To understand encephalocele, it helps to first understand how a baby's brain and skull are supposed to form.
The neural tube: the brain and spinal cord's starting point
Very early in pregnancy — around the third and fourth weeks, often before a pregnancy is confirmed — a flat sheet of cells folds over on itself and zips closed into a hollow structure called the neural tube. The top of this tube becomes the brain; the rest becomes the spinal cord.
This "zipping" has to happen completely and on time. When the tube closes properly, the brain and spinal cord can develop inside their protective bony shells: the skull and the spine.
When closure is incomplete
If part of the neural tube — specifically the part destined to become the skull — does not close fully, the bone that should cover the brain in that spot doesn't form completely either. That leaves a gap in the skull. Through that gap, the membranes covering the brain (and sometimes brain tissue) can bulge outward, forming an encephalocele.
In other words, an encephalocele is not the brain "growing wrong" later — it traces back to a closure step that happens in the first month.
Sutures, fontanelles, and the difference from craniosynostosis
Parents sometimes confuse encephalocele with craniosynostosis, but they are very different:
- Sutures are the flexible seams between the skull bones, and fontanelles are the "soft spots." They let the skull grow with the brain.
- Craniosynostosis is when a suture closes too early, changing head shape.
- Encephalocele is a different problem entirely — a gap where the skull and the layers beneath it never closed, allowing tissue to herniate out.
Why the location varies
Because the neural tube and skull form along the midline, encephaloceles tend to appear along that center line — back of the head, top of the head, or between the eyes and nose. Where the closure problem occurs influences both the type of encephalocele and a great deal about the outlook.
Sources
- NINDS / NIH — Neural Tube Defects information
- CDC — Encephalocele (Birth Defects)
- Boston Children's Hospital — Encephaloceles
- StatPearls (NCBI Bookshelf) — Encephalocele