Approach
Treatment should be offered as soon as practical after the diagnosis is confirmed by lumbar puncture, prolonged external lumbar drainage, or cerebrospinal fluid (CSF) infusion procedure. There is some evidence that the surgery outcomes are better in patients with shorter symptom duration, and in those for whom surgery is offered early after diagnosis.[27][28] Mortality may also be reduced with early surgical treatment. Early shunt surgery improves survival in idiopathic normal pressure hydrocephalus.[29]
Ventriculoperitoneal shunting is the standard surgery for the treatment of NPH in patients who are assessed as being suitable for surgery.[30] Patients who are not surgical candidates should be offered treatment aimed at controlling their vascular risk factors. Some nonsurgical candidates may additionally be treated with repeated large-volume CSF taps.
Assessment of patient suitability for surgery
Surgery should be considered in patients with a good response to any of the diagnostic CSF procedures, after an assessment of risks and benefits. Early treatment may result in more complete and long-lasting benefits, but diagnostic certainty increases with severity of symptoms, and therefore with disease duration. A short duration of symptoms carries a better prognosis for surgical intervention, but improvement is occasionally seen in those with long-term cognitive difficulties.[27][28]
Response to surgery is variable, but a positive response is less likely in those with extensive radiologic change on neuroimaging.[19][31] Most patients with NPH have significant vascular disease and are at a relatively high risk of perioperative complications such as stroke and myocardial infarction. Age and coexistent cardiovascular disease represent significant operative risks that must be taken into account, and these patients are generally at high risk of anesthetic complications. This, and the unpredictability of the response to shunt surgery, renders patient selection problematic.
Preoperative investigations
Before surgery, patients should have as a minimum:
neuroimaging
a timed walk before and 1 to 3 hours after a large-volume CSF tap, and
cognitive assessment
to confirm the diagnosis and establish the severity of the disorder.
In some centers, the CSF infusion test is available. The primary objective of this test is to assess CSF outflow resistance, which can distinguish patients who are more likely to respond to surgery. Careful consideration of anesthetic risk is mandatory.
Ventriculoperitoneal shunting
Treatment with lifelong CSF shunting provides an alternative low-resistance route for CSF to enter and leave the brain during the cardiac cycle, and thus improves cerebral perfusion.
A catheter is placed into the lateral ventricle under general anesthesia, usually via the nondominant cerebral hemisphere, and the distal end placed in the peritoneal cavity via a line tunneled under the skin. The valve is usually positioned behind the ear. A programmable shunt is used.
Post-surgery checks and complications
After surgery, the shunt valve and subcutaneous catheter should be inspected for signs of infection or breakage. Pumping the valve should elicit prompt refilling of the reservoir after compression. If this does not occur, a proximal obstruction is likely. Difficulty compressing the valve implies distal blockage. If a shunt malfunction is suspected, a shunt series of plain x-rays should be ordered to check for continuity, and a shunt revision may be required.
Common shunt complications include subdural hematoma, mechanical obstruction, and infection, and occur in about 22% of patients.[32] Shunt obstruction may cause a sudden change in walking function, but this may also be due to stroke or subdural hematoma. Obstruction more commonly causes a gradual return of symptoms present before surgery.
Shunt valve pressure, adjustment and revision
The adjustment of shunt valve pressure is contentious. In one double-blind randomized controlled trial, gradual lowering of the valve setting to pressures below 12 cm water was associated with significantly better outcomes (but increased risk of overdrainage) compared with fixed valve setting at a mean of 13 cm water.[32] However, another double-blind RCT failed to find a significant difference in clinical improvement between gradual reduction of the valve setting compared with a fixed valve setting of 12 cm water.[33]
Underdrainage of CSF may produce recurrence of symptoms and hearing loss. Chronic overdrainage of CSF can cause subdural hematoma, headache, and tinnitus. One study found that gravitational valves avoid one additional overdrainage complication in approximately every third patient, compared with other valve types.[34] One cochrane review concluded that the use of flow-regulated or differential pressure-regulated valves did not influence the outcome of shunting in this condition.[35]
Shunt malfunction can often be managed by external adjustment of the valve settings; however, shunt revision is usually required. About half of patients eventually require a shunt revision, and approximately 75% of these patients will respond positively.[31]
Control of cardiovascular risk factors
All patients should also be offered treatment aimed at controlling their vascular risk factors, such as blood pressure control with antihypertensive drugs, smoking cessation, and cholesterol-lowering drugs. See Essential hypertension (Management approach), Smoking cessation (Management approach), and Hypercholesterolemia (Management approach).
Endoscopic third ventriculostomy (ETV)
Unlike shunting, ETV does not require prosthesis implantation. It is considered an alternative option to shunting. However, preliminary results from an open label randomized trial found that shunting is superior to ETV, as it is associated with better functional neurologic outcomes 12 months after surgery.[36][37]
Patients unsuitable for surgery
Patients who refuse surgery, or those who are unsuitable for surgery, should be offered treatment aimed at controlling their vascular risk factors, such as blood pressure control with antihypertensive drugs, smoking cessation, and cholesterol-lowering drugs.
Some patients who refuse surgery, or who are unsuitable for surgery, may respond to repeated large-volume CSF taps, with apparent improvement sustained for weeks or months.
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