Limited areas of the brain that lack a blood-brain barrier and are adjacent to the ventricular system of the brain.
The following areas are counted as circumventricular organs:
1/ Eminentia mediana
2/ Subfornical organ
3/ Organum vasculosum in lamina terminalis
4/ Posterior lobe of the pituitary gland
5/ Subcommissural organ
6/ Pineal gland
7/ Area postrema