CT Brain Anatomy
CSF spaces

Key points

  • The CSF spaces comprise the sulci, fissures, basal cisterns and ventricles
  • An appreciation of the normal appearances of the CSF spaces is required to allow assessment of brain volume

The brain is surrounded by cerebrospinal fluid (CSF) within the sulci, fissures and basal cisterns. CSF is also found centrally within the ventricles. The sulci, fissures, basal cisterns and ventricles together form the 'CSF spaces', also known as the 'extra-axial spaces'.

CSF is of lower density than the grey or white matter of the brain, and therefore appears darker on CT images.

An appreciation of the normal appearances of the CSF spaces is required to allow assessment of brain volume.

Sulci

The brain surface is formed by folds of the cerebral cortex known as gyri. Between these gyri there are furrows, known as sulci, which contain CSF.

Sulci and gyri - CT brain

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Sulci and gyri

  • Gyrus = a fold of the brain surface (plural = gyri)
  • Sulcus = furrow between the gyri which contains CSF (plural = sulci)

Fissures

The fissures are large CSF-filled clefts which separate structures of the brain.

Fissures - CT brain

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Fissures

  • The interhemispheric fissure separates the cerebral hemispheres - the two halves of the brain
  • The Sylvian fissures separate the frontal and temporal lobes

Ventricles

The ventricles are spaces located deep inside the brain which contain CSF.

Lateral ventricles - CT brain

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Lateral ventricles

  • The paired lateral ventricles are located on either side of the brain
  • The lateral ventricles contain the choroid plexus which produces CSF
  • Note : The choroid plexus is almost always calcified in adults

Third ventricle - CT brain

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Third ventricle

  • The third ventricle is located centrally
  • The lateral ventricles communicate with the third ventricle via small holes (foramina of Monro).

Fourth ventricle - CT brain

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Fourth ventricle

  • The fourth ventricle is located in the posterior fossa between the brain stem and cerebellum
  • It communicates with the third ventricle above via a very narrow canal, the aqueduct of Sylvius (not shown)

Basal cisterns

  • CSF in the basal cisterns surrounds the brain stem structures