Quick answer: Most children born with myelomeningocele, the most common and severe form of spina bifida, also develop hydrocephalus — largely because of an associated brain structure change called Chiari II malformation. Studies report hydrocephalus in roughly 70-80% of myelomeningocele cases, most requiring a shunt or ETV in infancy.
Parents in spina bifida groups often arrive already fluent in one diagnosis and then get blindsided by a second. That was not our exact path — our son’s hydrocephalus arrived alone — but I have sat in enough waiting rooms with spina bifida families to know how often the two conditions travel together, and how rarely anyone explains why before the second diagnosis lands.
What Spina Bifida Actually Is, Briefly
Spina bifida is a neural tube defect where the spinal column does not close completely during early pregnancy, most often around three to four weeks’ gestation. Myelomeningocele is the most severe and most common form requiring treatment, in which the spinal cord and its coverings protrude through the opening in a visible sac, typically in the lower back. It is distinct from milder forms like spina bifida occulta, which frequently causes no symptoms at all.
Why Hydrocephalus Shows Up So Often Alongside It
The connection runs through a specific structural change called Chiari II malformation, in which parts of the cerebellum and brainstem are pulled downward into the spinal canal. This shift can obstruct normal cerebrospinal fluid flow at the base of the brain, leading directly to hydrocephalus. According to PubMed, a 2026 retrospective review of 176 confirmed spina bifida spectrum cases at a major referral hospital found hydrocephalus present in 71% of cases overall, with myelomeningocele the most prevalent diagnosis at 77.8% of the cohort (Engidaw et al., Child’s Nervous System, 2026). In that same cohort, 25% of patients required ventriculoperitoneal shunt insertion and a further 5.4% underwent endoscopic third ventriculostomy.
Does Fetal Surgery Change the Picture?
It can, meaningfully. Fetal repair of myelomeningocele — surgery performed before birth, generally between 19 and 26 weeks’ gestation — has become standard of care for appropriately selected pregnancies since the landmark MOMS trial. According to PubMed, a 2025 analysis of 333 myelomeningocele and myeloschisis patients found that fetal repair significantly reduced the rate of permanent CSF diversion compared with postnatal closure — 27.8% versus 70.1% — and also delayed the onset of clinical hydrocephalus considerably, 24.2 weeks of age versus 2.8 weeks (Kundishora et al., Child’s Nervous System, 2025). That is not a guarantee against hydrocephalus, but it is a substantially different set of odds than postnatal repair alone offers.
What Doctors Watch For After Birth
Whether or not fetal surgery was performed, infants with myelomeningocele are closely monitored for hydrocephalus signs in the newborn period and beyond: rapid head circumference growth, a bulging fontanelle, downward-deviated eyes (“sunsetting”), increased irritability, and vomiting. Head circumference tracking is done at essentially every visit for the first year, because in this population it is one of the most sensitive early indicators available.
What This Means for Your Family
If your child has myelomeningocele and has not yet developed hydrocephalus, ongoing surveillance does not mean something is expected to go wrong — it means the connection between the two conditions is well-established enough that catching early signs matters more than in the general population. If your child already has both diagnoses, the treatment principles for the hydrocephalus itself — shunt versus ETV, monitoring for shunt malfunction — largely follow the same guidance as hydrocephalus from any other cause, layered on top of the orthopedic, urological, and mobility care spina bifida itself requires.
Questions to Ask Your Doctor
- Does my child’s imaging show Chiari II malformation, and how is that being monitored separately from the hydrocephalus itself?
- If fetal surgery was performed, does that change our hydrocephalus monitoring schedule going forward?
- What head circumference growth rate would trigger further imaging?
- How does having both spina bifida and hydrocephalus affect the choice between ETV and a shunt?
- Which specialist — neurosurgery or the spina bifida clinic team — should we contact first if we notice new symptoms?
Frequently Asked Questions About Hydrocephalus and Spina Bifida
Do all children with spina bifida develop hydrocephalus?
No, but most children with myelomeningocele specifically do — studies report roughly 70-80% of cases. Milder forms of spina bifida, like spina bifida occulta, rarely involve hydrocephalus at all.
What is Chiari II malformation?
It is a structural change in which the cerebellum and brainstem are displaced downward into the spinal canal, commonly associated with myelomeningocele, and it is the primary reason hydrocephalus develops so frequently alongside spina bifida.
Can fetal surgery prevent hydrocephalus entirely?
Not entirely, but research shows fetal repair significantly reduces the rate of permanent shunt or CSF diversion need compared with surgery performed after birth.
Is the hydrocephalus treatment different because a child also has spina bifida?
The core treatment options — shunt or ETV — are generally the same, though the overall care plan is coordinated more closely with a multidisciplinary spina bifida team.
I think often about how much earlier some of the spina bifida families I know might have caught certain symptoms if someone had simply explained the Chiari connection to them plainly, on day one, rather than assuming they would piece it together from a discharge packet. If that is you right now, you did not miss anything by not already knowing this. You are finding out now.
This article is written for informational purposes only and does not constitute medical advice. Always consult your neurologist, paediatrician, or qualified healthcare provider for diagnosis and treatment decisions specific to your child’s situation. Read our full medical disclaimer at braincarepath.com/disclaimer/
Bibliography
- Engidaw EA, Tefera EA, Bekele KM, Belayneh EM, Gebrehiwet CL, Molla YD. Surgical treatment and outcomes of neural tube defects at the University of Gondar Comprehensive Specialized Hospital, Ethiopia: a two-year retrospective review. Child’s Nervous System. 2026;42(1). Available at: https://doi.org/10.1007/s00381-026-07411-9
- Kundishora AJ, Bond K, Rosenfeld M, et al. Detailed analysis of hydrocephalus patterns and associated variables in patients after open fetal repair and postnatal myelomeningocele/myeloschisis closure. Child’s Nervous System. 2025;41(1):160. Available at: https://doi.org/10.1007/s00381-025-06819-z
- Spina Bifida Association. Hydrocephalus and Spina Bifida. Available at: https://www.spinabifidaassociation.org/