In the Neuro Intensive Care Unit setting, the most frequent reasons for placing a ventriculostomy are bleeding into or around the brain and swelling of the brain. Bleeding into any one of the ventricles can cause blood cells to settle into the narrow connecting passages and clog them. Large deposits of blood in the subarachnoid space might limit CSF flow and impair absorption. Also, swelling in the lower structures of the brain might squeeze shut the outflow passages, trapping the CSF.
There can be other therapeutic reasons for ventriculostomy placement. Sometimes CSF pressure within the skull needs to be reduced to allow a CSF leak to heal. Or when intracranial pressures (ICP's) are high for reasons other than hydrocephalus (for example, bleeding or swelling within brain tissue itself), removing CSF can still help reduce ICP's. Also, by measuring ICP's, a ventriculostomy can guide ICP- reducing drug therapy.