Embryology · Nervous system and senses
Congenital hydrocephalus: aqueductal stenosis !
- Malformation
Fluid cannot leave the brain's ventricles, so it builds up and enlarges the baby's head, whose sutures are still open.
Updated 2026-11-01
See it in 3D: Cerebral aqueduct · Lateral ventricles · Third ventricle · Fourth ventricle · Choroid plexus
What it is
Congenital hydrocephalus is an abnormal build-up of CSF in the ventricles present from before birth. In the newborn the most common cause is narrowing or blockage of the cerebral aqueduct; others are Chiari II with myelomeningocele, Dandy–Walker, prenatal infections and bleeding in preterm babies. Because the sutures have not fused, the head grows.
Key facts
- The aqueduct (lumen of the midbrain) is the narrowest part of the ventricular system.
- Aqueductal stenosis: dilated lateral and third ventricles, normal fourth.
- An X-linked form from L1CAM mutations: boys with adducted thumbs.
- Prenatal infections (toxoplasmosis, CMV, rubella) can cause stenosis through inflammation.
- It is common in children with myelomeningocele (Chiari II).
Embryological cause
- The aqueduct fails to form at its normal calibre (stenosis, forking or a membrane) or closes by gliosis after infection or bleeding.
- CSF made by the choroid plexuses of the lateral and third ventricles is trapped above the aqueduct.
- The ventricles dilate, thin the cortex and spread the still-open skull sutures.
Markers
- L1CAM
How it presents
- Macrocephaly or a head circumference crossing centiles; bulging, tense anterior fontanelle.
- Split sutures, prominent scalp veins.
- Downward gaze ('sunset eyes'), irritability, vomiting, sleepiness, seizures.
- Delayed or lost developmental milestones.
Diagnosis
- Prenatal: ventriculomegaly on ultrasound; fetal MRI for the cause.
- Infant: cranial ultrasound through the fontanelle first; MRI for detail.
- Serial head circumference measurements.
- Treatment: ventriculoperitoneal shunt or endoscopic third ventriculostomy.
Test yourself
Think of the answer, then tap the question to see it.
What is the most common cause of hydrocephalus in the newborn?
Stenosis or obstruction of the cerebral aqueduct.
Which ventricles dilate in aqueductal stenosis?
The lateral and third ventricles; the fourth stays normal in size.
Which gene causes X-linked hydrocephalus, and which hand sign suggests it?
L1CAM; adducted thumbs (flexed across the palm).
See it in 3D
The structures of Durgical's 3D anatomy where it is found.
Related
- Ventricles and cerebrospinal fluid
- Brain vesicles: from three to five and what each becomes
- Chiari malformations
- Dandy–Walker malformation
- Neural tube defects: anencephaly, spina bifida and encephalocele
- TORCH infections: what each agent does to the embryo and fetus
Related conditions
Microorganisms
Educational content on embryonic development; not a guide to prenatal diagnosis or to medicines in pregnancy and no substitute for a health professional's advice. No doses are given.
Sources: Hydrocephalus (National Institute of Neurological Disorders and Stroke, 2024); Hydrocephalus: MedlinePlus Medical Encyclopedia (U.S. National Library of Medicine, 2024); Langman's Medical Embryology, 13th ed., ch. 18: Central Nervous System (Wolters Kluwer, 2015).
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Representative model, for educational purposes only.