GNP 5

Q.  Describe the flow of CSF from origination to absorption.

A.  CSF is formed from capillaries in the CNS and leptomeninges, primarily from the highly vascular choroid plexus in the ventricles.  35% comes from 3^rd and lateral ventricles, 23% from the 4^th ventricle, and 42% from the subarachnoid space.  CSF will have less potassium, calcium, glucose, and dramatically less protein.  It will have more chloride, sodium, and magnesium compared to blood.  CSF is produced at about 0.045ml/min in dogs and at about 1/3 of that (0.15ml/min) in cats and will generally turn over 3-5 times/ day.  CSF flows (due to arterial pulsations and ciliary movement) from the lateral ventricles to the 3^rd ventricle via the interventricular foramen.  It then flows to the 4^th ventricle and then into the subarachnoid space via the lateral apertures.  The fluid will flow either caudally over the spinal cord or will go rostrally to flow over the cerebellum, under the tentorium, and over the cerebrum to be absorbed by the venous sinuses. 

Veterinary Neuroanatomy and Clinical Neurology, 3^rd edition.  De Lahunta, Glass.  Saunders Elsevier 2009: pp 54-56.