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Brain

Ventricular System

The ventricular system consists of interconnected cavities within the brain that produce, transport, and store cerebrospinal fluid (CSF), which cushions the brain and spinal cord. Below is a brief overview of the ventricles and their key features.


Lateral Ventricles

  • Parts:
    • Frontal horn: Located anteriorly, extending into the frontal lobe.
    • Body: Positioned in the parietal lobe.
    • Atrium (Trigone): Junction of the body, occipital horn, and temporal horn; a common site for choroid plexus calcifications.
    • Occipital horn: Extends into the occipital lobe.
    • Temporal horn: Extends into the temporal lobe.
  • Connections:
    • Foramina of Monro: Paired openings that connect the frontal horns of the lateral ventricles to the third ventricle. Obstruction here can lead to hydrocephalus.

Third Ventricle

  • Description:
    • A midline structure located between the thalami.
    • Plays a crucial role in CSF circulation as a central passage point.
  • Connections:
    • Foramina of Monro: Receives CSF from the lateral ventricles.
    • Cerebral aqueduct (Aqueduct of Sylvius): A narrow posterior midline channel connecting the third ventricle to the fourth ventricle. It is a common site for obstruction, leading to aqueductal stenosis.

Fourth Ventricle

  • Description:
    • Located in the posterior fossa, bordered anteriorly by the brainstem and posteriorly by the cerebellum.
    • Serves as a final reservoir for CSF before it enters the subarachnoid space.
  • Connections:
    • Cerebral aqueduct: Superior midline input from the third ventricle.
    • Foramen of Magendie: A posterior midline opening that allows CSF to flow into the cisterna magna.
    • Foramina of Luschka: Paired lateral openings that direct CSF into the prepontine cisterns.
    • Obex: The inferior midline point where the fourth ventricle transitions into the central canal of the spinal cord.

Choroid Plexus

  • Function:
    • Specialized tissue that produces CSF by filtering blood plasma. It also helps maintain intracranial pressure and nutrient balance.
  • Locations:
    • Prominent in the atrium of the lateral ventricles, extending into the posterior part of the temporal horns.
    • Found in the roof of the fourth ventricle and less prominently in the roof of the third ventricle.

CSF Flow Summary

In normal physiology, CSF flows unidirectionally through the ventricular system:

Lateral Ventricles

Third Ventricle

Fourth Ventricle

Subarachnoid Spaces (including basal cisterns)

Venous sinuses (absorption via arachnoid granulations)


Clinical Relevance

  • Hydrocephalus: Blockages at any point in the ventricular system (e.g., foramina of Monro, cerebral aqueduct) can cause increased CSF pressure, leading to ventricular dilation.
  • Choroid plexus tumors: Rare but can cause overproduction of CSF.
  • Infections: Conditions like meningitis can impact CSF flow and absorption. For example, exudates can block narrow passages like the various foramina, causing obstructive hydrocephalus. Alternatively, meningitis can damage the arachnoid granulations, reducing absorption. Rarely, inflammation of the choroid plexus can result in overproduction of CSF.

A clear understanding of the ventricular anatomy and CSF dynamics is critical for diagnosing and managing neurological disorders.