The Role of Endoscopic Third Ventriculostomy: A Critical Review

This chapter includes an accompanying lecture presentation that has been prepared by the authors: .

Key Concepts

Careful patient selection is essential in maximizing the chances of success and minimizing the complications inherent to endoscopic third ventriculostomy (ETV).
The ETV Success Score (ETVSS) is a valuable clinical tool available to assess pediatric patients.
The five most common causes of pediatric hydrocephalus are intraventricular hemorrhage resulting from premature birth (22%), myelomeningocele (16%), posterior fossa tumor (11%), aqueductal stenosis (8%), and congenital communicating hydrocephalus (8%).
The four categories of adult hydrocephalus are transition (treated before 18 years old) (17%), unrecognized congenital (congenital pattern, not treated before 18 years old) (27%), acquired (18%), and suspected idiopathic normal-pressure hydrocephalus (iNPH) (39%).
There is growing literature that ETV plus choroid plexus coagulation (CPC) is an effective treatment for hydrocephalus in the infant population (<2 years old).
MRI is recommended both preoperatively and postoperatively to evaluate ETV patients; recommended sequences include sagittal constructive interference in steady state (CISS)/fast imaging employing steady-state acquisition (FIESTA) to assess the floor of the third and prepontine membranes, and a postoperative midsagittal (thin 2-mm cuts) and T2-weighted two-dimensional fast spin echo sequence to evaluate ostomy patency and flow.
Repeated neuropsychological testing is recommended for all patients with hydrocephalus, but especially for ETV patients who tend to maintain larger treated ventricle sizes.

The daily incorporation of the endoscope into neurosurgical practice represents a paradigm shift toward a minimally invasive surgical approach to neurological disease. The ability to view deep-seated cerebral target structures with close-up and wide-angle views has revolutionized the surgical management of ventricular, sellar, and parasellar disease. In this chapter, we review the use of endoscopic third ventriculostomy (ETV) in both adult and pediatric patients with hydrocephalus.

Comparison of Adult and Pediatric Hydrocephalus

Epidemiology

Despite the sizeable societal effect of adult and pediatric hydrocephalus, the current literature has a dearth of scientific data on hydrocephalus in adults. Much more is known about the incidence, prevalence, epidemiologic factors, inpatient hospitalization, health care costs, and mortality associated with hydrocephalus in children. Simon and colleagues estimated that there are nearly 40,000 admissions for hydrocephalus each year in the United States, with approximately 400,000 hospital days, and $2 billion per year in hospital charges for the care of pediatric patients with hydrocephalus alone. This does not account for the additional out-of-hospital care costs or for the adult and elderly population demographics. All demographics were included in a study by Patwardhan and Nanda that used the Nationwide Inpatient Sample database to ascertain that 8305 new cases of hydrocephalus in pediatric and adult patients were treated in the United States in 2000. The overall cost to the health care system was estimated to be $1.1 billion in 2000 alone. Although hydrocephalus accounts for more inpatient utilization than do comparable chronic conditions such as cystic fibrosis, Gross and colleagues found that it receives only 4% of the National Institutes of Health (NIH) funding. Studies such as this have identified pediatric hydrocephalus as an area that needs greater research efforts. After confirming these results in the NIH Research Portfolio Online Reporting Tools (RePORT) database, Gross and associates recommended that researchers consider partnerships, when appropriate, with small businesses, as well as other non-NIH sources of funding to propel hydrocephalus research forward.

Isaacs and colleagues, in a systematic review and meta-analysis, found the overall global hydrocephalus prevalence to be 85 per 100,000. On examination by age category, a bimodal distribution was seen; the worldwide prevalences in the pediatric and elderly populations (≥65 years) were 88 per 100,000 and 175 per 100,000, respectively, but the prevalence increased in those older than 80 years to greater than 400 per 100,000. In the pediatric population, the prevalence was almost 2 times greater in Africa (104 per 100,000) than in North America (55.6 per 100,000). Also, the prevalence of hydrocephalus in the elderly population in Asia was 10 times greater (656.9 per 100,000 compared with 52.8 per 100,000 in North America and Europe).

