Obstruction in the CSF pathways can occur at other levels. The lateral ventricles can become isolated when the pathways into the third ventricle (the foramen of Monroe) become obstructed. Obstruction can occur within the outlets of the fourth ventricle with dilation of all four ventricles resulting. One example of this would be hydrocephalus associated with a Chiari malformation.
With the introduction of endoscopic management of hydrocephalus, there has been a broadening of the definition of obstructive hydrocephalus. Increasingly it is thought to be represented by any obstruction of the CSF pathways below the level of the suprasellar cisterns, the fluid spaces outside the brain directly underneath the floor of the third ventricle. Consequently, many would include obstruction in the pathways around the outside of the brain stem in the definition of obstructive hydrocephalus.
The management of obstructive hydrocephalus has undergone a major shift during the past two decades. Most physicians experienced with endoscopy would seriously consider managing this form of hydrocephalus with a third ventriculostomy. For many, a third ventriculostomy is the treatment of choice for obstructive hydrocephalus. This is because of a lower long-term complication rate. It is import to realize that this procedure does not cure the hydrocephalus. Rather, it is simply a treatment, just as a shunt is a treatment and not a cure.