WHAT IS NORMAL PRESSURE HYDROCEPHALUS?

Normal pressure hydrocephalus is a type of hydrocephalus characterized by increased cerebrospinal fluid and a widening of the ventricles of the brain, usually without causing increased pressure inside the head. The pressure is usually normal because the ventricles widen to make room for the extra fluid. A consequence of this widening, however, is that the increased fluid presses against certain brain structures, damaging or destroying them.

Although normal pressure hydrocephalus usually presents without an increase of pressure inside in the head, increased pressure can happen if the condition goes untreated. Increased pressure on brain structures can cause worsen the signs described below and cause significant brain damage.

WHAT CAUSES NORMAL PRESSURE HYDROCEPHALUS?

Many times, the cause of normal pressure hydrocephalus is unknown. However, the condition is often caused by a failure of the arachnoid granulations (see earlier section) to absorb enough of the cerebrospinal fluid. As a result, the cerebrospinal fluid level increases, even though it is being produced in normal amounts.

In other cases, something is blocking the flow of cerebrospinal fluid, causing normal pressure hydrocephalus. Any condition that causes a blockage of cerebrospinal fluid can lead to normal pressure hydrocephalus. Some causes of blocked cerebrospinal fluid include a closed head injury, brain surgery, brain tumors, and infections in the brain. Normal pressure hydrocephalus general occurs weeks after brain infections such as meningitis. Meningitis is an inflammation of the meninges (the three outer coverings of the brain and spinal cord). Meningitis can cause scarring to the arachnoid granulations, which help absorb cerebrospinal fluid. If the arachnoid granulations are scarred, they will not absorb the cerebrospinal fluid adequately.

A subarachnoid hemorrhage can also cause normal pressure hydrocephalus. A subarachnoid hemorrhage is when bleeding occurs in the space between two of the layers that cover the brain - the arachnoid mater and the pia mater. In the case of a subarachnoid hemorrhage, the blood is what blocks the flow of cerebrospinal fluid. Generally, this blockage occurs in the outlets of the fourth ventricle or in the cerebral aqueduct. The cerebral aqueduct is a narrow opening in the brain that connects the third ventricle with the fourth ventricle, allowing cerebrospinal fluid to flow between these two areas. It can be viewed in the picture above.

About 10-20% of patients with a subarachnoid hemorrhage will develop normal pressure hydrocephalus that causes noticeable signs. Normal pressure hydrocephalus may take up to several months to develop after a subarachnoid hemorrhage has occurred. Many head injuries cause subarachnoid hemorrhages.

Although very rare, it does appear that in some cases normal pressure hydrocephalus can be inherited (passed on through the genes of one's parents). This is still debatable, however. Genes are tiny structures that contain coded instructions for how proteins should be constructed and how certain bodily characteristics should develop. For example, genes control the natural color of people's eyes and hair, and whether they will be male or female. Genes are passed on from parents to their children.

WHAT ARE RISK FACTORS FOR NORMAL PRESSURE HYDROCEPHALUS?

Risk factors for normal pressure hydrocephalus include closed head injury, brain surgery, infections in the brain, and a subarachnoid hemorrhage (see earlier section). Other risk factors for normal pressure hydrocephalus include high blood pressure, coronary artery disease, and diabetes mellitus. Coronary artery disease is a narrowing of coronary arteries, which are blood vessels that supply the heart with blood.

Diabetes mellitus is a complex, long-term disorder in which the body is not able to effectively use a natural chemical called insulin. Insulin's main job is to quickly absorb glucose (a type of sugar) from the blood into cells for their energy needs and into the fat and liver (a large organ that performs many chemical tasks) cells for storage.

Another risk factor for normal pressure hydrocephalus is a low level of HDL in the blood. HDL stands for high-density lipoprotein cholesterol. Cholesterol is a waxy, fatty substance found only in animal tissues. HDL is called the "good cholesterol" because it helps prevent cholesterol from building up in your arteries.

HOW IS THE PRESSURE OF CEREBROSPINAL FLUID MEASURED?

