blood brain barrier

The blood-brain barrier (BBB) forms a physical resistance to the passage of lipophobic substances from cerebral capillaries into the brain and is a key reason why there is no CSF enhancement following intravenous contrast media on CT and MRI.

Gross anatomy

The blood-brain barrier is formed by a combination of endothelial cells, pericytes, and astroglial and perivascular macrophages along the cerebral capillary walls.

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

• continuous: present in areas which have a blood-brain barrier
  • continuous interendothelial tight junctions
  • no pinocytosis
  • no fenestrations
• fenestrated: present in areas which lack the blood-brain barrier
• sinusoidal: not found in the brain

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

Areas which contain fenestrated capillaries, and thus lack the blood-brain barrier, are:

•  circumventricular organs (CVO)
  • area postrema
  • median eminence
  • subforniceal region
  • posterior pituitary gland
  • pineal gland
  • organum vasculosum
  • lamina terminalis
• choroid plexus
• dura mater

Generally, lipophilic solutes can cross the blood-brain barrier, including:

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

Hydrophilic solutes, in general, are unable to cross it, e.g. water soluble CT/MRI contrast media.

Related pathology

There are a multitude of conditions associated with disruption of the blood-brain barrier:

• temporal lobe epilepsy (TLE)
• posterior reversible encephalopathy syndrome (PRES)
• hypoxia, ischemia and infarction
• tumors
• inflammatory conditions, e.g. meningitis
• trauma
• intracranial irradiation
• multiple sclerosis
• progressive multifocal leukoencephalopathy: the JC virus can cross the blood-brain barrier

See also

• blood-ocular barrier

Siehe auch:

• Encephalomyelitis disseminata
• Meningitis
• Glandula pinealis
• Progressive multifokale Leukenzephalopathie
• posteriores reversibles Enzephalopathiesyndrom
• Temporallappenepilepsie
• Schrankenstörung nach Infarkt
• Schrankenstörung

und weiter:

• Hirnödem
• Hypophysenstiel