***TASK*** the task is to summarize an input biomedical literature in six sentences 
    ***INPUT*** the input is a biomedical literature 
    ***OUTPUT*** the output is the summary of an input biomedical literature in six sentences 
    ***DOCUMENTATION*** 
    ***EXAMPLES*** 
    Input: OBJECTIVE Forty percent of st and ard cerebrospinal fluid shunts implanted for the treatment of pediatric hydrocephalus fail within the first year . Two new shunt valves design ed to limit excess flow , particularly in upright positions , were studied to compare treatment failure rates with those for st and ard differential-pressure valves . METHODS Three hundred-forty-four hydrocephalic children ( age , birth to 18 yr ) undergoing their first cerebrospinal fluid shunt insertion were r and omized at 12 North American or European pediatric neurosurgical centers . Patients received one of three valves , i.e. , a st and ard differential-pressure valve ; a Delta valve ( Medtronic PS Medical , Goleta , CA ) , which contains a siphon-control component design ed to reduce siphoning in upright positions ; or an Orbis-Sigma valve ( Cordis , Miami , FL ) , with a variable-resistance , flow-limiting component . Patients were monitored for a minimum of 1 year . Endpoints were defined as shunt failure result ing from shunt obstruction , overdrainage , loculations of the cerebral ventricles , or infection . Outcome events were assessed by blinded independent case review . RESULTS One hundred-fifty patients reached an endpoint ; shunt obstruction occurred in 108 ( 31.4 % ) , overdrainage in 12 ( 3.5 % ) , loculated ventricles in 2 ( 0.6 % ) , and infection in 28 ( 8.1 % ) . Sixty-one percent were shunt failure-free at 1 year and 47 % at 2 years , with a median shunt failure-free duration of 656 days . There was no difference in shunt failure-free duration among the three valves ( P = 0.24 ) . CONCLUSION Cerebrospinal fluid shunt failure , predominantly from shunt obstruction and infection , remains a persistent problem in pediatric hydrocephalus . Two new valve design s did not significantly affect shunt failure rates OBJECT The goal of this prospect i ve study was to compare outcome after placement of a low- or medium-pressure shunt in patients with normal-pressure hydrocephalus ( NPH ) . METHODS Ninety-six patients with NPH were r and omized to receive a low-pressure ventriculoperitoneal shunt ( LPV ; 40 + /- 10 mm H2O ) or medium high-pressure ventriculoperitoneal shunt ( MPV ; 100 + /- 10 mm H2O ) . The patients ' gait disturbance and dementia were quantified by applying an NPH scale , and their level of disability was evaluated by using the modified Rankin scale ( mRS ) . Patients were examined prior to and 1 , 3 , 6 , 9 , and 12 months after surgery . Primary outcome measures were determined by differences between preoperative and last NPH scale scores and mRS grade s. The LPV and MPV shunt groups were compared by calculating both the differences between mean improvements and the proportions of patients showing improvement . Intention-to-treat analysis of mRS grade s yielded a mean improvement of 1.27 + /- 1.41 for patients with LPV shunts and 0.68 + /- 1.58 for patients with MPV shunts ( p = 0.06 ) . Improvement was found in 74 % of patients with LPV shunts and in 53 % of patients with MPV shunts ( p = 0.06 ) and a marked-to-excellent improvement in 45 % of patients with LPV shunts and 28 % of patients with MPV shunts ( p = 0.12 ) . All outcome measures indicated trends in favor of the LPV shunt group , with only the dementia scale reaching significance . After exclusion of serious events and deaths unrelated to NPH , efficacy analysis showed the advantage of LPV shunts to be diminished . Reduction in ventricular size was also significantly greater for patients in the LPV shunt group ( p = 0.009 ) . Subdural effusions occurred in 71 % of patients with an LPV shunt and in 34 % with an MPV shunt ; however , their influence on patient outcome was limited . CONCLUSIONS Outcome was better for patients who had an LPV shunt than for those with an MPV shunt , although most differences were not statistically significant . The authors advise that patients with NPH be treated with an LPV shunt Does the opening pressure of hydrostatic shunts influence the clinical outcome for patients suffering from idiopathic normal-pressure hydrocephalus ( NPH ) ? Between September 1997 and January 2003 , 123 patients with idiopathic NPH were surgically treated by implanting a  hydrostatic shunt at the Departments of Neurosurgery of the Unfallkrankenhaus Berlin and the University Homburg/Saar . As part of a prospect i ve r and omized study , all patients were examined preoperatively , postoperatively , and 1 year after the intervention . Forty-three percent of the patients showed a very good outcome , 25 % good outcome , 20 % fair outcome , and 12 % poor outcome 1 year after the shunt implantation . Patients treated with an opening pressure rating of 50 mmH2O in the low-pressure stage of the gravitational valve showed a better outcome than those with an opening pressure of 100 or 130 mmH2O . According to present knowledge , hydrostatic shunts with an opening pressure of 50 mmH2O for the low-pressure stage are the best option for patients with idiopathic NPH . Due to the prompt switching function when the patient changes posture ( lying down , st and ing , sitting , slanting etc . ) , the Miethke gravity-assisted valve ( GAV ) is more suitable in such cases than the Miethke Dual-Switch valve ( DSV ) OBJECTIVE The supremacy of low-pressure valves ( LPV ) in the therapy of patients with idiopathic normal pressure hydrocephalus ( iNPH ) has been proven by the Dutch NPH study . The downside of LPVs is the high rate of overdrainage complications . In the meantime gravitational units have been developed with the objective of minimising overdrainage complications . Do these gravitational units allow the same favourable outcomes as in the Dutch NPH study without overdrainage complications ? The goal of this prospect i ve r and omised controlled multicentre trial is to compare the rate of overdrainage complications after shunt surgery with programmable valves with or without a gravitational unit . METHOD Patients suspected with iNPH with gait ataxia and one or two other symptoms of Hakim 's triad and enlarged ventricles on CT or MRI underwent a cerebrospinal fluid ( CSF ) infusion test , CSF tap test and /or continuous ICP measurement in seven experienced centres . If iNPH was diagnosed the patients were r and omised to receive a ventriculoperitoneal shunt with a programmable valve with or without a gravitational unit . The patients were followed up for 3 , 6 and 12 months after surgery . The primary hypothesis of the study was that programmable valves with gravitational units will reduce the rate of overdrainage from 25 % to 10 % . The outcome measured by iNPH-specific outcome scales ( Kiefer score , Black grading scale ) and the generic quality of life ( short form 12 , SF12 ) was defined as the secondary endpoint . To detect the hypothesised difference in the incidence of overdrainage with a type I error of 5 % and a type II error of 20 % , correcting for multiple testing and an anticipated drop-out rate of 10 % , we planned to enrol 250 patients . To ensure safety and efficacy we performed a planned interim analysis halfway . RESULTS The study design has been found to be effective with regard to the primary hypothesis . CONCLUSION The design of the SVASONA study was developed to be able to confirm the primary hypothesis . Thus , the method of the study should solve the dilemma of the Dutch NPH study by the r and omised comparison of LPVs with and without gravitational units BACKGROUND AND PURPOSE Normal pressure hydrocephalus ( NPH ) is considered to be a combination of altered CSF resorption and a reversible form of cerebral ischemia . The hypothesis tested in this study was that a reduction in venous compliance in the territory drained by the superior sagittal sinus ( SSS ) is associated with NPH and cerebral ischemia . METHODS This prospect i ve study involved 27 patients without evidence of hydrocephalus . This group was subdivided into those with normal MR findings and those with evidence of ischemia or atrophy . Ten patients with NPH then underwent MR flow quantification studies of the cerebral vessels . Five of these patients had the same studies performed after CSF drainage . Vascular compliance was measured in the SSS and straight sinus territory by use of MR flow quantification with net systolic pulse volume ( NSPV ) and arteriovenous delay ( AVD ) as markers . RESULTS Vascular compliance of patients with ischemia or atrophy was significantly higher than that of healthy subjects ( mean NSPV in the SSS , 417 microL and 274 microL , respectively ) . Patients with NPH showed lower compliance than that of the healthy subjects in the SSS ( mean NSPV , 212 microL and 274 microL , respectively ; mean AVD , 42 ms and 89 ms , respectively ) . After intervention , the  NPH  group showed compliance approximating the group with ischemia/atrophy . CONCLUSION Vascular compliance is significantly different in the brains of healthy subjects