The University of Washington states that cerebrospinal fluid, the fluid in the brain and spinal cord, has four major functions: transporting hormones, protecting the brain, removing waste and creating buoyancy. When too much cerebrospinal fluid builds up in the brain, either due to an injury or illness, the extra fluid puts pressure on the brain. That excess pressure may cause damage to the brain.
Congenital Hydrocephalus
The National Institute of Neurological Disorders and Stroke or NINDS states that hydrocephalus, sometimes called "water on the brain," affects one in 500 children. While injuries or disease can cause hydrocephalus at any age, some people are born with hydrocephalus, called congenital hydrocephalus. For example, a patient with congenital hydrocephalus may have a genetic defect that causes aqueductal stenosis, which blocks the flow of cerebrospinal fluid, resulting in hydrocephalus. With hydrocephalus, the extra fluid in the brain widens the ventricles, which are the spaces in the brain. By enlarging the ventricles, the cerebrospinal fluid puts pressure on the brain tissue. Hydrocephalus also causes an increased head size.
Brain Tumors
Whether benign or malignant, a brain tumor puts extra pressure on the brain. A brain tumor can also increase the amount of fluid in the brain. The Children's Hospital of Wisconsin notes that increase intracranial pressure, a common symptom of a brain tumor, results from a blockage of one or more ventricles. Without being able to pass through the ventricles, extra fluid accumulates in the brain. As a result, patients have headaches, nausea, vomiting in the morning, drowsiness and irritability.
Brain Aneurysm
A widening of a blood vessel, a brain aneurysm causes problems for a person when it ruptures. The Mayo Clinic notes that when the aneurysm ruptures, it bleeds between the brain and surrounding tissue, a condition called a subarachnoid hemorrhage. When the subarachnoid hemorrhage occurs, the blood blocks the movement of the cerebrospinal fluid, causing a buildup of the fluid in the brain.
Other Causes
Damage to the brain, such as from a traumatic brain injury, can cause a build up of cerebrospinal fluid in the brain. A ruptured blood vessel or a blocked vessel, which causes a stroke, can lead to extra fluid in the brain. Another bleeding cause of extra fluid in the brain is intraventricular hemorrhage, a complication of a premature birth. With intraventricular hemorrhage, the bleeding occurs in the ventricles. The NINDS notes that neural tube defects, such as encephalocele and spinal bifida, can cause cerebrospinal fluid build up. If the neural tube, which develops into the spinal cord and surrounding tissues, does not fully form, the cerebrospinal fluid does not circulate properly. Meningitis, which results in the inflammation of the membranes around the brain and spinal cord, also causes extra fluid in the brain.
