In non communicating hydrocephalus there exists an obstruction to the passage of CSF from the ventricular system into the subarachnoid space. The classic example is aqueductal stenosis, in which there is enlargement of the lateral and third ventricles without enlargement of the fourth ventricle. If an opening can be created in the third ventricle proximal to the site of obstruction, then CSF can escape into the subarachnoid space and bypass the obstruction. If there is no coexisting blockage in the subarachnoid space, CSF can be absorbed into the venous system and hydrocephalus can be brought under control without using an extracranial shunt.

Endoscopic Third Ventriculostomy ( ETV ) fenestrating the floor of the 3rd ventricle was done today for an Iraqi child in the Neurosurgical Hospital in Baghdad.