as compared with that in patients with ischemia/atrophy or NPH OBJECT Patients with idiopathic normal pressure hydrocephalus ( iNPH ) often present with impaired  gait  and cognition  together with ventricular enlargement and normal intracranial pressure . Many have vascular risk factors as well as periventricular and deep white matter changes on MR imaging . Abnormal CSF dynamics , that is , high resistance to outflow or improvement after CSF drainage , indicate good effects of shunt surgery . The authors examined whether the worst-case iNPH patients with extensive vascular white matter disease and normal CSF dynamics would benefit from shunt surgery . These patients also fulfilled the criteria for Binswanger disease . Therefore , a r and omized controlled double-blind study was performed . METHODS Fourteen consecutive patients fulfilling the above criteria were r and omized to receive either open or closed shunts . At 3 months after surgery , the patients with initially ligated shunts had their shunts opened . Clinical evaluation consisting of 7 quantitative psychometric and 6 continuous gait tests was performed preoperatively and 3 and 6 months after surgery . RESULTS Patients r and omized to receive open shunts had improved motor ( 30 % increase ) and psychometric ( 23 % increase ) scores 3 months after shunt placement . There were no significant changes between the 3- and 6-month follow-up in these same patients . Conversely , those with initially ligated shunts were unchanged during the first 3-month period , although they improved in both motor ( 28 % ) and cognitive ( 18 % ) functions following removal of the ligature . CONCLUSIONS Patients with enlarged ventricles , hydrocephalic symptoms , and extensive vascular white matter changes benefit from shunt surgery Background : A previously reported multicenter r and omized trial assessed whether 2 new shunt valve design s would reduce shunt failure rates compared to differential pressure valves . The study did not show a significant difference in the time to first shunt failure .  Patients entered the trial between October 1 , 1993 , and October 31 , 1995 . The primary results were based on the patients ’ status as of October 31 , 1996 ( a minimum follow-up of 1 year ) . This report describes the late complications based on the patients ’ most recent follow-up . Methods : Three hundred and forty-four hydrocephalic children at 12 North American and European centers were r and omized to 1 of 3 valves : a st and ard differential pressure valve ; a Delta valve ( PS Medical-Medtronic ) or a Sigma valve ( NMT Cordis ) . Patients were followed until their first shunt failure . Shunt failure was defined as shunt surgery for obstruction , overdrainage , loculation or infection . If the shunt did not fail , follow-up was continued until August 31 , 1999 . Results : One hundred and seventy-seven patients had shunt failure . Shunt obstruction occurred in 131 , overdrainage in 13 , loculated ventricles in 2 and infection in 29 . The overall shunt survival was 62 % at 1 year , 52 % at 2 years , 46 % at 3 years , 41 % at 4 years . The survival curves for the 3 valves were similar to those from the original trial and did not show a survival advantage for any particular valve . Conclusions : Prolonged follow-up to date does not alter the primary conclusions of the trial : there does not appear to be one valve that is clearly the best for the initial treatment of pediatric hydrocephalus Objectives : The aim of this study was to prospect ively study perioperative variables associated with revision after shunt surgery  for adult hydrocephalus . Methods : Two protocol s were design ed to prospect ively study perioperative risk factors during shunt insertion .  Over 10 years ( 1995–2004 ) , 450 adult ( age > 16 years ) patients with first time shunt implantations were studied . Patients who had been treated with endoscopic third ventriculostomy were excluded from the study . All shunts were design ated as meeting one of two end points : ( 1 ) shunt failure requiring revision within 6 months or ( 2 ) no shunt failure within 6 months .  Shunt revision  within 6 months postoperatively was considered to be related to the shunting procedure . Results : 85 shunt revisions were performed within 6 months after insertion . During the study period the revision rate declined from 21.1 % 
    Output:
    
There is no evidence from r and omised clinical trials indicates that flow-regulated and differential pressure-regulated shunt valves differ with regard to clinical outcome , shunt failure , or intervention risks .