Normal pressure hydrocephalus (NPH) can be a reversible or treatable disorder. It is thought to account for about 5% of all dementias. The incidence is 1 out of 100,000 people. NPH can occur at any age. The onset of symptoms is often gradual.
NPH is a form of hydrocephalus ("water on the brain", too much brain fluid). It can occur without identifiable cause, or it may be caused by any condition where there is an obstruction to the flow of cerebrospinal fluid (CSF). The CSF is produced in normal amounts in this condition, but it is prevented from being normally re-absorbed.
The ventricles of the brain enlarge to accommodate the increased volume of CSF so the pressure of CSF, when measured by lumbar puncture (spinal tap), remains normal. Brain tissue is damaged or destroyed because of compression by the fluid-filled ventricles. If there is an identifiable cause and the cause can be corrected, the symptoms may reverse or at least stop getting worse. If there is no identifiable cause, the disorder is often progressive.
Risk factors include disorders that may cause obstruction of the flow of CSF, such as head injury (closed), surgery on the brain (craniotomy), meningitis or similar infections, and subarachnoid hemorrhage (bleeding from a blood vessel or aneurysm in the brain).
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