Epidemiology

A close examination of the current literature on pediatric and adult hydrocephalus highlights the paucity of scientific data, especially in the adult hydrocephalus arena. There are approximately 10 articles dealing with pediatric hydrocephalus for every publication on adult hydrocephalus. Therefore, much more is known about the incidence, prevalence, epidemiologic factors, inpatient hospitalization, health care costs, and mortality associated with the treatment of hydrocephalus in children. Simon and associates estimated that there are approximately 38,000 to 39,000 admissions for hydrocephalus each year in the United States, with approximately 400,000 hospital days and $2 billion per year in charges for admissions alone for the care of pediatric hydrocephalus.³ The authors found that pediatric hydrocephalus accounts for more than three times the inpatient utilization but just 4% of the National Institutes of Health (NIH) funding for a comparable chronic disease such as cystic fibrosis. Studies such as this help quantify potential impediments to the progress of pediatric hydrocephalus research in the hope of bringing this disparity to the attention of the NIH.

Tisell and coworkers conducted a cross-sectional study in Sweden to evaluate the incidence of adult hydrocephalus from 1996 through 1998.⁴ During that time, they found 891 new adult patients in whom hydrocephalus was diagnosed and treated. This represents an incidence of 3.6 per 100,000. They also found that the incidence was increasing over the 3 years of study. In a North American setting, Patwardhan and Nanda used the Nationwide Inpatient Sample database to determine that 8305 new cases of pediatric and adult hydrocephalus were treated in 2000 in the United States.⁵ This study also estimated an inpatient mortality of 2.7% for hydrocephalus and an overall cost to the health care system of $1.1 billion in 2000. Bondurant and Jimenez used a similar database to estimate the overall prevalence of hydrocephalus in the United States to be 125,000 in 1988, with 36,000 cerebrospinal fluid (CSF) shunt operations being performed each year.⁶ Neither of these studies, however, addressed adult hydrocephalus specifically because the pediatric cohort was intermingled with the adult cases.

One common theme between the pediatric and adult hydrocephalus populations is that they both include a heterogeneous group of hydrocephalus subtypes; however, the causes and incidences of these subtypes differ vastly between children and adults. Unpublished data from the Hydrocephalus Clinical Research Network, which is a five-center network dedicated to studying pediatric hydrocephalus, indicate that the five most common causes of pediatric hydrocephalus are intraventricular hemorrhage (IVH) resulting from premature birth (22%), myelomeningocele (14%), posterior fossa tumor (9%), aqueductal stenosis (8%), and congenital communicating hydrocephalus (8%). These prospective data represent only new diagnoses of hydrocephalus and will be published in detail in the near future. In contrast, Tisell and associates found that the most common causes of adult hydrocephalus were normal-pressure hydrocephalus (NPH) (47%), acquired communicating high-pressure hydrocephalus from bleeding such as after subarachnoid hemorrhage (15%), adult-onset aqueductal stenosis (10%), other noncommunicating hydrocephalus (e.g., tectal glioma) (9%), and acquired communicating hydrocephalus from trauma (5%).⁴ However, these incidences are not stagnant. Technologic advances to improve the care of pediatric patients with hydrocephalus have begun to translate into diminished mortality. Thus, many hydrocephalic children reach adulthood, which makes treatment of the adult cohort perhaps more complex.³

Use of Endoscopic Third Ventriculostomy

Another major difference between pediatric and adult hydrocephalus is that ETV is much more commonly used and therefore much more frquently described in the literature in the pediatric context. For instance, Drake reviewed the cases of 368 patients who had undergone ETV in Canada during a 15-year period.⁷ Analysis of this cohort demonstrated that younger age was associated with ETV failure whereas other factors, including etiology, surgeon experience, previous surgery, and center volume, were not. No similar studies have been conducted in the adult cohort, although there is a burgeoning literature on the role of ETV in patients with NPH. This specific issue is explored later in this chapter.

Late-Onset Idiopathic Aqueductal Stenosis

LIAS, also known as delayed or compensated aqueductal stenosis, is a triventricular hydrocephalus with little or no flow through the aqueduct of Sylvius and a normal to small fourth ventricle. This form of hydrocephalus occurs in adult patients in the absence of space-occupying lesions or previous central nervous system insults (e.g., previous meningitis). LIAS is the cause of approximately 3% to 10% of all adult cases of hydrocephalus.^18,19 In a meta-analysis of 190 patients, Tisell found that the clinical symptoms included headaches (70%), cognitive impairment (55%), urinary incontinence (40%), gait disturbance (28%), diplopia (15%), and endocrine dysfunction (12%).¹⁹ Fukuhara and Luciano evaluated 31 patients and added papilledema, swallowing difficulty, Parinaud’s syndrome, and seizures to this list.¹⁸ Interestingly, patients tended to dichotomize into either a younger cohort (mean age of 33 years) who had primarily headache and signs and symptoms of raised intracranial pressure or an older cohort (mean age of 63 years) with larger ventricles and NPH-like symptoms (cognitive impairment, urinary incontinence, and gait disturbance).¹⁸

