Is Shunting Risky for Treating Hydrocephalus?
Updated October 12, 2014.
Written or reviewed by a board-certified physician. See About.com's Medical Review Board.
Hydrocephalus is an enlargement of the spaces in the brain (ventricles) that contain cerebrospinal fluid (CSF). While this is sometimes due to lesions that block the normal flow of CSF and thereby increase pressure in the ventricles, normal pressure hydrocephalus (NPH) is an enlargement with no such explanation.
NPH classically causes a triad of symptoms including dementia, gait changes, and urinary incontinence, all of which may respond to some degree to a neurosurgical intervention that shunts CSF away from the ventricles to another part of the body.
This treatment can be risky, however, and there is little formal agreement on the proper diagnosis of NPH, how to select patients most likely to benefit from shunting, what constitutes a significant improvement after therapy, or the best neurosurgical technique to use.
How Does Shunting Work?
There are different kinds of shunts, but all ultimately have the same goal--to drain CSF from the ventricles into another part of the body. A small hole is opened in the skull and a catheter is run through the brain into the ventricle to drain the fluid.
The catheter exits the skull and runs under the skin to another place in the body. Most shunts are ventriculoperitoneal, meaning they drain CSF into the abdomen, though ventriculoatrial shunts that drain fluid into the heart are also sometimes used.
The flow of CSF is controlled by a one-way valve. In some cases, an additional operation will be needed to adjust the pressure required to open the valve, but some models permit pressure adjustments without another operation.
For example, if a shunt wasn't thought to be draining enough, the pressure needed to open the valve could be lowered, thereby draining more fluid.
Few studies have been done comparing the safety and efficacy of different shunts, and they are generally not of the best quality. In general, little significant difference has been found between models.
How Well Does Shunting Work?
A Cochrane review of shunting in NPH performed in 2009 stated: "There is no evidence to indicate whether placement of a shunt is effective in the management of NPH." That is not to say that studies haven't been done. A review published eight years prior, in 2001, stated that up to 59 percent of patients improved after surgery. The problem, though, is that the quality of the evidence is rather poor.
Case series investigating surgical outcomes in NPH were small and didn't compare those who had surgery with those who did not. The studies varied widely in the criteria used to select patients, which can impact how the patients do after surgery. Studies also differed in how they measured improvement. With so much variation in how data were collected, it's difficult to say with confidence what, if anything, the data actually mean.
Generally, the ability to walk seems to improve most after surgery, but it's difficult to say what percentage of people improve or how substantial that improvement is. Cognitive impairment is more resistant to treatment, but may also improve, especially if it is only very mild. Again, though, the outcome measures vary, and so it's almost impossible to say what percentage of patients improve.
Similar discrepancies exist even for urinary incontinence, though most agree that complete resolution is uncommon, occurring in only 4 of 23 patients one year after surgery in one report.
In short, most studies agree that shunting likely offers some benefit, most of all to walking, but studies differ on just how beneficial the procedure actually is. This is frustrating given the known risks of the procedure.
How Long Do Benefits Last?
Again, there are few studies looking at long-term outcomes after shunting for NPH. In many series that have a year or more follow-up, benefits remain in only about one half of those who initially showed improvement, though some studies show sustained improvement. For example, a study in Baltimore reported more than 60 percent of patients with sustained improvement over six years. Others, though, suggest that the improvement lasts in as little as a third of patients.
Just How Risky is Shunting for NPH?
A 2008 review of shunting in NPH showed an approximate complication rate of 38 percent. Six percent had permanent deficits or death. Repeated operations are also common, with about 53 percent of patients requiring shunt revisions over six years in one study.
The most common serious complication in the first year is a subdural effusion or hematoma, meaning a collection of blood or fluid between the two outermost membranes surrounding the brain. This may result from the tearing of veins in shunt over-drainage. This is rarely serious enough to require further neurosurgery. Shunt infections usually occur in the first month, and require treatment with shunt removal and antibiotics. Other complications can include seizures, intracerebral bleeding, shunt failures, abdominal injury in ventriculoperiteoneal shunts, and arrhythmias in ventriculoatrial shunts.
Because of the potential for complications, regular follow-up and close attention to any symptoms is important after shunt placement.
Who Responds Best to Shunt Placement?
As with most things in the world of NPH, predictions about who will respond best to shunt placement are not absolute. That said, the following things have been proposed to decrease the likelihood of improvement after shunt placement.
- Failure to improve after lumbar puncture or lumbar drain.
- Moderate to severe dementia.
- Unknown cause of NPH, as opposed to that caused by old subarachnoid hemorrhage or infection.
- Long duration of symptoms, especially over two to three years.
- Later development of gait abnormalities
- Signs of small strokes or other vascular disease
- Signs of additional causes of dementia such as Alzheimer's
- Advanced age (especially controversial)
Conclusions:
In short, people are most likely to benefit from shunt replacement when difficulty walking is recognized early and cognitive impairment is mild, when there are no signs of alternative explanations of their symptoms either on physical exam or on studies such as magnetic resonance imaging, and when a procedure such as a lumbar puncture leads to symptomatic improvement. In about half of these patients, though, the benefits of the procedure may not be sustained. Due to the possibility of shunt malfunction or complications, close follow-up will be necessary after neurosurgery.
Sources:
Esmonde T, Cooke C. Shunting for normal pressure hydrocephalus. The Cochrane Library 2009: DOI: 10.1002/14651858.CD003157
Gustafson L, Hagberg B. Recovery in hydrocephalic dementia after shunt operation. J Neurol Neurosurg Psychiatry 1978; 41:940.
Hebb AO, Cusimano MD. Idiopathic normal pressure hydrocephalus: a systematic review of diagnosis and outcome. Neurosurgery 2001; 49:1166.
Klassen BT, Ahlskog JE (2011): Normal pressure hydrocephalus: how often does the diagnosis hold water? Neurology. 77:1119-1125.
Malm J, Kristensen B, Stegmayr B, et al. Three-year survival and functional outcome of patients with idiopathic adult hydrocephalus syndrome. Neurology 2000; 55:576.
Pujari S, Kharkar S, Metellus P, et al. Normal pressure hydrocephalus: long-term outcome after shunt surgery. J Neurol Neurosurg Psychiatry 2008; 79:1282.