Normal pressure hydrocephalus (NPH) is a rise in cerebrospinal fluid (CSF) in the brain that affects brain function.

Normal pressure hydrocephalus (NPH) is a form of hydrocephalus, also known as "water on the brain," which means there is too much fluid pressing on the brain.

NPH can occur without a known cause, or it may be caused by any condition that blocks the flow of cerebrospinal fluid (CSF). The fluid-filled chambers (ventricles) of the brain enlarge to fit the increased volume of CSF. They press down on and damage or destroy brain tissue.

Risk factors include:

• Bleeding from a blood vessel or aneurysm in the brain (subarachnoid hemorrhage)
• Closed head injury
• Meningitis or similar infections
• Surgery on the brain (craniotomy)

The CSF is produced in normal amounts in these conditions, but it is prevented from being reabsorbed normally.

NPH is thought to account for about 5% of all dementias.

The symptoms often begin slowly.

Early symptoms include:

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

Symptoms as the disorder gets worse:

• Apathy
• Dementia
• Difficulty paying attention
• Impaired memory
• Less spontaneous behavior
• No mood (flat affect)
• Speech impairment
• Urinary or bowel incontinence
• Withdrawn behavior

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

Tests include:

• Lumbar puncture (spinal tap)
• Head CT scan or MRI of the head
• RHISA scan