The pressure of cerebrospinal fluid is most commonly measured with a spinal tap (also known as a lumbar puncture). A spinal tap is a procedure in which a needle is inserted into a space inside the spinal canal for the purpose of removing some of the cerebrospinal fluid. The spinal canal is the space between the spinal cord and the bony structure that surrounds it. It is because the pressure inside the head is usually normal, that this condition is called normal pressure hydrocephalus.

IS THE PRESSURE OF CEREBROSPINAL FLUID ALWAYS NORMAL IN NORMAL PRESSURE HYDROCEPHALUS?

Actually, the answer is no. The pressure of cerebrospinal fluid in normal pressure hydrocephalus can be higher than normal in some cases, particularly in the beginning stage. After the beginning stage, however, the pressure usually returns to normal as the ventricles enlarge to hold the increased fluid. In some cases, increased cerebrospinal fluid pressure can occur in the middle stage of this condition. Thus, the term normal pressure hydrocephalus is not entirely an accurate term in some cases.

WHAT ARE THE SIGNS OF NORMAL PRESSURE HYDROCEPHALUS?

There are three main signs of normal pressure hydrocephalus that usually occur gradually rather than suddenly. These signs are difficulty walking, difficulty holding in urine, and difficulty thinking. The difficulty walking usually presents as a slowed, shuffling walk, in which the feet appear stuck to the ground. The person may appear unsteady when walking, may have difficulty starting to walk, may have difficulty making turns, and may also complain of weakness in the legs.

The difficulty walking may lead to sudden falls without a loss of consciousness. Difficulty walking in normal pressure hydrocephalus seems to be associated with increased tension in the extensor muscles of the legs. The extensor muscles are muscles that extend (the opposite of flex) body parts). It should be noted that some patients with normal pressure hydrocephalus only present with a difficulty walking.

In addition to difficulty holding in urine, the person may also have difficulty holding in feces. This only occurs in rare circumstances, however. In earlier stages, patients may not lose control of their ability to hold in urine or feces, but they may have increased urges to urinate or have bowel movements, and may actually perform these bodily functions more often.

The thinking difficulties in normal pressure hydrocephalus are usually characterized by confusion, poor attention, slowed thinking, and memory difficulties. The thinking difficulties can eventually progress into a dementia. Dementia is a mental disorder characterized by a significant loss of intellectual and cognitive abilities without impairment of perception or consciousness. It is estimated that about 5% of all dementias are due to normal pressure hydrocephalus. If treated early enough, dementia from normal pressure hydrocephalus can be reversible. The dementia will initially present as mild and can progress to severe.

Patients with normal pressure hydrocephalus may have rigid muscles and tremors (uncontrollable shaking movements). Patients with normal pressure hydrocephalus may have an abnormally weak voice due to incoordination of the muscles that control speech.

A person with normal pressure hydrocephalus may have no observable mood. That is, they do not appear happy or sad, but rather indifferent and withdrawn. Their facial expressions may appear to be very restricted. They may not be very spontaneous in terms of movements or conversations, requiring other people to act first before they speak or move. Expressive speech may be impaired in people with normal pressure hydrocephalus.

WHAT CAUSES THE SIGNS OF NORMAL PRESSURE HYDROCEPHALUS?

The signs of normal pressure hydrocephalus are caused by distortion of the central portion of the corona radiata, which is due to a widening of the ventricles. The corona radiata is a fan-shaped network of fibers that weaves through the white matter of the cortex (the top, main section of the brain) and connects with the fibers of the corpus callosum. White matter is white appearing nerve fibers in the brain and spine that help transmit messages fast. The corpus callosum is a large band of nerve fibers in the brain that help the two sides of the brain communicate with each other.

The nerve fibers in the corona radiata send nerve impulses to the legs and the urinary bladder, which is why difficulty walking and difficulty controlling the urge to urinate occurs. The urinary bladder is a hollow, muscular organ in the body that collects and temporarily holds urine until it is ready to leave the body. Dementia results from distortion of the limbic system near the ventricles. The limbic system is an area near the edge of the middle part of the brain that is important for proper memory functioning and for producing emotions.

It should be noted that increased pressure from cerebrospinal fluid in enlarged ventricles applies considerably more force against the brain than the same pressure in normal size ventricles.

