Fluid space
Cerebral aqueduct
Also called Aqueduct of Sylvius, Mesencephalic duct
A narrow canal through the midbrain that links the third and fourth ventricles.
The cerebral aqueduct is a thin channel running through the midbrain. It carries cerebrospinal fluid down from the third ventricle to the fourth. It is the narrowest part of the whole fluid system, which also makes it the easiest place for a blockage to happen. Around it lies a ring of gray matter that helps control pain and defensive reactions.
Where it is
Running through the middle of the midbrain, just in front of the four small bumps on its back, called the colliculi.
What it does
Connecting chambers
It is the only route for fluid from the upper ventricles to reach the fourth ventricle.
Pulsing flow
Fluid moves back and forth through it with each heartbeat, with an overall flow downward.
Surrounded by a pain control center
The gray matter wrapped around it, called the periaqueductal gray, can switch on the body's own pain relief.
Defense reactions
That same surrounding gray matter helps produce freezing, fleeing or fighting when you face danger.
Think of it as the thin neck of an hourglass: everything has to pass through it, and a tiny blockage stops the flow.
Works with
- Third ventricleIt receives fluid from the third ventricle at its upper end.
- Fourth ventricleIt empties into the fourth ventricle at its lower end.
- MidbrainIt tunnels right through the midbrain, surrounded by its tissue.
- Superior colliculusThe superior colliculi, which help steer your eyes, sit just behind its upper part.
- Centromedial amygdalaThe amygdala's output nuclei signal the gray matter around it to trigger freezing when you are afraid.
When it goes wrong
Aqueductal stenosis
If the aqueduct is too narrow or blocked, whether from birth, an infection or a tumor, fluid backs up. The lateral and third ventricles swell while the fourth stays normal, a telltale sign on scans.
Treatment
Surgeons can place a shunt to drain the extra fluid, or make a small opening in the floor of the third ventricle so fluid can bypass the blocked aqueduct.
For learning only, not medical advice. If you have a health concern, talk to a doctor.
Surprising facts
- Narrowing of the aqueduct is one of the most common causes of hydrocephalus in babies.
- Using special MRI scans, doctors can watch fluid pulse back and forth through it in time with the heartbeat.
- In a famous 1969 experiment, electrically stimulating the gray matter around the aqueduct blocked pain in some rats so well that surgery could be done without any other anesthetic.
By the numbers
Where the name comes from
"Aqueduct" comes from the Latin "aquae ductus", meaning a channel for water, like the famous Roman aqueducts. Its other name is usually traced to Franciscus Sylvius, a 17th-century Dutch doctor and anatomist, though it is unclear when the name first appeared.
Learn it in a lesson
- Wiring and fluidWhite matter cables and the ventricles. A short guided lesson in 3D.
Quick quiz
3 questions. Your answers are saved and come back in your daily review.
Which of these is a job of the cerebral aqueduct?
Show the answer
Connecting chambers. It is the only route for fluid from the upper ventricles to reach the fourth ventricle.
Connecting chambers. It is the only route for fluid from the upper ventricles to reach the fourth ventricle.
The cerebral aqueduct is part of which larger structure?
Show the answer
Ventricular system. It belongs to the ventricular system.
Ventricular system. It belongs to the ventricular system.
Which part fits this description? "Like the thin neck of an hourglass: everything has to pass through it, and a tiny blockage stops the flow."
Show the answer
Cerebral aqueduct. It is the cerebral aqueduct. A narrow canal through the midbrain that links the third and fourth ventricles.
Cerebral aqueduct. It is the cerebral aqueduct. A narrow canal through the midbrain that links the third and fourth ventricles.
These parts now come back in your daily review, just before you would forget them.
Practice it and its neighbors in 3DSources
- Neuroanatomy, Cerebral Aqueduct (Sylvian), StatPearls, NCBI Bookshelf
- Cerebral aqueduct (of Sylvius), Radiopaedia
- Neuroanatomy, Periaqueductal Gray, StatPearls, NCBI Bookshelf
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Explore the cerebral aqueduct in 3D
Turn it around, zoom inside and see how it connects to the rest of the brain, then test yourself with quick quizzes.
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