CSF, Ventricles & Brain Anatomy
Cerebral aqueduct (aqueduct of Sylvius)
The cerebral aqueduct is the narrow channel connecting the third and fourth ventricles, and a common site of blockage in hydrocephalus.
In short: Cerebral aqueduct (aqueduct of Sylvius)
- It is the narrowest part of the ventricular system.
- Narrowing here (aqueductal stenosis) is a common cause of obstructive hydrocephalus.
- A blockage here causes the lateral and third ventricles to enlarge.
- It is often bypassed by ETV.
What it is
The cerebral aqueduct (also called the aqueduct of Sylvius) is a thin channel that carries CSF from the third ventricle down to the fourth ventricle. It is the narrowest point in the ventricular system.
Understanding Cerebral aqueduct (aqueduct of Sylvius)
Because it is so narrow, the cerebral aqueduct is especially prone to blockage. Narrowing or obstruction here — aqueductal stenosis — is one of the most common causes of obstructive hydrocephalus, particularly congenital forms. When the aqueduct is blocked, fluid backs up and enlarges the lateral and third ventricles while the fourth ventricle stays normal (the triventricular pattern). This type of blockage is frequently treated with endoscopic third ventriculostomy (ETV), which creates a new outlet to bypass the aqueduct.
Why it matters
Understanding the cerebral aqueduct helps families see why this narrow channel is a frequent site of blockage, how that produces a recognizable pattern of enlarged ventricles, and why ETV is often used to bypass it.
Common questions
What does the cerebral aqueduct connect?
The third and fourth ventricles.
Why is it prone to blockage?
It is the narrowest part of the ventricular system.
How is a blockage here treated?
Often with ETV, which bypasses it.
Bottom line
The cerebral aqueduct is the narrow channel between the third and fourth ventricles, a common blockage site often bypassed by ETV.
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