Normal Pressure Hydrocephalus

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Normal Pressure Hydrocephalus

What is it?

Hydrocephalus is a condition where an excess of cerebrospinal fluid (CSF) accumulates within the ventricles of the brain. It occurs either due to overproduction of CSF or due to an obstruction of the CSF drainage passage.

A special type of Hydrocephalus is known as normal pressure Hydrocephalus. In this case there is a subtle, often incomplete obstruction of CSF drainage which results in a gradual excess of CSF within the ventricles. The intracranial pressure remains constant since the fluid accumulates so slowly that the brain compensates for the pressure by dilating the ventricles.

What causes it?

The cause of normal pressure hydrocephalus often can not be established but is thought to occur commonly due to scarring at the base of the brain (asymptomatic fibrosing meningitis). It may also develop after a subarachnoid hemorrage, chronic meningitis, head injury, paget disease of the skull or mucopolysaccharidosis.

What are the signs and symptoms?

Normal pressure Hydrocephalus is characterized by three classic patient findings:

Abnormal gait (Ataxia) - Unsteadiness and poor balance.
Dementia - Impaired mental function
Urinary Incontinence - Usually develops later in the disease process.

Patients with long standing normal pressure Hydrocephalus rarely complain of headaches and there is no papilledema.

The indolent nature of this syndrome often makes diagnosis difficult and the symptoms are often confused with other diseases such as Alzheimer's disease.

What tests may be done?

CT scan shows dilation of ventricular system with little atrophy of the brain cortex.
CSF flow study may be done in the Nuclear medicine department over a 2-3 day period. the dye is retained in the ventricles longer than in normal subject.
ICP monitoring often shows abnormal wave patterns.

How can it be treated?

Treatment of NPH often involves the placement of a ventriculoperitoneal shunt which drains the excess CSF from the ventricles into the abdominal cavity. This often results in substantial improvement of the patient's mental function and gait.

The opening pressure of the valve has to be chosen carefully as some patients may develop subdural haematoma if the ventricles are drained to rapidly.



CT of brain showing large lateral and 3rd ventricles in a patient with NPH.

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Last Updated: August 7, 2000
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