Ventriculostomy is also called ventricular catherization with an intraventricular catheter (IVC) or external ventricular drainage (EVD).  It is a surgical procedure that involves the placement of a catheter connecting the ventricles of the brain to an external collecting device.  The ventricles are the four spaces inside the brain that contain cerebrospinal fluid (CSF), which is necessary for supporting and nourishing the brain. The fluid circulates through the ventricles and around the spinal cord under normal circumstances.  This normal circulation may become blocked, causing hydrocephalus (excess CSF), which can cause brain compression due to the limited space inside the cranial cavity.  In order to remove excess CSF, a catheter will be placed inside one ventricle leading to a collection device located outside the cranial cavity. Ventriculostomy may be performed in cases where there is bleeding into the ventricles, which may also block the circulation of the cerebrospinal fluid, or when the pressure inside the skull (intracranial pressure) is elevated after traumatic brain injury. As part of the operation the surgeon will shave the side of the head on which the catheter will be inserted, usually the right side, and insert the catheter perpendicular to the brain surface, about 5-7 centimeters deep.  The placement of the catheter may be temporary if the cause can be resolved.  In cases where external drainage is permanently necessary, a ventriculostomy may be converted to a ventriculo-peritoneal shunt or other internalized shunt.  The risks of the procedure are small, but include infection of the cerebrospinal fluid and brain hemorrhage.