What Causes Hydrocephalus in Newborns: 5 Main Reasons

By /
what causes hydrocephalus in newborns

By Haris Bin Tahir
Father of a hydrocephalus survivor. Independent researcher.
Founder, Brain Care Path · braincarepath.com

Quick answer: Hydrocephalus in newborns has five main causes: bleeding in the brain after premature birth, spina bifida and other neural tube defects, a narrowed drainage channel called aqueductal stenosis, infection, and rarely a tumour or an inherited genetic change. Which cause applies shapes both treatment and outlook.

Nobody uses the word at first. A midwife measures your baby’s head, writes the number down, then measures it again a week later and goes to find someone more senior. That gap, between the second measurement and the conversation that follows, is where most families first meet this condition. The question almost every parent asks in that conversation is the same one you are probably asking now: what causes hydrocephalus in newborns, and did we do something to cause it?

The short answer to the second half is no. Here is what I understand after two and a half years of living with this, reading the research, and asking the same questions you are asking.

Why Hydrocephalus Happens in a Newborn Brain

Cerebrospinal fluid (CSF) is made continuously inside the brain, circulates through four connected chambers called ventricles, and is absorbed back into the bloodstream. Hydrocephalus develops when that cycle fails and fluid accumulates, widening the ventricles and raising pressure. Researchers describe it as a failure of CSF homeostasis rather than simply “too much water” (Kahle et al., Nature Reviews Disease Primers, 2024).

Doctors sort the causes into two groups. Congenital hydrocephalus is present at or near birth. Acquired hydrocephalus develops afterwards, most often following bleeding or infection. This distinction matters, because it changes what your medical team watches for next. Below are the five causes behind the overwhelming majority of newborn cases.

1. Bleeding in the Brain After Premature Birth

This is the leading cause in babies born early. Fragile blood vessels in a premature brain can bleed into the ventricles, a condition called intraventricular haemorrhage (IVH). Blood and its breakdown products then interfere with normal fluid drainage and absorption.

IVH affects roughly 15–20% of infants born weighing under 1,500g. Furthermore, about 10% of all infants with IVH, and 20% of those with severe bleeds, develop progressive ventricular dilation needing surgical treatment (Cohen and Flibotte, Clinics in Perinatology, 2022). Therefore prematurity itself is not the cause; the bleed is. We cover the neonatal unit experience separately in hydrocephalus in premature babies.

intraventricular haemorrhage in a premature baby

2. Spina Bifida and Other Neural Tube Defects

When the spinal column does not close completely in early pregnancy, the brain is frequently affected too. Most children born with myelomeningocele, the most severe common form of spina bifida, also develop hydrocephalus. The link runs through an associated change in brain structure called Chiari II malformation, which obstructs fluid flow at the base of the brain.

Across a meta-analysis of 11,529 children in 18 Asian countries, hydrocephalus secondary to spinal dysraphism accounted for 7.6% of cases (Ferris et al., Journal of Neurosurgery: Pediatrics, 2024). We explain the mechanism in how hydrocephalus and spina bifida are connected. Additionally, encephalocele, a rarer neural tube defect, carries a similarly high association (Akyol et al., European Review, 2022).

3. A Blocked Drainage Channel: Aqueductal Stenosis

The cerebral aqueduct is a narrow channel carrying fluid between the third and fourth ventricles. Because it is the tightest point in the system, it blocks easily. Narrowing there is one of the most common causes of hydrocephalus present at birth, and doctors frequently pick it up on a routine prenatal ultrasound (Pindrik et al., Seminars in Pediatric Neurology, 2022).

Sometimes the narrowing is a malformation. Sometimes it follows scarring from earlier bleeding or infection. In a smaller group it is an inherited X-linked condition affecting mainly boys. Our guide to aqueductal stenosis and Dandy-Walker malformation covers both in plain language.

4. Infection, and Why Geography Changes the Answer

Infection of the central nervous system, particularly neonatal meningitis, can inflame and scar the membranes that absorb cerebrospinal fluid. Consequently fluid builds up, and doctors call the result post-infectious hydrocephalus.

