Dr Željko Kojadinović — NEUROHIRURGIJA I LEČENJE BOLA
Dr Zeljko Kojadinovic — Pain Treatment & Neurosurgery
Author:
Dr. Zeljko Kojadinovic, MD, PhD
— Neurosurgeon and Pain Management Specialist
Specialized Experience:
30 years of clinical expertise in neurosurgery
Last medically reviewed:
January 8, 2026
What are the brain ventricles?
The ventricles are a connected system of fluid-filled spaces inside the brain. They contain cerebrospinal fluid (CSF). The ventricles are normal anatomy — everyone has them.
There are four main parts.
Lateral ventricles (right and left)
These are the largest ventricles. They sit deep inside each cerebral hemisphere. Lateral ventricles connect to the third ventricle through the interventricular foramina (Foramina of Monro)
Third ventricle
A narrow midline cavity between the two halves of the brain, near the thalamus.
Cerebral aqueduct (Aqueduct of Sylvius)
A small channel that connects the third ventricle to the fourth ventricle. Because it is narrow, it can become a bottleneck if CSF flow is disturbed.
Fourth ventricle
Located between the brainstem and the cerebellum. From here, CSF normally reaches the fluid spaces around the brain and spinal cord.
Image: Ventricles of the brain (lateral, 3rd, and 4th) and the communications between them (foramen of Monro and the aqueduct of Sylvius).
What is cerebrospinal fluid (CSF)?
CSF is a clear fluid that surrounds the brain and spinal cord and also fills the ventricles. It is continuously produced and continuously absorbed.
In adults, the total amount of CSF is relatively small, but it is renewed throughout the day. CSF problems are therefore usually related to flow and pressure balance, not to a lack of fluid.
Where does CSF come from?
Most CSF is produced by the choroid plexus, a specialized tissue located inside the ventricles, especially in the lateral ventricles.
Image: Cerebrospinal fluid (CSF) flow: from production within the ventricles, circulation through the ventricular system, and exit into the subarachnoid space, where it flows before being resorbed into the venous system (specifically the dural venous sinuses).
What does CSF do?
CSF has several key roles.
- It cushions and protects the brain and spinal cord.
- It helps maintain a stable environment for nervous system function.
- It supports clearance of metabolic waste.
- It contributes to regulation of pressure inside the skull.
How CSF circulates
CSF is produced mainly in the lateral ventricles. It flows through the ventricular system toward the third ventricle, then passes through the cerebral aqueduct into the fourth ventricle.
From the fourth ventricle, CSF enters the subarachnoid space around the brain and spinal cord. It is then absorbed back into the bloodstream through structures called arachnoid granulations.
This circulation is continuous and works only if production, flow, and absorption remain in balance. The total volume of CSF is approximately 150–180 ml. This entire volume is produced in the choroid plexuses and resorbed into the dural venous sinuses, renewing itself three to four times daily. (About 500 ml of CSF is produced every day.)
Why enlarged ventricles can mean different things
When imaging reports mention ventricular enlargement or ventriculomegaly, this does not automatically point to a single diagnosis.
Ventricles may appear enlarged because of:
- disturbed CSF circulation or absorption (hydrocephalus),
- loss of brain tissue volume over time (so-called ex vacuo enlargement),
- normal anatomical variation without symptoms.
Correct interpretation always depends on symptoms, neurological examination, and detailed imaging findings.
Why symptoms depend on pressure, not size alone
Symptoms correlate more closely with CSF pressure dynamics and brain function than with ventricle size by itself.
Two people may have similarly sized ventricles on imaging, yet only one develops symptoms. This is why imaging findings are always interpreted in clinical context.
Why the location of blockage matters
If CSF flow is impaired, the pattern of ventricular enlargement can suggest where the problem lies.
Blockage at different points in the ventricular system affects different compartments upstream. This anatomical logic helps guide interpretation of imaging studies. If the blockage is inside the ventricular system, it is called obstructive hydrocephalus; if the problem is in the absorption of fluid outside the ventricles, it is known as communicating hydrocephalus.
Common terms you may see in reports
Ventriculomegaly – ventricles appear enlarged; not a diagnosis by itself.
Hydrocephalus – ventricular enlargement caused by disturbed CSF flow or absorption.
Subarachnoid space – CSF space around the brain and spinal cord.
Choroid plexus – tissue inside ventricles that produces most CSF.
Cerebral aqueduct – narrow channel connecting the third and fourth ventricles.
When this anatomy becomes clinically important
Understanding ventricles and CSF is particularly important when imaging or clinical notes mention hydrocephalus, increased intracranial pressure, subarachnoid hemorrhage, intraventricular blood with EVD, tumors or cysts near CSF pathways, or CSF diversion systems such as shunts or drains.