Ventricular System

The ventricular system is an extension of the subarachnoid space into the brain consisting of a series of interconnecting spaces and channels. Four chambers are filled with cerebrospinal fluid (CSF): the paired lateral ventricles, the unpaired 3rd ventricle, and the unpaired 4th ventricle. Connections between the structures occur via the interventricular foramen of Monro and the cerebral aqueduct (sylvian aqueduct). The foramen of Magendie and the foramen of Luschka, are additional channels present in the 4th ventricle.

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Topography and Relations of the Ventricular System

The ventricular system consists of 4 ventricles with an aqueduct connecting the 3rd and 4th ventricles. Cerebrospinal fluid (CSF) flows through the ventricles before entering the subarachnoid space of the brain and spinal cord from the 4th ventricle:

  • Lateral ventricles:
    • Body:
      • Contained in the frontal and parietal lobes 
      • Extends from the interventricular foramen of Monro to the splenium of the corpus callosum
    • Anterior horn: in the frontal lobe
    • Posterior horn: curves posteromedially into the occipital lobe
    • Inferior horn:
      • Largest compartment of the lateral ventricle
      • Extends forward into the temporal lobe
  • 3rd ventricle:
    • A midline, slit-like cavity
    • Derived from the primitive forebrain vesicle
  • Cerebral aqueduct (of Sylvius): 
    • Small tube extending throughout the dorsal quarter of the midbrain
    • Surrounded by periaqueductal gray
    • Connects the 3rd and 4th ventricles
  • 4th ventricle: 
    • Between the brainstem and the cerebellum
    • The foramen of Luschka (lateral aperture) and the foramen of Magendie (median aperture) allow newly produced CSF to enter the subarachnoid space.
  • Circumventricular organs:
    • Structures characterized by extensive, highly permeable capillaries
    • Surround the 3rd and 4th ventricles
    • Regions do not typically contain a blood-brain barrier, which allows for communication between the peripheral blood and the CSF.
Ventricles of the brain

Ventricles of the brain

Image: “Ventricles of the brain” by Bruce Blaus. License: CC BY 3.0, edited by Lecturio.

Choroid Plexus and Cerebrospinal Fluid

Choroid plexus

  • Vascular pia mater in all ventricles
  • Location:
    • Roof of the temporal horns of the lateral ventricles
    • Floor of the body of the lateral ventricles
    • Foramen of Monro
    • Roof of the 3rd ventricle
    • Medullary of the 4th ventricle, extending through the foramen of Luschka
  • Actively secretes CSF in the lateral, 3rd, and 4th ventricles
Choroid plexus development

Choroid plexus development: The choroid plexus is located throughout the ventricular system and is responsible for the secretion of cerebrospinal fluid.

Image by Lecturio.

Cerebrospinal Fluid

  • Clear, colorless liquid containing a small amount of protein
  • Provides buoyancy and protection for the brain
  • Regulates chemical concentration of neurotransmitters and metabolic waste

Subarachnoid Space and Circulation of Cerebrospinal Fluid

Subarachnoid space

  • Between the arachnoid and the pia mater
  • Contains CSF, larger arteries and veins, and intracranial and intervertebral portions of the cranial and spinal nerves

Circulation of cerebrospinal fluid

  • After production in the ventricles, CSF flows into the subarachnoid space.
  • CSF flows freely within the subarachnoid space of the brain and spinal cord.
  • CSF is reabsorbed by arachnoid granulations into the venous circulation.
Circulation

Circulation of the cerebrospinal fluid (CSF):
Note the emergence of CSF from the choroid plexus into the ventricles. Cerebrospinal fluid is reabsorbed by arachnoid granulations into the venous circulation.

Image: “Circulation” by OpenStax. License: CC BY 4.0, edited by Lecturio.

Clinical Relevance

  • Hydrocephalus: a potentially life-threatening condition caused by the excess accumulation of CSF within the ventricular system. The clinical presentation is nonspecific and may include headache, behavioral changes, developmental delays, or nausea and vomiting. Diagnosis is confirmed with neuroimaging (ultrasound, head CT, or MRI) showing ventriculomegaly. Treatment is placement of a CSF shunt.
  • Normal pressure hydrocephalus (NPH): enlargement of the ventricles without detectable elevations in intracranial pressure. Normal pressure hydrocephalus occurs most commonly in adults > 60 years of age. Symptoms include a triad of urinary incontinence, ataxia, and cognitive dysfunction and may be remembered by the mnemonic “wet, wobbly, and wacky.”
  • Chronic microvascular ischemic disease: chronic atherosclerotic disease typically resulting in hypoperfusion to symmetric areas of the cerebral cortex and causing cerebral atrophy or other brain malformations. Unlike hydrocephalus, the intracranial pressure is not elevated. 
  • Chiari malformations (CM): a group of disorders defined by structural deficits in the brain and spinal cord leading to limited space in the posterior fossa and forcing cerebellar structures to protrude through the foramen magnum. Type II Chiari malformations are seen in combination with herniation of the cerebellar vermis, the brainstem, and the 4th ventricle into the foramen magnum. An association exists with myelomeningocele and multiple brain anomalies, including hydrocephalus and syringomyelia.

References

  1. Kahle, K. T., Kulkarni, A. V., Limbrick, D. D., & Warf, B. C. (2016). Hydrocephalus in children. Lancet, The, 387(10020), 788–799. http://dx.doi.org/10.1016/S0140-6736(15)60694-8
  2. Blázquez, M., & Zarranz, J. J. (2018). Síndrome meníngeo. edema cerebral. hipertensión intracraneal. hidrocefalias. hipotensión intracraneal. In J. J. Zarranz (Ed.), Neurología (pp. 219-233). https://www.clinicalkey.es/#!/content/3-s2.0-B978849113071000012X
  3. Sato, O., Yamguchi, T., Kittaka, M., & Toyama, H. (2001). Hydrocephalus and epilepsy. Child’s nervous system: ChNS: official journal of the International Society for Pediatric Neurosurgery, 17(1-2), 76–86.
  4. Tubbs, R. S., & Oakes, W. J. (2017). Chiari malformations. Neurological surgery. pp. 1531–1540. http://dx.doi.org/10.1016/B978-0-323-28782-1.00190-8
  5. Schijman, E. History, anatomic forms, and pathogenesis of Chiari I malformations. Childs Nerv Syst 20, 323–328 (2004). https://doi.org/10.1007/s00381-003-0878-y
  6. Khoury, C. (2020). Chiari malformations. UpToDate. Retrieved December 1, 2020 from https://www.uptodate.com/contents/chiari-malformations
  7. Abd-El-Barr M. M., Strong C.I., Groff M. W. Chiari malformations: diagnosis, treatments and failures. J Neurosurg Sci. 2014 Dec. 58 (4):215–21.
  8. McClugage, S and Oakes, J. The Chiari I malformation. JNSPG 75th Anniversary Invited Review Article. https://doi.org/10.3171/2019.5.PEDS18382

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