Cranium Bifidum

What cranium bifidum is

In the first 4 weeks of pregnancy, a flat sheet of cells rolls up to form the neural tube, which becomes the brain and spinal cord. The skull and spine then form around it. If the tube or the overlying bones do not close properly at the head end, a defect in the skull results. Cranium bifidum is to the skull what spina bifida is to the spine.

Types of cranium bifidum

Encephaloceles are most common at the back of the head (occipital) in North America and Europe, and at the front (between the forehead and nose) in parts of Southeast Asia.

Causes and risk factors

• Neural tube closure problems in early pregnancy, the same process behind spina bifida and anencephaly
• Low folate: folate deficiency before and in early pregnancy increases the risk of all neural tube defects
• Genetic factors: enlarged parietal foramina are often inherited in an autosomal dominant pattern (genes such as ALX4 and MSX2). Some encephaloceles occur as part of syndromes such as Meckel-Gruber syndrome
• Maternal diabetes and obesity, some anti-seizure medicines (such as valproate), and high temperatures in early pregnancy
• A previous pregnancy affected by a neural tube defect

Symptoms

Cranium bifidum occultum

Small hidden defects usually cause no symptoms and may be found by chance. Larger openings can leave the brain less protected in the area.

Meningocele and encephalocele

• a visible sac on the head, from small to larger than the baby's head
• hydrocephalus, a build-up of fluid in the brain, causing a large or rapidly growing head
• developmental delay and learning disability, depending on how much brain is involved
• seizures
• vision problems
• weakness or stiffness of the limbs
• feeding difficulties
• small head size (microcephaly)

Babies whose sac contains only meninges and fluid usually do much better than those whose sac contains significant brain tissue.

Diagnosis

• Prenatal screening: many open defects are seen on the mid-pregnancy anatomy ultrasound; a raised alpha-fetoprotein (AFP) in the mother's blood may be a clue. Fetal MRI gives more detail
• After birth: examination of the head and nervous system
• CT scan: shows the bone defect
• MRI: shows whether brain tissue is in the sac and checks for other brain abnormalities and hydrocephalus
• Genetic testing if a syndrome is suspected

Treatment

• Small hidden defects: usually observation only. Some children are advised to avoid high-impact contact sports or wear head protection if the defect is large, and very large parietal foramina may be repaired
• Meningocele and encephalocele: surgery by a pediatric neurosurgeon, usually in the first days to months of life. The sac is opened, non-functioning tissue is removed, functional brain tissue is placed back inside the skull where possible, and the coverings and skin are closed. Skull reconstruction may follow
• Hydrocephalus: a shunt or other procedure to drain fluid
• Ongoing care: anti-seizure medicines, physical, occupational and speech therapy, eye care and developmental support

Outlook

Outlook ranges widely. Cranium bifidum occultum often has no effect on health. For encephalocele, the amount of brain tissue in the sac, the presence of hydrocephalus and other malformations determine development. Many children with small meningoceles and no other brain differences develop normally after surgery.

Prevention

Everyone who could become pregnant is advised to take 400 micrograms of folic acid every day, starting at least one month before conception. People who have had a pregnancy affected by a neural tube defect usually need a higher dose of 4 mg (4,000 micrograms) daily, on prescription, from before conception. Controlling diabetes and reviewing medicines before pregnancy also lower the risk.

Frequently asked questions

What is cranium bifidum?

It is a birth defect in which the skull bones do not close fully, leaving a gap. In the hidden form, only bone is affected and it is often harmless. When the brain's coverings or brain tissue push through the gap, it forms a meningocele or encephalocele, which needs surgery.

Is cranium bifidum occultum serious?

Usually not. It is a small gap in the skull bone with normal skin and brain, often found by chance. Most children have no symptoms. Larger openings may need protection or repair, and doctors check for any associated brain differences.

How is cranium bifidum different from spina bifida?

Both are neural tube defects. Cranium bifidum affects the skull, while spina bifida affects the spine. Both result from incomplete closure of the neural tube in early pregnancy, and folic acid lowers the risk of both.

Can cranium bifidum be prevented?

The risk of neural tube defects, including encephalocele, is reduced by taking 400 micrograms of folic acid daily before conception and in early pregnancy. Inherited forms such as enlarged parietal foramina cannot be prevented, but genetic counseling can explain the chance of recurrence.