COMMENTARY Commentary: A Cohort Comparison Analysis of Fixed Pressure Ventriculoperitoneal Shunt Valves With Programmable Valves for Hydrocephalus Following Nontraumatic Subarachnoid Hemorrhage Christoph Wipplinger, MD * Christoph J. Griessenauer, MD ‡§ ∗ Department of Neurosurgery, Medical University of Innsbruck, Innsbruck, Austria; ‡ Department of Neurosurgery and Neuroscience Institute, Geisinger, Danville, Pennsylvania; § Research Insti- tute of Neurointervention, Paracelsus Medical University, Salzburg, Austria Correspondence: Christoph J. Griessenauer, MD, Department of Neurosurgery, 100 N Academy Ave, Danville, PA 17822, USA. Email: christoph.griessenauer@gmail.com Received, June 3, 2019. Accepted, June 8, 2019. Published Online, November 20, 2019. Copyright C  2019 by the Congress of Neurological Surgeons T he authors present a retrospective cohort study comparing ventriculoperitoneal shunts (VPS) with adjustable and fixed pressure (differential pressure) valves for nontraumatic subarachnoid hemorrhage (SAH)-associated hydrocephalus. 1 To date, few studies have compared adjustable to nonad- justable VPS valves in this setting. Therefore, the present study is a welcome addition to the current literature. Shunt-dependent hydrocephalus is a common complication of SAH and occurs in 20% to 30% of patients. 2 - 4 Risk factors include acute hydro- cephalus, high Fisher grade, intraventricular hemorrhage, high Hunt and Hess grade, and old age. 5 Transient hydrocephalus can be treated with external ventricular drainage, persistent cases, however, require permanent cerebrospinal fluid (CSF) diversion. The etiology of SAH- associated hydrocephalus is not entirely under- stood. Only sparse evidence supports the notion that posthemorrhagic hydrocephalus is a result of obstruction and malabsorption. 6 A recent study by Karimy et al 7 demonstrated that blood metabolites from intraventricular hemorrhage are causing inflammation and subsequent hyper- secretion in the choroid plexus. While there is clear evidence in favor of VPS placement in general, the choice of the pressure valve remains controversial. 4 With fixed pressure valves, the required drainage pressure has to be estimated based on the anticipated amount of shunt drainage necessary to maintain normal intracranial pressure and ventricular size at the time of implantation. If an adjustment has to be made, this can only be achieved by reoperation and shunt valve replacement. With adjustable pressure valves, however, the amount of CSF can be modified transcutaneously in an outpa- tient setting using a magnet if more or less drainage is required. Especially in posthemor- rhagic hydrocephalus, adjustments in the early follow-up period are frequently needed as several studies have shown that the optimal pressure tends to change over time. 8 , 9 While more expensive, adjustable pressure valves theoretically require fewer revision surgeries for overdrainage or underdrainage justi- fying the upfront cost increase. 8 , 10 However, certain adjustable valves may change their setting in an magnetic resonance imaging (MRI) scanner requiring a shunt check after MRI. And certain types of adjustable valves may also require skull x-rays to evaluate the degree of adjustment. This may be a potential factor for additional cost that is frequently not taken into account. 11 In the present study, the authors reported an overall VPS revision rate of 19.7% (n = 13). Among those, 9.1% (n = 3) occurred in the adjustable valve group and 30.3% (n = 10) in the fixed pressure group, which was statistically significant. Overdrainage occurred in 3 patients in the adjustable valve group and in 2 patients in the fixed valve group, while 1 patient in each group had underdrainage. All patients with overdrainage or underdrainage in the adjustable pressure valve group were managed with valve adjustments, while all patients in the fixed pressure group required revision surgery. Other reasons for VPS revision included infection, obstruction, and misplacement. The decision on the type of valve was made on an individual basis by the treating physician. Patients requiring replacement of their external ventricular drain due to obstruction received more adjustable pressure valves. As acknowledged by the authors, 1 a major limitation of this study is the large difference in follow-up time between groups. Patients with adjustable pressure valves had average follow-up of 5.4 mo, while patients with fixed pressure valves were followed for an average of 24.9 mo. The conclusion that adjustable valves required fewer revisions might therefore be subject to bias E102 | VOLUME 18 | NUMBER 4 | APRIL 2020 www.operativeneurosurgery-online.com Downloaded from https://academic.oup.com/ons/article-abstract/18/4/E102/5634050 by guest on 26 May 2020