Circumventricular organs (CVO) are cerebral areas with incomplete endothelial blood-brain barrier (BBB) and therefore regarded as "gates to the brain". During inflammation, they may exert an active role in determining immune cell recruitment into the brain.
Wuerfel, E., Infante-Duarte, C., Glumm, R., & Wuerfel, J. T. (2010). Gadofluorine M-enhanced MRI shows involvement of circumventricular organs in neuroinflammation. Journal of Neuroinflammation, 7. https://doi.org/10.1186/1742-2094-7-70