Normal pressure hydrocephalus (NPH) is an accumulation of cerebrospinal fluid that causes the ventricles in the brain to become enlarged with little or no increase in pressure. The name of this condition is misleading, however, because some patients have fluctuations of cerebrospinal fluid (CSF) pressure from high to normal to low. In most cases of NPH, it is not clear what causes the CSF pathways to become blocked.
Adult-onset normal pressure hydrocephalus describes those cases that occur in older adults (age 50 and older). The majority of the NPH population is 60 years or older.
The majority of cases of NPH are idiopathic (meaning unknown cause). In some cases, NPH can develop as the result of a head injury, cranial surgery, subarachnoid hemorrhage, meningitis, tumor or cysts, as well as subdural hematomas, bleeding during surgery, and other infections.
The syndrome of normal pressure hydrocephalus is usually characterized by complaints of gait disturbance (difficulty walking), mild dementia and impaired bladder control.
This can range in severity from mild imbalance to the inability to stand or walk at all. Gait is often wide-based, short-stepped, slow and shuffling. People with NPH may have trouble picking up their feet, making stairs and curbs difficult and frequently resulting in falls. They may also have difficulty turning around, and turn very slowly with multiple steps. Gait disturbance is often the most pronounced symptom and the first to become apparent.
This can be described as a loss of interest in daily activities, forgetfulness, difficulty dealing with routine tasks and short-term memory loss. The cognitive symptoms associated with NPH are usually less severe than full-blown dementia, and are often overlooked for years or accepted as an inevitable consequence of aging. People with NPH do not usually lose language skills, but they may be less aware of their deficits than those around them, and may even deny that there are any problems. Not all individuals have an obvious cognitive impairment. In mildly affected cases, conversational skills may be preserved and thinking abilities may be relatively unchanged. In some cases, cognitive changes may only be detectable with formal neuropsychological testing.
Impairment in bladder control
This is usually characterized by urinary frequency and urgency in mild cases whereas a complete loss of bladder control (urinary incontinence) can occur in more severe cases. Urinary frequency is the need to urinate more often than usual, sometimes as often as every one to two hours. Urinary urgency is a strong, immediate sensation of the need to urinate. This urge is sometimes so strong that it cannot be held back, resulting in incontinence. In very rare cases, fecal incontinence may occur. Some people never display signs of bladder problems.
Because these symptoms are often associated with the aging process in general, and a majority of the NPH population is older than 60 years, people often assume that they must live with the problems and adapt to the changes occurring within their bodies.
When NPH is suspected, one or more of the following tests is usually recommended to confirm the diagnosis and assess the person’s candidacy for shunt treatment.
Clinical exams to evaluate symptoms
This consists of an interview and/or a physical/neurologic examination. Some common tests include discussing and observing walking and turning to determine the extent of and type of gait disturbance; assessing cognition by asking a few questions or administering a full neuropsychological evaluation to probe such qualities as attention, reaction time, memory, reasoning, language and emotional state; and verbally assessing urinary urgency and frequency or incontinence.
Brain images to detect enlarged ventricles
These commonly include magnetic resonance imaging (MRI) and computerized tomography (CT).
Cerebrospinal fluid tests (CSF)
These include lumbar punctures, known as a spinal tap, which allows an estimation of the CSF pressure and analysis of the fluid; external lumbar drainage; measurement of CSF outflow resistance; intracranial pressure monitoring; and isotopic cisternography, which involves having a radioactive isotope injected into the lower back through a spinal tap, to monitor the absorption of CSF over a period of several days.
A shunt is the most common and usually the only available treatment for NPH. A shunt is a flexible tube placed into the ventricular system that diverts the flow of CSF into another region of the body where it can be absorbed, such as the peritoneal (abdominal) cavity or the right atrium of the heart. The shunt tube is about 1/8 inch in diameter and is made of a soft, pliable plastic that is well tolerated by our body tissues. Shunt systems come in a variety of models but have similar functional components. Catheters (tubing) and a flow-control mechanism (one-way valve) are components common to all shunts. The valve in the shunt maintains the CSF at normal pressure within the ventricles.
The surgical placement of a shunt, which is performed by a neurosurgeon, is a relatively short and uncomplicated procedure. The patient is brought to the operating room and is placed under general anesthesia. To ensure cleanliness, a small region of the scalp may be clipped or shaved, and, for a ventriculoperitoneal shunt, the entire area from the scalp to the abdomen is scrubbed with an antiseptic solution. Sterile drapes are placed over the patient. Incisions are made in the head and abdominal areas. The shunt tube is passed beneath the skin, in the fatty tissue that lies just below the skin. A small hole is made in the skull, and the membranes between the skull and brain are opened. The ventricular end of the shunt is gently passed through the brain into the lateral ventricle. The abdominal (peritoneal) end is passed into the abdominal cavity through a small opening in the lining (peritoneum) of the abdomen. This is where the CSF will ultimately be absorbed. The incisions are then closed. When the procedure is completed, sterile bandages may be applied to the incisions and the patient is taken to the recovery room where the anesthesia is allowed to wear off.
There are many unknowns surrounding the diagnosis and treatment of normal pressure hydrocephalus. Although the success rate for shunting can be as high as 80 percent when the cause of hydrocephalus is known, the chance for a complete reversal of symptoms or marked improvement is less predictable. However, NPH is not a hopeless condition. Advanced technology is continually introduced and developed. Adults diagnosed with normal pressure hydrocephalus, and their families, should be encouraged to ask questions, gather information and network with others.
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