AQP4 and neuromyelitis optica: The disruption of the blood–CSF barrier in the choroid plexus was suspected to provide a route for AQP4-IgG to enter the CNS (173), and this may offer another possible explanation for the aforementioned specific distribution in the brain—the areas may be more accessible to the penetration of AQP4-IgG from the CSF and resemble ventriculitis and leptomeningitis in patients with NMO.