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) ¹

• 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