HOW MANY PEOPLE DEVELOP NORMAL PRESSURE HYDROCEPHALUS?

Approximately 250,000 people in the United States develop normal pressure hydrocephalus each year.

WHO USUALLY GETS NORMAL PRESSURE HYDROCEPHALUS?

People who develop normal pressure hydrocephalus tend to be elderly individual 60 years and older.

HOW IS NORMAL PRESSURE HYDROCEPHALUS DIAGNOSED?

Unfortunately, normal pressure hydrocephalus is difficult to diagnose. One of the reasons for this is because the tests used to get pictures of the inside of the brain (such as CT scans or MRIs) do not show a pattern that definitively indicates that the condition is normal pressure hydrocephalus and nothing else. CT (computerized tomography) scanning is an advanced imaging technique that uses x-rays and computer technology to produce more clear and detailed pictures than a traditional x-ray. MRI (Magnetic Resonance Imaging) scans produce extremely detailed pictures of the inside of the body by using very powerful magnets and computer technology.

A test known as a cisternogram may show changes of the flow of cerebrospinal fluid in the brain. Specifically, the cisternogram scan may show that the fluid flowed back into the ventricles (openings in the brain that produce cerebrospinal fluid). A cisternogram is a test in which the flow of cerebrospinal fluid can be monitored. This is done by injecting a substance into the cerebrospinal fluid by inserting a needle in the spinal canal. The substance flows throughout the cerebrospinal fluid and emits a signal. A scanner detects the signal and provides information about the flow of cerebrospinal fluid. It should be noted that although cisternograms were used in the past, they are usually not used now days.

Although the results of CT scans, MRIs, and cisternograms may be consistent with normal pressure hydrocephalus, they may also be consistent with other conditions. Thus, these tests are not sufficient for a diagnosis of normal pressure hydrocephalus. CT and MRI scans will usually show widening of the ventricles. However, it is important to note that many normal elderly people have widened ventricles. Another common findings on a CT scan for people with normal pressure hydrocephalus include a normally sized subarachnoid space (see previous section). A CT scan may also show that cerebrospinal fluid is flowing through the ependyma, which is a type of membrane that lines the ventricles of the brain.

On an MRI scan, one may see that the corpus callosum is thinned and pushed upwards. The corpus callosum is a large band of nerve fibers in the brain that helps the two sides of the brain communicate with each other. Also on an MRI, there may be flow voids present in the cerebral aqueduct and third ventricle. A flow void is a loss of signal in a structure that normally has fluid flowing through it, indicating that there is lower than normal levels of fluid in the structure. Remember from above that the cerebral aqueduct is a narrow opening in the brain that connects the third ventricle with the fourth ventricle, allowing cerebrospinal fluid to flow between these two areas.

The frontal horns of the lateral ventricles may appear rounded in patients with normal pressure hydrocephalus. The frontal horns are the front parts on each side of the lateral ventricles. The results of a spinal tap reveal usually reveals that the cerebrospinal fluid pressure is normal. As a result of the difficulty diagnosing normal pressure hydrocephalus, this condition often goes untreated.

In addition to results of brain scans, the main thing that health care providers focus on are the three main signs discussed above. These signs are difficulty walking, difficulty thinking, and difficulty holding in urine. Even these signs, however, are not specific to normal pressure hydrocephalus and can be due to other conditions.

HOW IS NORMAL PRESSURE HYDROCEPHALUS TREATED?

If a cause for normal hydrocephalus can be identified, the condition can often be treated and the effects can often be reversed. The most common type of treatment is called a shunt. A shunt is a flexible tube that is inserted into the ventricle, which drains the extra cerebrospinal fluid.

