally using tests and diagnostic tools such as:

Quad marker screen:

• It is a blood test.
• It checks for neural tube defects and genetic disorders.
• One of the tests is to look for higher levels of the protein alpha-fetoprotein (AFP), which is higher in the pregnant parent’s blood if the baby has anencephaly.

Ultrasound:

• Uses sound waves to produce pictures of the unborn baby
• Used to look at the baby’s skull, brain, and spine

Fetal magnetic resonance imaging (MRI):

• Produces images of tissues and bones using high-powered magnets
• Looks at the baby's brain and spine in greater detail

Amniocentesis:

• A small amount of fluid is removed using a thin needle inserted into the amniotic sac (the bag of fluid around the fetus).
• The fluid is checked for high levels of AFP and an enzyme called acetylcholinesterase, either of which may indicate the baby has a neural tube defect.

Treatment

There is no treatment for anencephaly. Most pregnancies with anencephaly end in miscarriage or stillbirth. Babies who are born with anencephaly will almost always die within a few hours or a few days.

Treatment is supportive and involves helping parents and loved ones say goodbye and grieve their baby.

What Is Craniosynostosis?

A typical baby’s skull bones have spaces between them called sutures. They are filled with flexible material. These sutures stay open until around 2 years of age, to allow room for the baby's brain to grow. At around age 2, the sutures become bone and begin to "close" by joining together.

Craniosynostosis occurs when one or more of the sutures closes too early. This premature closure can limit or slow the growth of the baby’s brain. Approximately 1 in every 2,500 babies is born with craniosynostosis in the United States.

Craniosynostosis can affect one, some, or all of the sutures. When a suture closes too early, the baby's head will stop growing in that area, but the rest of the skull will continue to grow. This may cause:

• An abnormally shaped skull
• Lack of room for the brain to grow to its proper size
• A buildup of pressure in the skull

Depending on how many sutures are affected and how much room there is, the brain may still grow to its usual size.

The types of craniosynostosis are determined by where the sutures close.

Sagittal craniosynostosis:

• Affects the suture on the top of the head
• Often causes a long, narrow head (scaphocephaly)

Coronal craniosynostosis:

• Affects one of the coronal sutures (run from both ears to the top of the head)
• May cause a flat forehead and a broad head

Lambdoid craniosynostosis:

• Affects the suture along the back of the head
• May cause a flat back of the head (plagiocephaly)

Metopic craniosynostosis:

• Affects the suture that runs from the top of the nose to the top of the forehead
• May cause a triangular head, with the narrow ridge at the midline of the forehead

If left untreated, craniosynostosis can lead to:

• Developmental delays
• Seizures
• Vision or eye movement disorders
• Breathing difficulties, especially if other bony abnormalities of the face are present
• Persistent head or facial deformities

The exact cause of craniosynostosis isn't known but may be the result of a combination of genes and other factors such as:

• Environmental contacts while pregnant
• Nutrition
• Thyroid disease during pregnancy
• Use of fertility medications such as clomiphene citrate (Clomid)
• Premature birth

Diagnosis

Craniosynostosis is usually diagnosed soon after birth, but it may be diagnosed later in life.

During a physical exam, the healthcare professional will look for symptoms such as:

• An abnormally shaped skull
• No fontanelle ("soft spot”) on the baby’s skull
• A raised firm ridge of bone on the baby's head
• Slow growth or no growth in the size of the baby’s head over time

An X-ray or computed tomography (CT) scan may be ordered to help confirm a suspected diagnosis of craniosynostosis.

Treatment

Treatment depends on the severity of the condition. Some forms of craniosynostosis are mild and require little intervention, while others are more severe and may need more intensive treatments.

Treatments for craniosynostosis may include:

• Helmet therapy: A special medical helmet may be used to gently reshape the skull over time.
• Surgery: This may be necessary to reshape the skull, relieve pressure in the skull, and allow the baby’s brain room to grow and develop properly.
• Supportive therapies: Physical therapy, occupational therapy, and speech therapy may be necessary for some children with craniosynostosis.

What Is Encephalocele?

Encephalocele is a birth defect that happens when the neural tube does not close completely during pregnancy. Encephalocele occurs in approximately 1 in every 10,500 babies born in the United States.

With encephalocele, part of the baby's brain and the membranes that cover it come through a hole in the skull. The protruding brain is covered in either skin or a thin membrane, creating a "sac."

The opening can be anywhere along the center of the skull from the nose to the back of the neck, but is usually at the back of the head, at the top of the head, or between the forehead and the nose.

Genetics may play a role in causing an encephalocele. Encephalocele occurs more frequently in families that have a history of neural tube defects (spina bifida and anencephaly).

More research is needed into the causes of encephalocele. As with other neural tube defects, 400 micrograms of folic acid taken daily before and during pregnancy is believed to help prevent encephalocele.

Symptoms and conditions that may occur with encephalocele include:

• Hydrocephalus (too much cerebrospinal fluid in parts of the brain)
• Microcephaly (a very small head)
• Seizures
• Vision problems
• Breathing problems (if there is a large encephalocele near the nose)
• Problems with swallowing
• Pain around the encephalocele
• Delayed growth and development
• Spasticity (high muscle tone) or other movement disorders
• Pituitary problems
• Differences with the bones in the skull and face
• Loss of strength in the arms and legs
• Uncoordinated use of muscles needed for movement (such as walking and reaching)
• Developmental delay
• Intellectual disability

Diagnosis

Encephalocele is usually apparent at birth, but small encephaloceles (usually in the nose, sinuses, or forehead) may not be noticed right away.

Sometimes encephalocele is observed during a prenatal ultrasound. When this happens, fetal magnetic resonance imaging (MRI) may be ordered.

Treatment

Treatment for encephalocele usually involves surgery (or several surgeries) to place the brain tissue and membranes back into the skull and repair the opening. If needed, a shunt may be put in to drain cerebrospinal fluid (CSF) from around the brain.

Once the encephalocele is treated, the child may need further or ongoing treatment for any conditions or symptoms caused by the encephalocele that remain.

Summary

Anencephaly, craniosynostosis, and encephalocele are three types of skull birth defects. They vary in whether they can be detected before birth, at birth, or later. Anencephaly cannot be treated and is fatal. Encephalocele usually requires surgery to repair. Craniosynostosis may require no intervention or need therapy or surgery.