Patients with LIAS respond to ETV if properly selected on the basis of signs and symptoms, radiologic findings of triventricular hydrocephalus, and minimal subarachnoid spaces. Success typically results in complete or nearly complete resolution of preexisting signs and symptoms and no need for further CSF diversion procedures. The preponderance of the literature suggests that the success rate of ETV in these patients is 50% to 86.5%, with most authors reporting a success rate of approximately 80% with 6 to 22 months of follow-up.^10,17,18

Secondary Noncommunicating Hydrocephalus

Secondary noncommunicating adult-onset hydrocephalus is defined as obstructive hydrocephalus resulting from a lesion impeding the CSF pathway.¹⁷ The first choice for such lesions is removal or partial resection to reestablish CSF flow; however, in many cases this is not possible or warranted. In such cases, ETV may provide an alternative.

Pineal region tumors, tectal gliomas, and posterior fossa tumors are the most common types of mass lesions causing secondary noncommunicating hydrocephalus in adults. Rare entities such as thalamic masses, cerebellar infarction, and neurocysticercosis have also been described.^20,21 Dusick and colleagues reviewed a series of 108 adult patients who underwent ETV for the treatment of hydrocephalus and found that a mass lesion was an indication for the procedure in 47 (43.5%).²² Their overall success rate for this indication was 76.6%, although the 8-month median follow-up was short. In their study, pineal region masses were the most prevalent indication for ETV, and the success rate in these cases was 71%. These results are compatible in both incidence and success rates with other similar studies.^23–25 Even higher success rates of 81% to 88% are seen for ETV performed to treat patients with tectal gliomas, although 18% of these patients may require a second ETV for ostomy blockage.^9,26 Tectal gliomas are uncommon and, in general, are the indication for only about 4% of all ETVs—both pediatric and adult.²⁶ Arachnoid cysts, especially those found in the suprasellar, prepontine, third ventricle, or posterior fossa region, can often cause obstructive hydrocephalus. Dusick and associates found that ETV was successful in treating this cause of hydrocephalus in 86% of patients.²²

Frequently, ETV performed for tectal and pineal region masses is paired with endoscopic biopsy of the lesion through the third ventricle. Despite a high success rate of the ETV procedure itself, diagnostic rates for the masses are generally lower (69% to 90%). Complication rates associated with the biopsies are typically documented at approximately 18%.^8,23 Common complications of these types of biopsies include intracerebellar and intraventricular hemorrhage, upgaze palsy, ventriculitis, and disturbances in sodium balance.²³

Normal-Pressure Hydrocephalus

NPH is a very controversial subject in the neurosurgical literature in both its diagnosis and its treatment. It is characterized by gradual blockage of the drainage of CSF, which causes a slow buildup of fluid and a less dramatic increase in fluid pressure. Patients with NPH are, in general, elderly patients with a triad of clinical signs and symptoms, including gait abnormalities such as a “magnetic” or “festinating” gait, bladder incontinence, and cognitive impairments or dementia. Findings on magnetic resonance imaging (MRI) include ventriculomegaly, focal enlargements of the subarachnoid space, and an open aqueduct.¹⁷ Most authors use an open aqueduct as a necessary criterion for the diagnosis of NPH. A normal-sized fourth ventricle is seen in 35% of patients with an open aqueduct, whereas it is slightly enlarged in 37% of patients and grossly enlarged in 27%.²⁷

The diagnosis of NPH can be supported by formal neuropsychological testing, gait testing, clinical improvement after a lumbar CSF tap test²⁸ or an external CSF lumbar drainage test,¹⁷ or a high-pressure steady-state plateau found on a lumbar infusion test.²⁸ There is as yet no consensus on which of these tests either defines the diagnosis or predicts good outcomes after CSF diversion.

The use of ETV is relatively new and controversial for the management of NPH. Detractors of its use in this context note that CSF shunts have a high success rate in patients with NPH^17,29,30 and ETV does not lower intracranial pressure enough to maximally improve clinical outcomes. Proponents emphasize that use of ETV will enable these patients to be free of hardware and point out that CSF shunts cause frequent complications in these patients, including infection, overdrainage symptoms, a need for revision, and subdural hematomas.²⁹