Authors: Michael D. Cusimano, MD & Carolyn Sawicki
Dr. Michael Cusimano received his MD and PhD from the University of Toronto, his Masters degree from the University of Illinois at Chicago and a Fellowship in Skull Base and Microvascular Surgery from the University of Pittsburgh. Since 1992, Dr. Cusimano has been a Staff Neurosurgeon at St. Michael’s Hospital with a cross appointment at the Hospital for Sick Children and UHN. He has been a full Professor of Neurosurgery, Education and Public Health at University of Toronto since 2005. Dr. Cusimano was the first practicing surgeon in the world with a PhD in Education. He has raised awareness about adult hydrocephalus and NPH since the 1990s, and has been one of Canada’s leading surgeons in the field since then. His opinion in the management of hydrocephalus in adults is widely sought. Dr. Cusimano’s research includes NPH, skull base surgery, brain tumours and aneurysms, quality of life, the cerebellum, neurocognition, injury and preventing injury.
Hydrocephalus is an excessive accumulation of cerebrospinal fluid (CSF) within the head due to a disturbance of its production, flow, or absorption into the venous system1. CSF is produced and secreted bilaterally by the choroid plexuses in the lateral ventricles within the brain. In a healthy individual, the CSF flows from the lateral ventricles into the third ventricle via the interventricular foramina. From there it continues inferiorly into the fourth ventricle via the aqueduct of Sylvius. Once it reaches the fourth ventricle, it flows into the subarachnoid space where absorption into the venous sinuses takes place by means of arachnoid villi. When the flow of CSF between these regions is disturbed in any way, hydrocephalus may occur, causing increased intracranial pressure (ICP). Consequently, the type of hydrocephalus that ensues is dependent on how the disturbance of flow takes place.
The classification of hydrocephalus can be split into two main categories: communicating hydrocephalus and non-communicating hydrocephalus (also known as obstructive hydrocephalus). Communicating hydrocephalus, where the flow of CSF remains undisturbed, can occur as a result of overproduction of CSF, defective absorption of CSF, or insufficient venous drainage2. Alternatively non-communicating hydrocephalus occurs when the flow of CSF is disrupted. This type of hydrocephalus has many causes including congenital malformations (e.g. aqueductal stenosis), inflammation, hemorrhage, and mass lesions2. Each of these classifications can fall under the category of either congenital (present at birth) or acquired (developed later in life) hydrocephalus.
As the cause of hydrocephalus is so diverse, diagnosis may be difficult in some cases. Most notably, issues surrounding the diagnosis of Normal Pressure Hydrocephalus (NPH) persist. When a patient develops the symptoms of gait disturbance, urinary incontinence and cognitive disturbances, has communicating hydrocephalus, normal CSF pressure on lumbar puncture, and an absence of papilledema (a sign in the eyes indicating swelling of the optic nerve), doctors consider the diagnosis of NPH3. This particular type of hydrocephalus can be classified as either Secondary Normal Pressure Hydrocephalus (SNPH) or Idiopathic Normal Pressure Hydrocephalus (INPH). SNPH most commonly develops after traumatic subarachnoid hemorrhage and other insults, such as meningitis, that most likely interfere with CSF absorption around the surface of the brain and spine in areas called the arachnoid granulations3. In cases where the cause of the NPH is of unknown origin it is referred to as “idiopathic” NPH or “INPH”.
Estimates as to how many people have INPH vary widely. One study suggested that more than 750,000 Americans have NPH, but less than 20% receive an appropriate diagnosis and treatment4. Another study indicated that 2.2 people per million people in the USA have the condition5 (about 600-700 people in the whole country as opposed to 750,000!). Marmarou et al.6 investigated four nursing homes through a retrospective chart review and estimated that the incidence of INPH varies between 9-14% in assisted-living facilities for the elderly. Another study indicated that 2-6% of patients with dementia and about a third of people with “reversible” dementias have INPH7. Yet another study indicated that 5-10% of dementias are a result of INPH4. These widely varying estimates are likely the result of different means of diagnosing the condition.