The causes and incidences of hydrocephalus differ vastly between children and adults. The Hydrocephalus Clinical Research Network (HCRN), which is a 14-center network dedicated to studying pediatric hydrocephalus, conducted a prospective five-center study of more than 1000 children that indicated that the five most common causes of pediatric hydrocephalus were intraventricular hemorrhage (IVH) resulting from premature birth (22%), myelomeningocele (16%), posterior fossa tumor (11%), aqueductal stenosis (8%), and congenital communicating hydrocephalus (8%). In 2014 the Adult Hydrocephalus Clinical Research Network (AHCRN) was established and is now composed of eight North American and European centers. During the AHCRN’s first 2 years, 517 adult patients were prospectively enrolled to examine patient characteristics and demographics. The four categories of adult hydrocephalus were (1) transition (treated before 18 years old), (2) unrecognized congenital (congenital pattern, not treated before 18 years old), (3) acquired, and (4) suspected idiopathic normal-pressure hydrocephalus (iNPH). The iNPH group comprised 38.7% of the enrolled patients, followed by the unrecognized congenital (26.5%) group. Transition and acquired groups comprised 16.6% and 18.2%, respectively.

Patient Selection and Outcomes for Endoscopic Third Ventriculostomy

Pediatric Hydrocephalus

The overall success rate of ETV is between 50% and 90% at 1 year, primarily because hydrocephalus has such a heterogeneous set of causes, which vary with the age of the population being studied. For example, the success rate of ETV in children with hydrocephalus secondary to tectal gliomas is 88%, whereas ETVs done in the context of IVH associated with prematurity succeed in only 0% to 33% of cases. ^, Therefore careful patient selection is essential for maximizing the chances of success and minimizing the complications inherent in ETV.

Young age (less than 6 months) is associated with a lower success rate, independent of the cause; however, this age effect either plateaus or diminishes after the age of 2 years, perhaps because of cranial maturation. ^, For example, because the cranial sutures remain open in infants, the development of elevated intracranial pressure (ICP) may lead to an increased head circumference resulting in a lower pressure gradient across the arachnoid villi, adversely affecting cerebrospinal fluid (CSF) absorption. ^, The literature indicates that the success rate for ETV is high in patients older than 2 years with noncommunicating hydrocephalus caused by aqueductal stenosis, tectal glioma, and posterior fossa tumors. ^, On the other hand, the success rate in patients with hydrocephalus caused by IVH in association with prematurity or postinfectious hydrocephalus appears to be lower; thus its use in these populations is somewhat controversial. ^, ^,

In 2009 Kulkarni and associates evaluated 618 pediatric patients who underwent ETV procedures in 12 pediatric institutions and used the data to develop the ETV Success Score (ETVSS) for pediatric hydrocephalus patients. According to a regression model developed from a training set and later confirmed in a validation set, age, cause of hydrocephalus, and the existence of a previous CSF shunt are important and independent factors in predicting ETV success ( Fig. 45.1 ). Older patients with primary pathologic process near the region of the aqueduct of Sylvius without a history of previous ventricular shunting tended to have the most favorable prognosis. The ETVSS is now used preoperatively at many institutions for pediatric (<18 years of age) patient evaluation and counseling; its use has not been validated in the adult population.

Figure 45.1, The Endoscopic Third Ventriculostomy Success Score can be calculated to closely approximate the percentage possibility of successful endoscopic third ventriculostomy (ETV).

Kulkarni and colleagues published a prospective multicenter study with the HCRN evaluating predictors of ETV success, complications, and morbidities. A total of 336 pediatric patients met inclusion criteria, with the most common causes being aqueductal stenosis (24.8%), midbrain tumors (21.2%), and posterior fossa tumors (14.4%). Severe complications were rare, with less than 2% of patients developing meningitis or a new neurological deficit. The failure-free survival rate at 6 months was 64.8%. The probability of a successful ETV was associated with the ETVSS and the ability to visualize a naked basilar artery intraoperatively.

