Obstruction to Flow of Cerebrospinal Fluid Can Cause Hydrocephalus
“Hydrocephalus” means excess water in the cranial vault. This condition is frequently divided into commu-nicating hydrocephalusand noncommunicating hydro-cephalus. In communicating hydrocephalus fluid flowsreadily from the ventricular system into the subarach-noid space, whereas in noncommunicating hydro-cephalus fluid flow out of one or more of the ventricles is blocked.
Usually the noncommunicating type of hydro-cephalus is caused by a block in the aqueduct of Sylvius, resulting from atresia (closure) before birth in many babies or from blockage by a brain tumor at any age. As fluid is formed by the choroid plexuses in the two lateral and the third ventricles, the volumes of these three ventricles increase greatly. This flattens the brain into a thin shell against the skull. In neonates, the increased pressure also causes the whole head to swell because the skull bones have not yet fused.
The communicating type of hydrocephalus is usually caused by blockage of fluid flow in the subarachnoid spaces around the basal regions of the brain or by block-age of the arachnoidal villi where the fluid is normally absorbed into the venous sinuses. Fluid therefore col-lects both on the outside of the brain and to a lesser extent inside the ventricles. This will also cause the head to swell tremendously if it occurs in infancy when the skull is still pliable and can be stretched, and it can damage the brain at any age. A therapy for many types of hydrocephalus is surgical placement of a silicone tube shunt all the way from one of the brain ventricles to the peritoneal cavity where the excess fluid can be absorbed into the blood.
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