Since INPH is a syndrome (i.e. a collection of symptoms), the diagnosis can often be a difficult one to make due to a variety of diseases giving rise to each of the symptoms in the “triad” (i.e. gait disturbance, urinary incontinence and cognitive difficulties)4. For example, gait disturbances can be caused by a variety of diseases ranging from arthritis of the hip or knee to Parkinson’s Disease. Likewise, urinary incontinence can be caused by conditions as diverse as urinary tract infections and benign prostatic hypertrophy. Similarly, cognitive disturbances can be associated with side effects to medications and depression amongst a whole variety of conditions. The astute clinician must consider all these alternative diagnoses in coming to a diagnosis of INPH. In addition, because INPH usually presents in older persons, they are often affected by a number of these competing diagnoses, which can make the diagnosis even more challenging8.Since NPH was first described in the 1960s, no definitive method has been developed to confirm its diagnosis and the “gold standard” remains clinical improvement with CSF shunting3,9. However in 2005, criteria for the diagnosis of INPH were published to place patients who have not yet been shunted into three categories: “probable”, “possible”, or “unlikely” INPH. In order for the INPH to be categorized as “probable” INPH the patient must meet the following criteria: be older than 40 years of age, have insidious progression of symptoms over a period of three months, have CSF opening pressure between 70 and 245 mmH2O, the CT or MRI must show an Evan’s index of at least 0.3 (Figure 1) as well as either temporal horn enlargement, periventricular signal changes, periventricular edema, or an aqueductal/fourth ventricular flow void10. Clinically, the patient must demonstrate gait dysfunction in addition to either urinary incontinence or cognitive dysfunction. Abnormal urinary urgency or frequency is sufficient to document urinary incontinence. Cognitive dysfunction is defined as impairment of two or more domains such as psychomotor speed, fine motor speed or accuracy, attention, short-term recall, executive function, or behavioral/personality change10.
In order for the INPH to be categorized as “possible” INPH, the patient must have the following criteria: be below the age of 40 years or have symptoms for less than three months, have unavailable or abnormal CSF opening pressures, have non-progressive symptoms or cerebral atrophy severe enough to explain ventriculomegaly and they usually have papilledema or symptoms explicable by other causes10. Patients with “unlikely” INPH usually have papilledema or symptoms explicable by other causes and have no ventriculomegaly and no component of the clinical triad10. Although these descriptions are helpful to a degree, the absence of properly designed, well-controlled studies regarding diagnosis and treatment continue to plague the field. Clinicians must act on class II and III data6 and there is a great need for several prospective randomized clinical trials around the diagnosis and treatment of INPH.
Patients who meet either the clinical criteria for “probable” or “possible” INPH should be referred to a neurologist for a full cognitive and gait assessment as well as a lumbar puncture to assess opening pressure and whether the drainage of a large volume of CSF has any effect on their symptoms. CSF drainage involves a lumbar puncture to withdraw CSF (40-50 cc as lesser volumes have low sensitivity). Gait and/or cognition are measured before and after the test, with improvement indicating that the patient may benefit from surgery6. However, CSF lumbar drainage, the so-called “tap test”, has a high false negative rate. Thus, absence of improvement after the test does not mean that the patient will not necessarily improve with surgery. The neurologist may also wish to perform other tests such as CSF infusion tests, radionucleotide cisternography, or CSF blood flow studies.
Increasingly popular in helping to define who might improve with CSF diversion surgery is a trial of CSF External Lumbar Drainage (ELD). ELD involves introduction of a spinal catheter into the lumbar subarachnoid to provide extended drainage of CSF at a rate of approximately 10mL/h for 37 to 72 hours, providing the sensitivity and specificity (50%-100%)6,8. A retrospective study that examined shunting procedures for NPH from 1993 to 2003 found that NPH could be accurately diagnosed with continuous CSF monitoring and a three-day trial of controlled (10 mL per hour, 240 mL per day) continuous CSF drainage4,11. However, ELD is much more invasive than CSF drainage and the administration time is significantly greater. The risk of meningitis varies from 4-12% and there is a 0.2% risk of death reported with the procedure12,13.