The most commonly used shunt is called a ventriculperitoneal (VP) shunt because it drains cerebrospinal fluid from the ventricles to the peritoneum. The peritoneum is a layer of tissue that lines the belly and covers most of the organs in the belly. Another type of shunt is a ventriculoatrial shunt, so named because it drains cerebrospinal fluid from the ventricles to the atrium of the heart. Each chamber on the top of the heart is called an atrium

A shunt may be placed even if the physician is not certain that the cause of the patient's problems is normal pressure hydrocephalus. The decision on whether to place a shunt will be based on the results of a clinical evaluation by the doctor and the results of a CT scan. If the condition improves after placement of a shunt, health providers are generally confident that the cause of the patient's problems was normal pressure hydrocephalus. It is worth noting that shunting can help decrease the size of the ventricles in 3 to 4 days even if the hydrocephalus has been present for a year, and sometimes more.

Temporary relief of symptoms may be achieved with a spinal tap or treatment with Acetazolamide (Diamox). Acetazolamide is a diuretic medication that can decrease the production of CSF. A diuretic is a medication that helps to release fluids from the body in the form of urine. There is no definitive evidence yet, however, that medication can effectively treat normal pressure hydrocephalus.

WHAT IS THE PROGNOSIS FOR PEOPLE WITH NORMAL PRESSURE HYDROCEPHALUS?

Prognosis will also depend on whether there are other co-occurring diseases (see above) of the brain present in addition to normal pressure hydrocephalus. In generally, however, prognosis is generally determined by the effectiveness of the shunt. It has been estimated in one large study that only about 21% of patients improve after shunt surgery (see last section). In this same study, approximately 28% of patients experienced some type of complication. Thus, shunt surgery is not a guarantee that significant improvement will occur and is not without risks. On a more positive note, some studies have found that as many as 80 percent of individuals can improve after shunt surgery. The findings differ based on the number of patients, type of patients, causes of hydrocephalus, and operative techniques/procedures used in the study.

Because of the above factors, doctors need some way to determine whether shunt surgery will be effective. This is why a presurgical evaluation is performed in which the patient is given a quick test of cognitive (thinking) abilities and a timed walking test. Afterwards, a needle is inserted into the spinal canal and a significant amount of cerebrospinal fluid is removed. The patient is then readministered the thinking test and asked to do the timed walking test again. A clear improvement in either of these two tests indicated that the patient will respond well to shunt surgery. Decreased urges to urinate or increased bladder control may also indicate that shunting will be an effective treatment. The previously mentioned changes may not occur immediately, but may take 1 to 2 days. The presurgical procedure may be repeated over the next day or two if the patient is a good candidate for a shunt. When presurgical evaluations are performed to select patients for surgery, more than half of the patients can show a significant improvement after the shunting procedure is performed.

If the shunting procedure is performed, it may take about 3 days for symptoms to improve but can take as long as a few weeks. Mental abilities and control of urine improve quicker than walking abilities after a shunting procedure is performed. However, dementia of longer than two years is less likely to reverse. If the shunting procedure was not effective, it may need to be revised with an additional surgery.

If a cause of normal pressure hydrocephalus cannot be identified and/or the shunting procedure does not work, the condition often gets worse and can lead to a progressive dementia and death. Death can occur because the extra cerebrospinal fluid can press on the brainstem, an area of the brain that controls many crucial life functions, such as breathing. One study showed that death and persistent disability occurs in about 7% of patients after shunting.

WHEN WAS NORMAL PRESSURE HYDROCEPHALUS FIRST DESCRIBED?

Normal pressure hydrocephalus was first described in 1965 by Dr. Solomon Hakim while he was training in neurosurgery (surgery of the brain and/or spine) at Massachusetts General Hospital.

HOW IS NORMAL PRESSURE HYDROCEPHALUS ABBREVIATED?

Normal pressure hydrocephalus is often abbreviated in medical charts as NPH.

WHAT ELSE IS NORMAL PRESSURE HYDROCEPHALUS KNOWN AS?

Normal pressure hydrocephalus is also known as occult hydrocephalus and Hakim's disease.

WHAT IS THE ORIGIN OF THE TERM, NORMAL PRESSURE HYDROCEPHALUS?

Normal pressure hydrocephalus comes from the Latin word "norma" meaning "rule," the Latin word "premere" meaning "to press," the Greek word "hydor" meaning "water," and the Greek word "kephale" meaning "head." Put the words together and you have "rule to press water head," which doesn't make much sense in the literal translation unless you read about what it is.