[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Embryology](https://durgical.com/en/embryology/) › [Nervous system and senses](https://durgical.com/en/embryology/#a-nervous) › Congenital hydrocephalus: aqueductal stenosis [Embryology](https://durgical.com/en/embryology/) · [Nervous system and senses](https://durgical.com/en/embryology/#a-nervous) # 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](https://durgical.com/en/anatomy/aqueduct-of-midbrain/) · [Lateral ventricles](https://durgical.com/en/anatomy/lateral-ventricle/) · [Third ventricle](https://durgical.com/en/anatomy/third-ventricle/) · [Fourth ventricle](https://durgical.com/en/anatomy/fourth-ventricle/) · [Choroid plexus](https://durgical.com/en/anatomy/choroid-plexus/) ## Key points - Most common cause of congenital hydrocephalus: aqueductal stenosis. - Dilated lateral + third with a normal fourth = block at the aqueduct. - X-linked L1CAM: adducted thumbs. - Sunset sign and bulging fontanelle. - Third ventriculostomy works for aqueductal obstruction. ## 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. ## Memory aid The aqueduct is 'the bottleneck': cork it and everything upstream fills while everything downstream stays empty. ## 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). [Add to my cards (3)](https://durgical.app/estudiar/?add=/en/embryology/congenital-hydrocephalus-aqueductal-stenosis/) ## See it in 3D The structures of Durgical's 3D anatomy where it is found. - [Cerebral aqueduct](https://durgical.com/en/anatomy/aqueduct-of-midbrain/) - [Lateral ventricles](https://durgical.com/en/anatomy/lateral-ventricle/) - [Third ventricle](https://durgical.com/en/anatomy/third-ventricle/) - [Fourth ventricle](https://durgical.com/en/anatomy/fourth-ventricle/) - [Choroid plexus](https://durgical.com/en/anatomy/choroid-plexus/) ## Related - [Ventricles and cerebrospinal fluid](https://durgical.com/en/embryology/ventricles-and-cerebrospinal-fluid/) - [Brain vesicles: from three to five and what each becomes](https://durgical.com/en/embryology/brain-vesicles-from-three-to-five-and-what-each-becomes/) - [Chiari malformations](https://durgical.com/en/embryology/chiari-malformations/) - [Dandy–Walker malformation](https://durgical.com/en/embryology/dandy-walker-malformation/) - [Neural tube defects: anencephaly, spina bifida and encephalocele](https://durgical.com/en/embryology/neural-tube-defects-anencephaly-spina-bifida-and-encephalocele/) - [TORCH infections: what each agent does to the embryo and fetus](https://durgical.com/en/embryology/torch-infections-what-each-agent-does-to-the-embryo-and-fetus/) ## Related conditions - [Hydrocephalus](https://durgical.com/en/conditions/hydrocephalus/) - [Congenital (TORCH) infections: syphilis, toxoplasmosis, CMV and Zika](https://durgical.com/en/conditions/congenital-infections-syphilis-toxoplasmosis-cmv-and-zika/) ## Microorganisms - [Toxoplasma gondii](https://durgical.com/en/microbiology/toxoplasma-gondii/) - [Cytomegalovirus](https://durgical.com/en/microbiology/cytomegalovirus/) [← All of embryology](https://durgical.com/en/embryology/) 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](https://www.ninds.nih.gov/health-information/disorders/hydrocephalus) (National Institute of Neurological Disorders and Stroke, 2024); [Hydrocephalus: MedlinePlus Medical Encyclopedia](https://medlineplus.gov/ency/article/001571.htm) (U.S. National Library of Medicine, 2024); Langman's Medical Embryology, 13th ed., ch. 18: Central Nervous System (Wolters Kluwer, 2015). ## **Spotted a mistake?** We are always improving for the community. Tell us what is wrong and our team will review it. Report a mistake Representative model, for educational purposes only. --- Source: https://durgical.com/en/embryology/congenital-hydrocephalus-aqueductal-stenosis/ License: CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/). Cite as: DurgiPedia (durgical.com), https://durgical.com/en/embryology/congenital-hydrocephalus-aqueductal-stenosis/