Revision 18 for 'Blood brain barrier'

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Blood brain barrier

The blood brain barrier (BBB) forms a physical resistance to the passage of lipophobic substances form cerebral capillaries into the brain and is a key reason why there is no CSF enhancement following IV contrast media in CT and MR imaging.

It is formed by a combination of endothelial cells, pericytes, and astroglial andperivascular macrophages along the cerebral capillary walls.

In general, capillary walls in the human body can comprise of three different types

  • continuous : present in areas which have a BBB
    • continuous inter endothelial tight junctions
    • no pinocytosis
    • no fenestrations
  • fenestrated : present in areas which lack the BBB
  • sinusoidal : not found in the brain

In the brain, the majority of capillary walls are of the continuous type with tight junctions and a continous basement membrane

Areas which have fenestrated capillaries and thus lack the blood brain barrier are termed circumventricular organs (CVO) and include

Generally lipophilic solutes can cross the BBB which include

  • caffeine
  • ethanol
  • radiopharmaceuticals used in PET and SPECT imaging
  • CO2
  • O2
  • nicotine

Hydrophilic solutes in general on the other hand are unable to cross it

  • e.g. water soluble CT / MR contrast media

There are a multitude of conditions that are associated with disruption of the BBB. They include

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