An encephalocele is a rare birth defect where brain tissue and its surrounding membranes push through an opening in the skull that didn’t close properly during early pregnancy. It belongs to a group of conditions called neural tube defects, which also includes spina bifida and anencephaly. The protruding tissue typically forms a visible sac on the head, and the size can range from small and barely noticeable to larger than the head itself.
How an Encephalocele Forms
During the first weeks of pregnancy, a flat sheet of cells called the neural tube folds and closes to form the brain and spinal cord. This process is usually complete by the fourth week of pregnancy, often before a person even knows they’re pregnant. When part of the skull portion of the neural tube fails to close, a gap is left in the bone. Pressure from the brain’s normal growth can then push tissue outward through that gap, creating a sac covered by skin or a thin membrane.
The sac may contain only the protective membranes that surround the brain (called a meningocele) or it may also contain brain tissue itself. When brain tissue is involved, the condition is more serious and the neurological effects tend to be greater. By about 13 weeks of pregnancy, an ultrasound can distinguish between a sac containing only membranes and one containing brain tissue.
Types Based on Location
Encephaloceles are classified by where they appear on the skull:
- Occipital: At the lower back of the head. This is the most common type, accounting for roughly 70% to 90% of all cases.
- Parietal: Near the top of the head, toward the back.
- Frontoethmoidal (sincipital): Near the forehead, sometimes extending toward the nose or eye sockets. This type can be further broken down into nasofrontal (projecting along the nasal bridge), nasoethmoidal (protruding into the nasal cavity), and nasoorbital (extending along the inner wall of the eye socket).
Location matters for both symptoms and outlook. Occipital encephaloceles frequently occur alongside other brain abnormalities and carry a higher risk of developmental problems. Frontoethmoidal encephaloceles generally have a better prognosis, though they can cause significant facial distortion if not corrected early. Interestingly, frontoethmoidal encephaloceles are far more common in Southeast Asian populations than in Western countries, a geographic pattern researchers have documented but not fully explained.
Causes and Risk Factors
No single cause has been identified. The condition likely results from a combination of genetic changes and environmental exposures during early pregnancy. Encephalocele is associated with more than 30 genetic syndromes, including Meckel syndrome, Walker-Warburg syndrome, and Fraser syndrome. Several chromosomal abnormalities have also been linked to it, including trisomy 13, 18, and 21.
A family history of any neural tube defect, not just encephalocele, raises the risk. Factors in the pregnant person that may increase risk include:
- Low folate levels during early pregnancy
- Poorly controlled diabetes before or during pregnancy
- Certain anti-seizure medications
- Overheating from hot tubs or high fevers in the first trimester
Taking 400 micrograms of folic acid daily before conception and during early pregnancy may lower the risk, though some researchers note the protective effect of folate is better established for spina bifida than for encephalocele specifically.
Signs and Associated Conditions
The most obvious sign is a sac protruding from the skull, which may be visible at birth or detected on prenatal imaging. Beyond the sac itself, the neurological impact depends heavily on which part of the brain is involved and how much tissue has herniated outside the skull.
Occipital and parietal encephaloceles commonly occur alongside a buildup of fluid in the brain (hydrocephalus), which creates additional pressure and can worsen developmental outcomes if untreated. Seizures affect about 17% of children with occipital encephaloceles but are uncommon in the frontoethmoidal type. Occipital encephaloceles may also co-occur with structural brain abnormalities including Chiari malformations and Dandy-Walker malformations, both of which involve the lower parts of the brain.
Children with frontoethmoidal encephaloceles often face problems with facial structure, including widening of the nasal bridge, displacement of the eyes, and impaired binocular vision. Left untreated, these issues worsen as the face grows.
How It’s Diagnosed
Most encephaloceles are detected during routine prenatal ultrasound, typically performed between 11 and 14 weeks of pregnancy. Ultrasound can identify the sac and its general location, and by 13 weeks it can often determine whether brain tissue is present inside the sac.
After birth, MRI is the most valuable imaging tool. It shows soft tissue in detail, revealing exactly what brain structures have herniated, whether there are additional brain abnormalities, and how the sac connects to the inside of the skull. This information is essential for surgical planning. CT scans are sometimes used as well because they provide a clearer picture of the bone defect itself.
Surgical Repair
Surgery is the primary treatment. The goals are to return viable brain tissue to the skull when possible, remove any non-functional tissue that has been damaged by herniation, seal the protective membranes around the brain to prevent infection and fluid leaks, close the gap in the skull, and reconstruct any external bone deformity.
Most surgeons recommend operating within the first few months of life. Early repair makes it technically easier to identify how the sac connects to the brain, and for frontoethmoidal cases, early correction prevents progressive facial distortion during growth. That said, some surgical teams prefer to wait until 5 to 10 months of age to reduce the risks that come with prolonged anesthesia in very young infants, particularly excessive blood loss and difficulty maintaining body temperature.
The bone gap is reconstructed using either a piece of the child’s own skull bone or an artificial material such as titanium mesh. The protective membranes are sealed using tissue from just outside the skull, sometimes reinforced with a biological glue. For frontoethmoidal encephaloceles near the forehead, surgeons typically access the area through an incision behind the hairline, lifting the frontal bone to reach the defect from inside the skull.
Survival and Long-Term Outlook
A CDC study tracking 70 infants born with encephalocele in Atlanta over two decades found that 71% survived to age 1, and 67% survived to age 20. These numbers reflect all types and severities combined.
Long-term outcomes vary enormously depending on the location, the amount of brain tissue involved, and whether other brain abnormalities are present. Children with small frontoethmoidal encephaloceles containing little or no brain tissue often develop normally after surgical repair. Children with large occipital encephaloceles that involve significant brain tissue and concurrent hydrocephalus face a higher risk of intellectual disability, motor difficulties, and vision problems.
Hydrocephalus, when present, typically requires its own ongoing management, sometimes including a shunt to drain excess fluid. Seizures may need long-term treatment as well. Many children benefit from physical therapy, occupational therapy, or developmental support programs in the years following surgery, depending on the extent of neurological involvement.