Acute CT Brain
Brain volume

Key points

  • Assess brain volume by assessing volume of the CSF spaces
  • Age must be taken into account when assessing brain volume

Brain volume is assessed by subjectively estimating relative volume of the cerebrospinal fluid spaces (CSF spaces). However, the age of the patient must be taken into account. The ventricles may be very small in young adults and very large in the elderly and still be considered normal.

Brain volume decreases throughout adulthood and with certain disease processes such as dementia or alcoholism.

There are no agreed measurements to quantify brain volume. An estimation of brain volume can be made by subjective assessment of volume of the CSF spaces (sulci, fissures, ventricles and basal cisterns).

Brain volume - young v old

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Brain volume - young v old

  • Size of the CSF spaces varies with age

Normal v abnormal brain volume

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Normal v abnormal brain volume

  • Assessment of the size of the sulci is often easiest near the vertex of the brain
  • Both these patients are in their 60s
  • The image on the right shows loss of volume with corresponding enlargement of the sulci in an alcoholic individual

Hydrocephalus

Hydrocephalus is the result of increased production or decreased absorption of cerebrospinal fluid (CSF). Hydrocephalus can result in massive enlargement of the ventricles. Acute hydrocephalus may cause damage to the ependyma (the lining of the ventricles) which results in oedema of the periventricular white matter. This is known as transependymal oedema.

Hydrocephalus - CT brain

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Hydrocephalus

  • The ventricles are massively enlarged
  • The periventricular white matter appears of low density due to transependymal oedema
  • The sulci are not enlarged

Alzheimer's disease

Although Alzheimer's disease, the commonest cause of dementia, cannot be diagnosed on the basis of imaging findings alone, there are certain features which are characteristic. The typical pattern in Alzheimer's is of volume loss predominantly affecting the medial side of the temporal lobes.

Alzheimer's disease - CT brain

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Alzheimer's disease

  • The temporal lobes are much reduced in volume - particularly on their medial side
  • Enlargement of the temporal horns of the lateral ventricles - as shown in this image - is a specific sign of volume loss of the temporal lobes

Increased brain volume - cerebral oedema

Generalised cerebral oedema can cause the brain to swell so that there is generalised reduction of the CSF space volume and loss of differentiation between the grey and white matter.

Hypoxic brain injury with cerebral oedema

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Hypoxic brain injury with cerebral oedema

  • The image shows striking loss of differentiation between grey and white matter structures due to generalised cerebral oedema
  • The ventricles and sulci are very small for a patient of this age indicating generalised brain swelling
  • This 75 year old patient had a prolonged period of hypoxia during cardiopulmonary resuscitation