An encephalocele is a rare birth defect in which brain tissue and its surrounding membranes push through an opening in the skull that didn’t close properly during fetal development. It occurs in roughly 1 to 4 out of every 10,000 births worldwide, with rates slightly higher in low-income countries. The result is a sac-like protrusion, sometimes visible on the outside of the head, that contains brain tissue, cerebrospinal fluid, or both.
How an Encephalocele Forms
During the first few weeks of pregnancy, a structure called the neural tube forms and closes to become the brain and spinal cord. When part of the neural tube fails to close completely near the skull, a gap remains in the bone. Brain tissue and its protective covering (the meninges) can then herniate, or push outward, through that gap. The size of the protrusion varies widely. Some encephaloceles are small enough to go unnoticed at birth, while others are large and immediately visible.
If the sac contains only the brain’s protective membranes and fluid, it’s sometimes called a meningocele. When actual brain tissue is involved, the condition is more serious because that displaced tissue is often abnormal or nonfunctional.
Types Based on Location
Encephaloceles are classified by where the skull opening occurs:
- Occipital: At the lower back of the head. This is the most common type in Western populations.
- Frontoethmoidal (sincipital): Near the forehead, between or behind the eyes. More common in parts of Southeast Asia.
- Parietal: At the top of the head, toward the back.
- Sphenoidal: Behind the eyes and in front of the ears. These are internal and not visible from the outside, making them harder to detect.
Doctors also use the broader terms “anterior” (front of the skull) and “posterior” (back of the skull). The location matters because it influences which brain structures are affected and, in turn, the severity of symptoms and the surgical approach.
Causes and Risk Factors
Both genetic and environmental factors play a role. No single cause has been identified, but several risk factors increase the likelihood of an encephalocele:
- Family history of neural tube defects: A previous pregnancy affected by any neural tube defect raises the risk for future pregnancies.
- Certain infections during pregnancy: Toxoplasmosis, rubella, cytomegalovirus, and herpes simplex virus have all been linked to cases.
- Genetic syndromes: Over 30 syndromes are associated with encephaloceles. The most well-known is Meckel-Gruber syndrome, a severe condition that also involves enlarged, cyst-filled kidneys and extra fingers or toes. Other associated syndromes include Walker-Warburg, Fraser, and Knobloch syndromes.
- Consanguinity: Parents who are closely related by blood have a higher chance of having a child with an encephalocele.
At the molecular level, several genetic signaling pathways involved in early brain development have been implicated, though the genetics are complex and not fully mapped. In many cases, no specific cause is ever identified.
How It’s Diagnosed
Most encephaloceles are found before birth. A routine prenatal ultrasound, typically performed between 11 and 14 weeks of pregnancy, can detect the defect. By 13 weeks, ultrasound can usually distinguish between a sac that contains only fluid and membranes versus one that contains brain tissue, an important distinction for planning care.
If ultrasound raises a concern, MRI provides a more detailed picture. It’s better at showing exactly what’s inside the sac, how the brain connects to the herniated tissue, and whether there are additional brain abnormalities. CT scans are sometimes used to map the bony defect in detail. Conditions that can look similar on imaging, such as cystic hygromas, dermoid cysts, and hemangiomas, need to be ruled out, and MRI is the most reliable tool for doing so.
Encephaloceles that are internal, particularly the sphenoidal type, may not be caught until later in childhood when symptoms like breathing problems, vision changes, or fluid leaking from the nose prompt further investigation.
Surgical Repair
Surgery is the primary treatment. The goals are straightforward: close the protective layer around the brain (the dura) so it’s watertight, repair the opening in the skull, and reconstruct any external bone deformity. If the herniated brain tissue is abnormal or nonfunctional, it’s removed during the procedure.
Timing depends on the child’s overall health. Repair is generally recommended within the first few months of life to prevent infection, breathing problems, and further neurological damage. However, many surgeons prefer to wait until the baby is 5 to 10 months old to reduce the risks of prolonged anesthesia in very young infants, particularly blood loss and difficulty maintaining body temperature. Urgent cases, such as those with a ruptured sac or breathing distress, are operated on sooner.
For frontoethmoidal encephaloceles near the forehead, early repair is especially important to prevent distortion of the facial bones as the child grows. The surgeon typically accesses the defect through an incision along the hairline, lifts the frontal bone, and repairs the opening from the inside. The skull gap is then reconstructed using either the child’s own bone or an artificial mesh made from titanium or similar materials.
Long-Term Outlook
The prognosis for a child with an encephalocele depends heavily on the size and location of the defect, how much brain tissue is involved, and whether other brain abnormalities or genetic syndromes are present. Small encephaloceles that contain mostly fluid and membranes tend to have the best outcomes. Children with these may develop normally or near-normally after surgical repair.
Larger encephaloceles involving significant amounts of brain tissue carry a higher risk of developmental delays, seizures, vision problems, and intellectual disability. Hydrocephalus, a buildup of fluid in the brain, is a common complication that may require additional treatment with a shunt to drain excess fluid. Occipital encephaloceles, because of their location near structures that control balance, coordination, and basic functions like breathing and swallowing, tend to have more serious neurological consequences than anterior types.
Children born with an encephalocele as part of a genetic syndrome like Meckel-Gruber generally face a more guarded prognosis, since the encephalocele is only one of several serious abnormalities affecting multiple organ systems.
Prevention With Folic Acid
Because encephalocele is a neural tube defect, folic acid supplementation before and during early pregnancy reduces the risk. The U.S. Preventive Services Task Force gives its strongest recommendation (Grade A) that anyone planning to or who could become pregnant take 400 to 800 micrograms of folic acid daily. This is the amount found in most over-the-counter prenatal vitamins and standard multivitamins.
The supplement is most effective when taken before conception, since the neural tube closes within the first four weeks of pregnancy, often before a person knows they’re pregnant. In countries that fortify grain products with folic acid, rates of neural tube defects, including encephaloceles, have declined, though the condition has not been eliminated entirely because not all cases are caused by folate deficiency.