Human Anatomy
Ventricular System of the Brain
Ventricular system anatomy for MBBS: lateral, third and fourth ventricles, their communications, choroid plexus and the basis of hydrocephalus, mapped to NMC codes AN63.1 and AN63.2.
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Ventricular System of the Brain
Ventricular system anatomy for MBBS: lateral, third and fourth ventricles, their communications, choroid plexus and the basis of hydrocephalus, mapped to NMC codes AN63.1 and AN63.2.
This chapter describes the parts, boundaries and communications of the four ventricles and the choroid plexus that secretes cerebrospinal fluid. It provides the anatomical basis for congenital and acquired hydrocephalus.
High-yield: Ventricular System of the Brain
- The ventricular system comprises the two lateral ventricles, the third ventricle and the fourth ventricle, all filled with cerebrospinal fluid.
- Each lateral ventricle lies within a cerebral hemisphere and has a body, an anterior horn, a posterior horn and an inferior horn.
- The lateral ventricle communicates with the third ventricle through the interventricular foramen of Monro.
- The third ventricle is a midline slit between the two thalami, connected across the midline by the interthalamic adhesion.
- The third ventricle communicates with the fourth ventricle through the cerebral aqueduct of the midbrain.
- The fourth ventricle is a diamond-shaped cavity behind the pons and upper medulla, roofed by the superior and inferior medullary vela.
- The floor of the fourth ventricle is the rhomboid fossa, formed by the dorsal pons and medulla.
- The fourth ventricle opens into the subarachnoid space through the median aperture of Magendie and the two lateral apertures of Luschka.
- The choroid plexus in the ventricles secretes cerebrospinal fluid and is a fold of pia and ependyma with a rich capillary bed.
- Cerebrospinal fluid flows from the lateral ventricles forward to the third, then the aqueduct, then the fourth, then out to the subarachnoid space.
- Obstruction anywhere along this path causes non-communicating hydrocephalus, with dilated ventricles upstream of the block.
- Aqueduct stenosis is a common cause of congenital non-communicating hydrocephalus.
- In an infant the open cranial sutures allow the head to enlarge when cerebrospinal fluid accumulates.
- The lateral apertures of Luschka lie at the lateral recesses of the fourth ventricle near the cerebellopontine angle.
- The septum pellucidum forms the medial wall of the anterior horns of the lateral ventricles.
Ventricular communications
- **Lateral to third ventricle:** Interventricular foramen of Monro, one on each side.
- **Third to fourth ventricle:** Cerebral aqueduct of the midbrain. Its stenosis causes congenital hydrocephalus.
- **Fourth ventricle to subarachnoid space:** Median aperture of Magendie and two lateral apertures of Luschka.
- **Choroid plexus:** Present in all ventricles; secretes cerebrospinal fluid; a fold of pia and ependyma with capillaries.
NMC competencies in this chapter
- **AN63.1:** Parts, boundaries and features of the third, fourth and lateral ventricles
- **AN63.2:** Anatomical basis of congenital hydrocephalus
Frequently Asked Questions
What are the openings of the fourth ventricle?
There are three: the single median aperture of Magendie and the two lateral apertures of Luschka. They allow cerebrospinal fluid to pass from the ventricular system into the subarachnoid space.
How does the lateral ventricle connect to the rest of the system?
Through the interventricular foramen of Monro, which opens into the third ventricle. From there the aqueduct leads to the fourth ventricle.
What causes non-communicating hydrocephalus?
A block within the ventricular pathway, most often aqueduct stenosis, so cerebrospinal fluid accumulates and dilates the ventricles upstream of the obstruction.
Where is cerebrospinal fluid produced?
By the choroid plexuses, folds of pia and ependyma with a rich capillary network, found in the lateral, third and fourth ventricles.
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