Hydrocephalus - idiopathic

Alternative names
Normal pressure hydrocephalus (NPH); Hydrocephalus - adult; Hydrocephalus - communicating, “water on the brain”


Normal pressure hydrocephalus (NPH) is a brain disorder caused by blockage of the flow of cerebrospinal fluid, with enlargement of the ventricles within the brain and compression of the brain tissue.

It may result in loss of any or all brain functions controlled by the area of the brain which is compressed.

Causes, incidence, and risk factors

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, 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 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 (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)

Symptoms of progression of the disorder:

  • 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  • Withdrawn behavior  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

Signs and tests
An examination shows gait 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.

The goal of treatment is to improve symptoms. The surgical creation of a shunt that routes the CSF around the obstruction and back into the circulation is the treatment of choice.

Symptomatic treatment may vary depending on the symptoms presented and the extent that symptoms are relieved by treatment.

Expectations (prognosis)
Prognosis is poor without medical intervention. Symptoms progress and the disorder results in death.

Surgical treatment improves symptoms in about 50% of cases, with the best prognosis (probable outcome) for those with minimal symptoms. Other persons may have varying degrees of disability prior to death.


  • Injury from falls  
  • Temporary or permanent loss of brain functions  
  • Dementia  
  • Shortened life span  
  • Side effects of medications  
  • Complications of surgery (infection, bleeding)

Calling your health care provider
Call your health care provider if symptoms indicate normal pressure hydrocephalus may be present.

Call your health care provider if the condition of a person with NPH deteriorates to the point where you are unable to care for the person yourself.

Go to the emergency room or call the local emergency number (such as 911) if a sudden change in mental status occurs, as this may indicate development of another disorder.

Treatment of disorders associated with NPH may prevent its development in some cases. In other cases it may not be preventable, but early treatment may prevent progression to severe symptoms.

Johns Hopkins patient information

Last revised: December 8, 2012
by Armen E. Martirosyan, M.D.

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