Adult Hydrocephalus

ETV outcome studies in the adult population lack in comparison to the pediatric literature. However, recent studies have addressed this gap. Hamilton and colleagues performed a retrospective review of 163 adult symptomatic hydrocephalus patients with a mean duration of follow-up of 8.2 years. Primary ETV patients (first treatment being ETV) were compared with secondary ETV patients (shunt malfunction converted to ETV). ETV success, defined by symptomatic improvement, was higher in the primary group (87% versus 65%, P < .001). Zwimpfer and colleagues applied a more quantitative approach to examining improvement after an ETV in adult patients with obstructive hydrocephalus. Specifically, gait velocity (evaluated with a 10-meter timed gait) and cognition (evaluated with the Montreal Cognitive Assessment [MoCA]) were assessed preoperatively and postoperatively in 85 patients. Gait velocity improved from 0.9 m/s to 1.2 m/s, and MoCA scores improved from 24/30 to 26/30.

Therefore the most essential factor in selecting adult patients for ETV is the subtype of hydrocephalus itself. To date, the ETVSS has not been validated in the population of adults with hydrocephalus. One of the main challenges is the category “age,” as it adds 50 points automatically to an adult patient’s score, which accounts for over 50% of the total score. Also, a large percentage of young children were a part of the original study in which the ETVSS was derived and validated. Therefore use of this clinical prediction rule in adults is inappropriate and currently not recommended.

Endoscopic Third Ventriculostomy for Unrecognized Congenital Hydrocephalus

Unrecognized congenital hydrocephalus is a category of adult hydrocephalus with a congenital pattern, that was not treated before 18 years of age. The term late-onset idiopathic aqueductal stenosis (LIAS) has been used to refer to this category, but this is misleading. Even though having an aqueductal pattern is the most common etiology in this category, other causes such as idiopathic communicating hydrocephalus can be the cause. Aqueductal pattern refers to triventricular hydrocephalus (lateral and third ventricular dilatation) with complete or severe narrowing of the aqueduct. Hamilton and colleagues found that of 163 symptomatic adult hydrocephalus patients, the majority had an aqueductal pattern (69%) and made up the majority of the patients who underwent a primary ETV (70%).

Adult patients with aqueductal stenosis respond to ETV if adequately selected based on clinical presentation, radiologic findings of triventricular hydrocephalus, and minimal subarachnoid spaces. Success typically results in a complete or near-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 this subgroup is 50% to 86.5%, including several reports of success rates approximating 80% within 6 to 22 months of follow-up. ^, ^,

Endoscopic Third Ventriculostomy for Acquired Hydrocephalus (Usually Noncommunicating)

Secondary noncommunicating adult-onset hydrocephalus is defined as obstructive hydrocephalus resulting from a lesion impeding the CSF pathway. The first choice for treatment of such lesions is removal or partial resection of the lesion to reestablish CSF flow; however, in many cases this is not possible or warranted. In these cases ETV may be a feasible alternative. Pineal region tumors, tectal gliomas, and posterior fossa tumors are the most common types of mass lesions that cause secondary noncommunicating hydrocephalus in both adults and children. Rare entities such as thalamic masses, cerebellar infarctions, and neurocysticercosis are also described. ^, Hamilton and colleagues found that tumors were involved in 14% of 163 adult patients with hydrocephalus who underwent an ETV. Success rates for ETV to treat patients with tectal gliomas have been reported to be 81% to 88%, although 18% of these patients may require a second ETV for ostomy blockage. ^, Diaz and colleagues reviewed 14 patients who had obstructive hydrocephalus due to a tectal glioma and who underwent ETV. At follow-up (median, 3.9 years), 13 of the 14 patients remained shunt independent. It should be noted that none of the patients underwent endoscopic biopsy of the lesion. Tectal gliomas are uncommon and, in general, represent only about 4% of all cases treated with ETV, both pediatric and adult. Arachnoid cysts, especially those found in the suprasellar region, prepontine region, third ventricle, or posterior fossa, can often cause obstructive hydrocephalus. Dusick and associates found that ETV was successful in treating hydrocephalus secondary to these arachnoid cysts in 86% of cases.

ETVs for tectal and pineal region masses are sometimes paired with an endoscopic biopsy of the lesion through the third ventricle. Despite a high rate of success with the ETV itself, diagnostic rates for the masses are generally lower (69%–90%). Complications associated with biopsy are documented at a rate of approximately 18%. ^, Common complications of these types of biopsy include intracerebellar and IVHs, upgaze palsies, ventriculitis, and sodium balance disturbances. ^,

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