Once the diagnosis is made and the patient is referred to neurosurgery, the doctor must decide whether shunt insertion is the best option. Since shunt insertion is a long-term commitment to an imperfect device, the potential risks and benefits within a particular patient are essential to consider for every individual. In cases of secondary hydrocephalus or aqueductal stenosis, an endoscopic third ventriculostomy may be a better first option than a shunt. In someone with advanced cognitive difficulties and gait disturbances, reversing the condition may be less likely, which then increases the weight of the potential risks involved. Other factors determined by the patient’s history (e.g. a history of alcohol abuse, a history of cardiovascular disease) and physical examination (e.g. severe peripheral neuropathy) must be carefully considered.
Once shunt insertion has been determined to be the best option, the surgeon must decide which type of shunt to insert and with what kind of valve. Historically, ventriculoatrial (VA) shunts were more popular because of the high incidence of plugging with ventriculoperitoneal (VP) shunt from polyethylene composed peritoneal catheters. With the development of Silastic tubing in the late 1950s and the success of its use in the 1960s, VP shunts once again became popular14. In addition, VP shunts are preferable due to ease of placement and lower frequency of severe complication. However, in cases of severe abdominal pathology, VA shunting may be favourable14. Once a shunt valve has been selected, the next step is to decide which shunt valve best suites the patient’s needs.
There are many different types of shunt valves and each has its own advantages and disadvantages. Fixed differential pressure valves (DPVs) are comprised of a simple, lower cost mechanism that regulates fluid flow by the different pressure that exists between the inflow and outflow sections of the valve15. The valve can be chosen as a low, medium, or high pressure valve, but once inserted it cannot be reset without another surgery. Low pressure valves have been shown to be superior in reducing ventricular size after shunting. This fact may be a primary consideration in INPH where an improvement in the clinical condition can be associated with stable ventricular size. In contrast, a valve in which the pressure can be adjusted after installation is called a programmable valve. It has been reported that 36-75% of patients do indeed get the pressure adjusted post shunt insertion15. With flow regulated valves, internal resistance changes automatically with pressure thus better adapting to different conditions. Gravity assisted valves are position-sensitive and contain two systems of CSF flow in the horizontal and vertical position15. This type of valve has been reported to be useful for patients with NPH due to its ability to automatically regulate to physiological drainage independent of the physical position of the patient15. Antisiphon devices may be added (some valves have them built in) to prevent excessive removal when sitting and standing15. In cases where shunt insertion is not viable, alternatives such as endoscopic third ventriculostomy should be considered.
Endoscopic third ventriculostomy (ETV) involves making a small hole in the floor of the third ventricle. This redirects the disturbed CSF flow caused by an obstructed pathway distal to the third ventricle directly into the subarachnoidal space of a basal cranial cistern, and from there to its site of physiological reabsorption16. Some authors believe that it may alter CSF dynamics sufficiently to be useful in cases of communicating hydrocephalus, but this is still controversial17. It is a safe, simple, and effective treatment with an acceptable level of risk of complication in most patients. In recent years it has gained popularity due to improved endoscopic optics, high intensity lighting systems, and miniaturized charged coupled device (CCD) cameras18,19. The benefits of this procedure include shorter operative time and, perhaps most importantly, it mimics CSF dynamics without implanting foreign material20. Although the research clearly points to the advantages of this surgery, a recent survey found that it was only used in 13% of patients, pointing to the wide discrepancy in its acceptance among neurosurgeons21. This technique is only appropriate for patients who have sufficiently large ventricles (>5mm) and foramena of Monroe so as to be able to introduce the endoscope to navigate into the third ventricle22.
