Anatomy chapters
Ventricular system and CSF
The four ventricles and the channels joining them, how cerebrospinal fluid is made, circulates and is absorbed, and the types of hydrocephalus that follow when it is blocked.
- CSF is made mainly by the choroid plexus, about 500 mL a day, with about 130–150 mL in the system at any time.
- Flow: lateral ventricles → interventricular foramina → third ventricle → cerebral aqueduct → fourth ventricle → Magendie and Luschka → subarachnoid space.
- It is absorbed into the superior sagittal sinus through arachnoid granulations; a block anywhere causes hydrocephalus.
On this page
Overview
The brain contains four connected cavities called ventricles. They are filled with cerebrospinal fluid (CSF), which also surrounds the brain and spinal cord in the subarachnoid space.
CSF cushions the brain, makes it effectively lighter (it floats), removes waste and helps keep a stable chemical environment.
The ventricles
Lateral ventricles
One in each cerebral hemisphere, C-shaped. Each has a body, an anterior horn (frontal lobe), a posterior horn (occipital lobe) and an inferior horn (temporal lobe).
They open into the third ventricle through the interventricular foramina (of Monro).
Third ventricle
A narrow slit in the midline between the two thalami. Its floor is formed by the hypothalamus.
It leads backwards into the cerebral aqueduct.
Cerebral aqueduct (of Sylvius)
A narrow channel through the midbrain, joining the third and fourth ventricles. It is the narrowest part of the system.
Fourth ventricle
A tent-shaped cavity between the pons and medulla in front and the cerebellum behind. Its floor is the rhomboid fossa.
CSF leaves it through three openings into the subarachnoid space:
- Median aperture (foramen of Magendie): one, in the roof, into the cisterna magna.
- Two lateral apertures (foramina of Luschka): at the sides.
It continues below as the central canal of the spinal cord.
A widely used memory aid: Magendie is Medial (midline); Luschka is Lateral.
Production of CSF
CSF is made mainly by the choroid plexuses, tufts of capillaries covered by specialised ependymal cells. They are found in the lateral, third and fourth ventricles. The largest is in the lateral ventricles.
- About 500 mL is made each day.
- About 130–150 mL is in the system at any time, so it is replaced several times a day.
- Normal pressure (lying on the side) is about 60–150 mm of water.
CSF is clear and colourless, with very little protein and very few cells.
Circulation of CSF
- Lateral ventricles
- → interventricular foramina (Monro) →
- Third ventricle
- → cerebral aqueduct (Sylvius) →
- Fourth ventricle
- → foramina of Magendie and Luschka →
- Subarachnoid space (around the brain and down around the cord)
- → absorbed through arachnoid granulations into the superior sagittal sinus (venous blood).
CSF is absorbed mainly through the arachnoid villi and granulations, which project into the superior sagittal sinus.
Subarachnoid cisterns
In some places the subarachnoid space is wide. These are cisterns.
- Cisterna magna (cerebellomedullary cistern): between the cerebellum and the medulla. The largest.
- Interpeduncular cistern: in front of the midbrain, containing the circle of Willis.
- Lumbar cistern: below the end of the cord (L2 to S2), containing the cauda equina; used for lumbar puncture.
Barriers
- Blood-brain barrier: formed mainly by tight junctions between the endothelial cells of brain capillaries.
- Blood-CSF barrier: formed by tight junctions between the choroid plexus epithelial cells.
These barriers keep many drugs and toxins out of the brain.
Clinical relevance
Hydrocephalus
An abnormal build-up of CSF with enlargement of the ventricles.
| Type | Cause | Example |
|---|---|---|
| Non-communicating (obstructive) | Block within the ventricular system | Aqueductal stenosis, tumour near the fourth ventricle, Dandy-Walker malformation |
| Communicating | Block in the subarachnoid space or failure of absorption | After meningitis or subarachnoid haemorrhage (scarring of arachnoid granulations) |
In aqueductal stenosis, the lateral and third ventricles enlarge but the fourth ventricle stays normal.
In communicating hydrocephalus, CSF can still pass from the ventricles into the subarachnoid space; the problem is absorption.
Hydrocephalus in infants
How it happens: CSF builds up before the skull sutures have fused.
What you see: an enlarging head, a tense bulging anterior fontanelle, separated sutures, and eyes turned downwards ("sunset sign").
Raised pressure in adults
How it happens: the skull cannot expand.
What you see: headache, vomiting, blurred vision and papilloedema (swelling of the optic disc). A lumbar puncture is dangerous if there is a mass, because it can cause brain herniation through the foramen magnum.
Normal pressure hydrocephalus
How it happens: in older adults, CSF absorption is reduced; pressure is intermittently raised.
What you see: the triad of walking difficulty, urinary incontinence and dementia.
"Wet, wobbly and wacky": incontinence, unsteady gait and confusion.
Treatment
A ventriculoperitoneal shunt drains CSF from a lateral ventricle to the peritoneal cavity.
Questions ask for the channel between two ventricles, the openings of the fourth ventricle, where CSF is made and absorbed, the daily volume, the cause of non-communicating hydrocephalus and which ventricles enlarge, and the triad of normal pressure hydrocephalus.
Quick revision
- Lateral ventricles → foramina of Monro → third ventricle.
- Third ventricle → cerebral aqueduct → fourth ventricle.
- Fourth ventricle → Magendie (median) and Luschka (lateral) → subarachnoid space.
- Choroid plexus makes about 500 mL a day; about 130–150 mL present.
- Absorbed by arachnoid granulations into the superior sagittal sinus.
- Aqueductal stenosis: lateral and third ventricles dilate; fourth normal.
- Normal pressure hydrocephalus: gait, incontinence, dementia.
Written by The House Job from standard neuroanatomy references (Snell's Clinical Neuroanatomy).
FAQ
Where is CSF produced?
Mainly by the choroid plexuses in the lateral, third and fourth ventricles.
Where is CSF absorbed?
Through the arachnoid granulations into the superior sagittal sinus.
What joins the third and fourth ventricles?
The cerebral aqueduct (of Sylvius) in the midbrain.
What is the commonest cause of congenital hydrocephalus?
Narrowing of the cerebral aqueduct (aqueductal stenosis).