The Third Ventriculostomy

Inside your brain, there are 4 ventricles.  They consist of two lateral ventricles, the third ventricle, and the fourth ventricle.  The ventricles are filled with cerebrospinal fluid (CSF), which bathes and cushions and helps to protect the brain inside the skull.

The two lateral ventricles are relatively large and C-shaped.  There is one in each hemisphere of the brain.  They are connected to the third ventricle by the foramina of Monro.  The third ventricle is in the midline of the brain and is connected to the fourth ventricle by the aqueduct of Sylvius.  The aqueduct of Sylvius is very small and can be easily blocked, and thus is one of the primary causes of hydrocephalus.  In fact it is the location of the blockage that caused Nathan's hydrocephalus.

The fourth ventricle is also continuous with the central canal of the upper end of the spinal cord.  It provides CSF to the spinal column to help bathe and cushion the inside surface of the spinal cord.  The CSF in the spinal cord goes all the way down to the lumbar cistern near the bottom of the spinal cord.

A third ventriculostomy, sometimes referred to as an endoscopic third ventriculostomy (or ETV), is a surgical procedure that creates a bypass for the CSF around the blockage in the aqueduct of Sylvius and thus eliminates the need for a shunt.

Endoscopic means that the surgery is performed with the use of an endoscope, a thin tube that has a strong light, a powerful magnifying lens, and a passage through which tiny instruments can be passed.  Third ventriculostomy refers to the area where the bypass is made, in other words, through the thin membrane in the bottom of the third ventricle.

The CSF may then flow through the new opening to the normal fluid chambers below the base of the brain.  From there it can then be absorbed into the bloodstream like normal.