In those patients with adequately-sized ventricles, the success of ETV is dependent on the type of hydrocephalus. Recent research has shown that ETV is indicated in the treatment of aqueductal stenosis, obstructive hydrocephalus with a history of hemorrhage or infection, Dandy-Walker malformation, hydrocephalus due to intraventricular hematoma, and hydrocephalus caused by mass effect from tumors17,22,23. In contrast to hydrocephalus caused by an obstruction, the indications for ETV in patients diagnosed with NPH are not significantly defined17. The mainstay of treatment for NPH has been VP shunting, however more recently evidence has suggested a potential role for ETV24. Isolated studies have shown that ETV can have good results in certain cases of INPH but they need to be replicated by other authors11,17. In communicating INPH and SNPH, shunts remain the preferred treatment11,19. In terms of communicating hydrocephalus, the traditional treatment is shunt placement, but high failure rates and numerous complications with this therapy have been reported leading to further research involving ETV19. Recently there have been several preliminary reports of successful treatment with ETV however the role of this procedure for communicating hydrocephalus, at this point in time, remains poorly studied and understood19,25. As with shunt placement, the success of ETV is dependent on the type of hydrocephalus that is inflicting the patient.
In the long-term, INPH has shown to have a good prognosis when treated with a shunt. In 2002, a study followed 51 patients for five years post shunt insertion and found that patients with the complete clinical triad were most likely to respond to surgery26. Of the triad, gait showed the most improvement (47% of patients) and urinary incontinence showed the least (29% of patients)26. Another study in 2008 performed clinical and radiological evaluation 1, 3, 6, and 12 months after shunt surgery and annually thereafter on NPH patients. Again, gait showed the greatest improvement and urinary incontinence showed the least26. The extended nature of the follow-up in this study allowed the researchers to conclude that there is a subset of patients who are capable of sustained improvement for as long as seven years post surgery. The difference between those with sustained improvement and those whose condition worsens is likely related to the selection criteria implemented in choosing candidates for shunt placement and the severity of the clinical triad before surgery.
Each component of the clinical triad shows different rates of improvement post surgery. Cognitive improvement is heavily influenced by the extent of cognitive impairment prior to shunt surgery; those who are severely impaired will likely never recover full function11. In one study, 52% of INPH patients had significant improvement in their overall cognitive outcome three months after shunt surgery11. Typically, improvement in cognition ranges from 29% to 80% and gait and urinary incontinence improve 58% to 90% and 20% to 78% respectively15. There is a large range in the data, which likely points to the discrepancy in choosing candidates for shunting, the variation in the duration of follow-up and different outcome scales used to measure improvement.
Further evidence for long-term outcome after shunt surgery in INPH patients was provided when outcomes following surgical treatment of INPH were prospectively investigated in 200827. Follow-up was performed at three, four, and five years after implantation. It was seen that the percentage of patients experiencing good or excellent outcome remained relatively stable up to five years, however the proportion with poor outcome increased over time. Furthermore, it was found that high success rates tend to occur when good selection criteria are implemented (e.g. NPH guidelines)26. The improved treatments and resulting prognosis is putting a greater emphasis on the need for long-term care.
Adults with hydrocephalus have numerous healthcare and social needs. Access to a neurosurgeon, a family doctor who is aware of hydrocephalus, a neuropsychologist, urologist, geriatrician, social worker, physiatrist, and others may help the patient and her/his caregiver achieve the highest possible quality of life. Some clinics have been established to standardize and enhance the care for adult patients with hydrocephalus24. Not all patients require attention on a yearly cycle; rather, patients should be typically assessed on a schedule that parallels the perceived difficulties associated with their hydrocephalus management. The needs of adults with hydrocephalus however are not just medical. Vocational or retirement counseling is essential, as employment and financial independence is linked to well-being24. As well, providers should be cognizant of autonomy, independent living, social integration, transportation, childcare, insurability, psychological, and/or behavioural services as these are areas that may be problematic for those with hydrocephalus.
