Normal pressure hydrocephalus (NPH) is a brain disorder that occurs when the flow of cerebrospinal fluid (CSF) is blocked. The fluid fills up in the brain and pushes on brain tissue. The person may lose any or all brain functions controlled by the area of the brain affected.

Normal pressure hydrocephalus (NPH) can be a reversible or treatable disorder. It is thought to account for about 5% of all dementias. The symptoms often begin gradually.

NPH is a form of hydrocephalus, also known as "water on the brain", which means there is too much fluid compressing the brain. It can occur without identifiable cause, or it may be caused by any condition where the flow of cerebrospinal fluid (CSF) is blocked. The CSF is produced in normal amounts in this condition, but it is prevented from being normally re-absorbed.

The ventricles (fluid-filled chambers) 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 closed head injury, surgery on the brain (craniotomy), meningitis or similar infections, and subarachnoid hemorrhage (bleeding from a blood vessel or aneurysm in the brain).

Early symptoms include:

• Changes in gait, including inability to begin walking (gait apraxia)
• Unsteady walking
• Weakness of the legs
• Sudden fall without loss of consciousness or other symptoms (drop attacks)

• Dementia (loss of any or all brain functions, including movement, sensation, perception, and thought processes) -- originally mild, may progress to severe dementia
• No observable mood (flat affect)
• Apathy
• Withdrawn behavior
• Impaired memory
• Difficulty maintaining attention
• Decreased spontaneity
• Urinary or bowel incontinence (loss of control over function)
• Speech impairment

An examination shows gait (walking) changes related to the damage within the brain. Deep tendon reflexes may be increased in the lower legs.

• A lumbar puncture (spinal tap) may show normal pressure of CSF in the spine.
• A head CT scan or MRI of head may show changes that indicate NPH.
• A RHISA scan (a nuclear scan using radioactivity) may show changes of the circulation within the brain, or reflux of CSF into the ventricles.