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PH-NE10

Cerebral oedema

Why the brain swells in four ways (a leaking barrier, failing cell pumps, CSF pushed into the ventricle wall, plasma more dilute than brain), how each looks to the eye, the microscope and the scanner, and why the type decides which treatment works.

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  • 5 steps · 10 questions
  • 3D anatomy, affected parts marked

By the end, you can

  • Explain how the blood–brain barrier, astrocytes and the ependyma control water in the brain, and why plasma osmolality rather than albumin sets the balance.
  • Explain the mechanisms of vasogenic, cytotoxic, interstitial and osmotic oedema and name the main causes of each.
  • Relate each type to where the water collects and to its appearance to the eye, under the microscope and on CT and MRI, including diffusion imaging.
  • Explain how mixed and evolving oedema harms the brain locally and by raising intracranial pressure.
  • Recognise the classic appearances and tests of cerebral oedema, and explain why corticosteroids, osmotic agents, CSF drainage and slow correction each work only for certain types.

What it is

Cerebral oedema is an increase in the water content of brain tissue that enlarges its volume. It is classified by mechanism: vasogenic (plasma leaks through a damaged blood–brain barrier into the spaces between cells), cytotoxic (cells swell when their ion pumps fail, the barrier intact at first), interstitial (CSF is forced from the ventricles into the surrounding white matter in hydrocephalus) and osmotic (water is drawn into the brain when the plasma becomes more dilute than brain tissue). Most real injuries mix types, and the mix changes over days.

4 types to tell apart
Vasogenic
A leaking barrier around tumours, abscesses, inflammation and contusions; protein-rich fluid spreads between white-matter fibres.
Cytotoxic
Energy failure in ischaemia, cardiac arrest and severe injury stops the sodium–potassium pump, so astrocytes and neurones swell in grey and white matter alike.
Interstitial (hydrocephalic)
Raised pressure in blocked ventricles drives CSF across their lining into the periventricular white matter.
Osmotic
A fall in plasma osmolality (acute low sodium, or too-rapid lowering of a high sodium or glucose) draws water into the whole brain across an intact barrier.

US spelling: oedema → edema.

Normal function

How the brain controls its water

Brain capillaries are unlike those elsewhere. Their are sealed together by tight junctions, have no pores and carry few transport vesicles: the blood–brain barrier. Water crosses it easily, but sodium, chloride, plasma proteins and many drugs do not. Because sodium cannot leak through, the water balance of the brain follows the total concentration of the plasma (its osmolality, set mostly by sodium) rather than the albumin-driven forces that govern capillaries in other tissues.

The capillaries are wrapped in the end-feet of , whose membranes are packed with water channels (aquaporin-4). Astrocytes take up the potassium and glutamate released by active , and water follows, so they are the cells that swell first when the brain is injured. The spaces between cells are narrow, about a fifth of the tissue volume, and brain tissue has no lymphatic vessels: excess fluid drains slowly towards the ventricles and the cerebrospinal fluid (CSF).

The ventricles are lined by a single layer of ependymal cells, across which CSF and tissue fluid exchange. The two kinds of brain tissue resist fluid differently: grey matter is densely packed with cell bodies, dendrites and synapses, while white matter is made of parallel bundles of myelinated axons with looser spaces between them, along which fluid spreads more easily.

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