Overall, the literature indicates that the success of ETV in an adult population with all forms of hydrocephalus varies from 58% to 87% and in terms of the clinical triad, gait tends to show the highest rate of improvement17,23. Complications are reported to range from 0% to 20%, which is lower than after shunt surgery20,22. The short-term outcome of ETV has been well documented, however it is a relatively new procedure and so long-term studies that are well controlled are needed to assess the value of ETV in adults with different forms of hydrocephalus.
Spina bifida and hydrocephalus, specifically congenital hydrocephalus, are two conditions that present together 90% of the time in childhood and persist into adulthood28. Patients with both of these conditions tend to have compromised physical function, impaired cognitive processes, and reduced opportunity for full social integration and employment28. Physical impairments are generally caused by brain dysmorphology and spinal lesions; these often present as motor and sensory deficits of the lower limbs29. This can result in difficulties with stance and locomotion as well as urinary and bowel dysfunction, which may lead to wheelchair dependence30. It has also been shown that hydrocephalus increases the chance of poor cognitive outcome in adults with spina bifida29. Young adults with spina bifida and hydrocephalus tend to have compromised motor, speech, math deficits as well as poor attention, memory, strategy, and language skills28,31,32. All of these factors contribute to limit functional independence that manifests socially as low levels of employment and high dependence on others. Additionally, studies have shown that functional independence is related to level of lesion on the spinal cord. If the lesion is at the level of L3 or below, the patient is likely to be independent for almost all activities33. As individuals with both spina bifida and congenital hydrocephalus have been inflicted since birth, the nature of their symptoms and treatment are quite different as compared to those who are diagnosed with the condition later in life.
Although congenital and acquired hydrocephalus fall under the same condition, the temporal differences in their onset result in two dissimilar disorders. Cognitive dysfunction is more widespread in individuals with congenital hydrocephalus; damage occurs early on and these patients are never given the opportunity to develop normal functioning32. In contrast, individuals with acquired hydrocephalus are generally able to retain better cognitive functioning because they possessed normal cognitive functioning for a period of time. Patients with acquired hydrocephalus also tend to have had fewer shunt revisions, which is related to better cognitive functioning34.
Since the etiologies of congenital and acquired hydrocephalus are so different, they each require specific health care. However in the case of congenital hydrocephalus, medical and surgical needs for adults with child-onset hydrocephalus often go unaddressed35. This is because past adult healthcare providers have not needed to be familiar with pediatric conditions such as hydrocephalus, and current adult medicine programs lack a dedicated curriculum35. As the prognosis for child-onset hydrocephalus improves, transition care programs that facilitate the transition from pediatric medicine to adult medicine are needed. Shunt malfunction is one of the most pertinent issues of which both pediatric and adult doctors need to be cognizant, however it is clearly not the only one. As children transition to adulthood, other aspects of care such as issues around sexuality, education, and vocations need to be addressed. Support groups such as the Spina Bifida and Hydrocephalus Association of Ontario can be very helpful in navigating and advocating for patients and families.
In the past few decades, a resurgence of research has occurred in the field of hydrocephalus and this aims to improve diagnostic techniques, implement new treatments, and investigate the long-term effects of the condition. Future directions should include a number of randomized controlled trials of diagnostic and therapeutic approaches to INPH. As well, with a growing number of childhood hydrocephalus patients reaching adulthood, more attention should be paid to long term needs and to transition programs.
IMPORTANT RESEARCH: Dr. Cusimano is doing vital research in Normal Pressure Hydrocephalus (NPH) and you might be able to help.
He is currently recruiting individuals who are OVER THE AGE OF 60 and who DO NOT HAVE NPH. This group is for comparison to the group of people with NPH already included in the study.
If you meet those criteria and would like to be a part of this research study, please contact SB&H.
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