Once symptoms of gait disturbance, mild dementia, or problems with bladder control are identified and NPH is suspected, a physician may recommend one or more additional tests. At this point in the diagnostic process, it is important that a neurologist and a neurosurgeon are identified, along with the primary care physician. Their involvement from the diagnostic stage onward is helpful not only in interpreting test results, but also in discussing surgery, follow-up care, and expectations of surgery. The decision to order a given test may depend on the specific clinical situation.
In this test a device uses sound to outline the structures within the skull.
Computed tomography (CT)
This modality creates a picture of the brain by using X-rays and a special scanner. It is safe, reliable, painless, and relatively quick (about 15 minutes). An X-ray beam passes through the head, allowing a computer to make a picture of the brain. A CT shows if the ventricles are enlarged or if there is obvious blockage.
MRI comparison of ventricular size in a (A, B) normal patient and in a (C, D) patient with NPH.
| Illustration of a lumbar puncture
Magnetic resonance imaging (MRI)
This modality is safe and painless and takes about 30 minutes or longer. MRI uses radio signals and a very powerful magnet to create a picture of the brain. It shows whether the ventricles are enlarged, whether CSF flow is blocked, and provides information about surrounding brain tissue. MRI provides more information than CT and is therefore the test of choice in most cases.
Lumbar puncture or spinal tap
This test allows an estimation of CSF pressure and analysis of the fluid. Under local anesthetic, a thin needle is passed into the spinal fluid space of the lower back. As much as 50 cc of CSF may be removed to determine if symptoms are temporally relieved.
Lumbar catheter insertion
This test is a variation of the lumbar puncture. A spinal needle is inserted in the spinal fluid space of the lower back. Then a thin, flexible tube is passed into the spinal fluid and the needle is removed. The lumbar catheter allows continuous recording of spinal fluid pressure or continuous removal of spinal fluid as needed over several days to imitate the effect that a shunt would have. Patients who respond dramatically to such spinal fluid drainage are likely to respond well to shunt surgery.
Intracranial pressure (ICP) monitoring
ICP monitoring requires admission to the hospital. A small pressure monitor is inserted through the skull into the brain or ventricles to measure ICP. The pressure is not always high, and pressure monitoring (either by lumbar catheter or the intracranial method) can detect an abnormal pattern of pressure waves.
Measuring CSF outflow resistance
This test requires admission to the hospital. The test assesses the degree of blockage to CSF absorption back into the bloodstream. It requires the simultaneous infusion of artificial spinal fluid and measurement of CSF pressure. If the calculated resistance value is abnormally high, then the patient has a good chance of improving with shunt surgery.
In this procedure a radioactive isotope is injected into the lumbar subarachnoid space (lower back) through a spinal tap. The absorption of CSF can then be evaluated over time by periodic scanning, which shows whether the isotope is being absorbed over the surface of the brain or whether it remains trapped inside the ventricles. Isotopic cisternography involves spinal puncture and is considerably more involved than either CT or MRI. This test has become less popular because a positive cisternogram does not reliably predict whether a patient will respond to shunt surgery.
In this test, a patient is asked a series of questions. The answers are used to determine if there is a loss of brain function related to hydrocephalus.
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