Endoscopic third ventriculostomy (ETV) is a surgical procedure in which an opening is created in the floor of the third ventricle

Third ventricle

The third ventricle is one of four connected fluid-filled cavities comprising the ventricular system within the human brain. It is a median cleft between the two thalami, and is filled with cerebrospinal fluid ....

 using an endoscope placed within the ventricular system through a burr hole. This allows the cerebrospinal fluid

Cerebrospinal fluid

Cerebrospinal fluid , Liquor cerebrospinalis, is a clear, colorless, bodily fluid, that occupies the subarachnoid space and the ventricular system around and inside the brain and spinal cord...

 to flow directly to the basal cisterns, thereby shortcutting any obstruction. It is used to treat certain forms of obstructive hydrocephalus, such as aqueductal

Cerebral aqueduct

The mesencephalic duct, also known as the aqueductus mesencephali, aqueduct of Sylvius or the cerebral aqueduct, contains cerebrospinal fluid , is within the mesencephalon and connects the third ventricle in the diencephalon to the fourth ventricle in the mesencephalon, which is between the pons...

 stenosis. Complications include subarachnoid hemorrhage

Subarachnoid hemorrhage

A subarachnoid hemorrhage , or subarachnoid haemorrhage in British English, is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain...

, basilar artery

Basilar artery

In human anatomy, the basilar artery is one of the arteries that supplies the brain with oxygen-rich blood.The two vertebral arteries and the basilar artery are sometimes together called the vertebrobasilar system, which supplies blood to the posterior part of circle of Willis and anastomoses with...

injury and hypothalamic or pituitary injury.