Here the research says something most parent guides leave out. In that same Asian meta-analysis, post-infectious hydrocephalus accounted for 10.7% of paediatric cases overall, but 19.2% in lower-middle-income countries and 23.2% specifically in South Asia. Moreover, the proportion fell as a country’s Human Development Index and urbanisation rose (Ferris et al., 2024). In other words, where a child is born changes which cause is most likely. Western guidance treating infection as a rare cause does not describe the picture in Pakistan, India or Bangladesh. We write about recovery from this specific cause in post-infectious hydrocephalus.

5. Tumours and Genetic Causes

These are the least common, yet they do occur. A tumour can obstruct fluid pathways directly. Among infants diagnosed with a brain tumour, more than 70% have associated hydrocephalus, rising above 90% when the tumour sits at the back of the brain (Yengo-Kahn and Dewan, Child’s Nervous System, 2021).

Separately, researchers have now linked some congenital cases to specific gene mutations that disrupt how the brain forms (Kahle et al., 2024). Consequently teams offer genetic testing more often than they once did, particularly where there is no bleed, no infection and no structural explanation.

What the Research Shows About How Common This Is

Best current estimates put the incidence of infant hydrocephalus at between 80 and 125 cases per 100,000 births, varying by world region (Tamber, Child’s Nervous System, 2021). The mix of causes varies with it. Congenital malformations and post-haemorrhagic hydrocephalus dominate in high-income countries, while infection-related cases weigh far more heavily in lower-income regions.

One honest caveat belongs here. A large share of cases in the published data carry no clear cause at all, which the authors of the Asian meta-analysis flag directly as a gap in diagnosis and classification. So if your team has not given you a definite cause, nobody is keeping you in the dark. Sometimes the answer genuinely is not known.

What This Means for Your Family

The cause matters less than you might expect for the decision immediately in front of you, and more than you might expect for everything after it. Treatment of the pressure itself, whether by shunt or by endoscopic third ventriculostomy, follows the same logic regardless of cause.

However, the cause shapes the monitoring. A baby with post-haemorrhagic hydrocephalus is watched differently from one with spina bifida, and infection-related cases carry their own follow-up. So ask your team directly what they believe caused it, because that answer sets the shape of the next few years. Meanwhile our guide to signs and symptoms in newborns covers what to watch for at home.

Finally, this needs saying plainly: none of these causes are things a parent brings about. Not the bleed, not the malformation, not the infection.

Questions to Ask Your Doctor

  • What do you believe caused the hydrocephalus in our baby, and how confident are you?
  • Was this present before birth, or did it develop afterwards?
  • If a bleed caused it, which grade was the haemorrhage?
  • Is genetic testing appropriate in our case, and what would it change?
  • Does the cause change how often our baby needs scans or reviews?
  • Does the cause affect the choice between a shunt and an ETV?
  • Is there anything about the cause that affects risk in a future pregnancy?

Frequently Asked Questions About Hydrocephalus in Newborns

What is the most common cause of hydrocephalus in newborns?

It depends on where the baby is born. In high-income countries, bleeding into the ventricles after premature birth is the leading cause. In South Asia and other lower-middle-income regions, infection of the central nervous system accounts for a far larger share, close to one case in four.

Can anything a mother does during pregnancy cause hydrocephalus in a newborn?

No. The established causes are haemorrhage, neural tube defects, structural narrowing, infection, tumours and genetic change. None result from ordinary maternal behaviour. Adequate folic acid before and during early pregnancy does reduce the risk of neural tube defects, which is a point about prevention rather than blame.

Is hydrocephalus in newborns genetic?

Usually not, but sometimes. Researchers have linked some congenital cases to gene mutations that disrupt brain development, and X-linked aqueductal stenosis affects mainly boys. Most cases have a structural or acquired cause instead. Ask whether genetic testing is appropriate in your case.

Can hydrocephalus in a newborn be detected before birth?

Often, yes. Sonographers frequently see both aqueductal stenosis and neural tube defects on routine prenatal ultrasound, usually from the second trimester, and a more detailed fetal MRI confirms it. Post-haemorrhagic and post-infectious causes, by their nature, appear after birth.

That week between the two measurements was the longest week we had. What nobody told us then, and what I would want someone to tell you now, is that the cause is a piece of information rather than a verdict. It tells your team where to look and what to watch. It does not tell you who your child will become. Ask the question, write down the answer, then go and hold your baby.

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

Further reading: the NHS overview of hydrocephalus.

Scroll to Top

In Collaboration With

Partner hospitals and institutions will appear here as collaborations begin.