CSF is produced in the brain by modified ependymal cells in the choroid plexus (approx. 50-70%), and the remainder is formed around blood vessels and along ventricular walls. It circulates from the lateral ventricles to the foramen of Monro (Interventricular foramen), third ventricle, aqueduct of Sylvius (Cerebral aqueduct), fourth ventricle, foramina of Magendie (Median aperture) and foramina of Luschka (Lateral apertures); subarachnoid space over brain and spinal cord; reabsorption into venous sinus blood via arachnoid granulations.
It had been thought that CSF returns to the vascular system by entering the dural venous sinuses via the arachnoid granulations (or villi). However, some[1] have suggested that CSF flow along the cranial nerves and spinal nerve roots allow it into the lymphatic channels; this flow may play a substantial role in CSF reabsorbtion, in particular in the neonate, in which arachnoid granulations are sparsely distributed. The flow of CSF to the nasal submucosal lymphatic channels through the cribriform plate seems to be specially important.
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