After addition of more CSF from the fourth ventricle, it escapes into the subarachnoid space through the foramina of Magendie and Luschka. The CSF then circulates throughout the base of the brain, down around the spinal cord as well as upward over the cerebral hemispheres. It is defined as a disproportionate enlargement of part or all of the ventricular system due to an excess of CSF and is typically accompanied by serious increase in intracranial pressure. Increased ICP can occur as a result of an increased mass within the limited volume of the cranium. Examples include an increase in CSF volume, cerebral edema, and growing mass lesions such as tumors and hematomas.
Cerebral edema is the increase in brain tissue water causing swelling.
It may occur secondary to head injury, infarction or a response to adjacent hematoma or tumor. Uncorrected increased ICP can lead to further brain damage due to the pressure and inadequate blood perfusion of neurological tissues. Williams and Wilkins. Clemente, Camine D. Anatomy. A Regional Atlas of the Human Body .