It is a term frequently and mistakenly interchanged with ventriculomegaly, that is, large cerebral ventricles. Ventriculomegaly on imaging studies does not necessarily indicate increased pressure. Hydrocephalus may be caused by either the over-production or the malabsorption of CSF, the latter being far more common. CSF is produced in the fluid filled cavities of the brain called ventricles. Two types of tissue line the ventricles, the ependyma and the choroid plexus.
Choroid plexus is regionally specialized ependyma that secrets a transudate of serum.
Hydrocephalus caused by the over-production of CSF from a tumor called a choroid plexus papilloma is rare. The vast majority of hydrocephalus is caused by CSF malabsorption. CSF produced by the choroid plexus of the lateral ventricle must travel through the foramen of Monro, the third ventricle, the aqueduct of Sylvius, the fourth ventricle and finally into the subarachnoid spaces. The subarachnoid spaces convey CSF over the surface of the brain to the arachnoid villi of the superior sagittal sinus. There, the CSF is absorbed into the venous blood stream.