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J Neurosurg 99:52–57, 2003

Treatment of hydrocephalus determined by the European Orbis Sigma Valve II survey: a multicenter prospective 5-year shunt survival study in children and adults in whom a flow-regulating shunt was used PATRICK W. HANLO, M.D., PH.D., GIUSEPPE CINALLI, M.D., W. PETER VANDERTOP, M.D., PH.D., JOOP A. J. FABER, PH.D., LARS BØGESKOV, M.D., SVEND E. BØRGESEN, M.D., PH.D., JÜRGEN BOSCHERT, M.D., PAUL CHUMAS, M.D., F.R.C.S.(SN), HANS EDER, M.D., PH.D., IAN K. POPLE, M.D., F.R.C.S., WILLY SERLO, M.D., PH.D., AND ECKEHARD VITZTHUM, M.D., PH.D. Department of Neurosurgery, Utrecht University Medical Center, and Center for Biostatistics, Utrecht University, Ultrecht, The Netherlands; Department of Pediatric Neurosurgery, Santobono Children’s Hospital, Naples, Italy; Department of Neurosurgery, Vrije Universiteit University Medical Center, Amsterdam, The Netherlands; University Clinic of Neurosurgery, Neuroscience Center, Rigshospitalet, Copenhagen, Denmark; Department of Neurosurgery, University Hospital Mannheim, Germany; Department of Neurosurgery, Leeds General Infirmary, Leeds, United Kingdom; Department of Neurosurgery, Karl-Franzens University, Graz, Austria; Department of Neurosurgery, Frenchay Hospital, Bristol, United Kingdom; Division of Paediatric Surgery, Oulu University Hospital, Oulu, Finland; and Neurosurgical Clinic, University of Leipzig, Germany Object. The goal of this study was to evaluate the long-term results of a flow-regulating shunt (Orbis Sigma Valve [OSV] II Smart Valve System; Integra NeuroSciences, Sophia Antipolis, France) in the treatment of hydrocephalus, whether it was a first insertion procedure or surgical revision of another type of shunt, in everyday clinical practice in a multicenter prospective study. Methods. Patients of any age who had hydrocephalus underwent implantation of an OSV II system. The primary end point of the study was defined as any shunt-related surgery. The secondary end point was a mechanical complication (shunt obstruction, overdrainage, catheter misplacement, migration, or disconnection) or infection. The overall 5-year shunt survival rates and survival as it applied to different patient subgroups were assessed. Five hundred fifty-seven patients (48% of whom were adults and 52% of whom were children) were selected for OSV II shunt implantation; 196 patients reached the primary end point. Shunt obstruction occurred in 75 patients (13.5%), overdrainage in 10 patients (1.8%), and infection in 46 patients (8.2%). The probability of having experienced a shunt failure– free interval at 1 year was 71% and at 2 years it was 67%; thereafter the probability remained quite stable in following years (62% at the 5-year follow-up examination). No difference in shunt survival was observed between the overall pediatric ( 16 years of age) and adult populations. In the pediatric age group, however, there was a significantly lower rate of shunt survival in children younger than 6 months of age (55% at the 5-year follow-up examination). Conclusions. In this prospective study the authors demonstrate the effectiveness of flow regulation in the treatment of hydrocephalus both in children and in adults. Flow-regulating shunts limit the incidence of overdrainage and shunt-related complications. The overall 5-year shunt survival rate (62%) compares favorably with rates cited in other recently published series.

KEY WORDS • hydrocephalus • cerebrospinal fluid shunt system • shunt survival • flow regulation YDROCEPHALUS is one of the most common conditions encountered in neurosurgical practice. Progress in its management has been substantial, but appropriate treatment is still far from ideal. Since the first implantation of a CSF shunt, approximately 50 years ago by Nulsen,31 various shunts and shunt components have been developed in an attempt to provide continuous, failure-free, CSF diversion for patients with hydrocephalus.

H

Abbreviations used in this paper: CI = confidence interval; CSF = cerebrospinal fluid; DP = differential pressure; OSV = Orbis Sigma Valve; REM = rapid eye movement.

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Previous investigations have shown that the probability of a 1-year survival of CSF shunts is as high as 60%.8,34,40 By far the most frequent cause of shunt failure is mechanical complication.3,6,7,14,15,17,19,28,30,34,38,44 Despite many modifications to original shunt-valve designs, improvements in treatment results have been limited.10 Shunt malfunctions have various causes related to the shunt itself, the surgical technique, or specific patient characteristics. Among those, chronic overdrainage caused by excessive variations in DP induced by gravitational effects and vasogenic activities (for example, REM sleep), has been demonstrated to be an important factor responsible J. Neurosurg. / Volume 99 / July, 2003

Treatment of hydrocephalus for poor long-term results.1,4,35,37,39 Both symptomatic and asymptomatic overdrainage are seen just as frequently in adults as in children.8 Because of this, the original model of the OSV was designed to limit CSF flow through the valve by progressively narrowing the orifice with increasing pressure, as a pressure-sensitive ring moves along a variable-diameter rod.39 Unlike other devices, such as antisiphon and gravity-compensating mechanisms, which at best only limit postural overdrainage or siphoning, flow-regulating mechanisms address both postural and vasogenic overdrainage (caused by REM sleep, physical exertion, coughing, and so forth). In a prospective randomized trial in which three types of valves (conventional DP valves, a valve with an antisiphon device [Delta valve], and a flow-regulating system [OSV]) were compared, it was shown that none of these devices was able to lower the rate of shunt malfunction by 50% at the 1-year follow-up examination (a difference of 50% being the design hypothesis of the study).8 One potential weakness of the OSV shunt system was the severe flow restriction within the valve, making it more sensitive to valve obstruction by small particles of debris.4 In an attempt to overcome this problem and also to minimize the size of the valve, several technical improvements were made by the manufacturer in the development of the OSV II Smart Valve System (Integra Neurosciences, Sophia Antipolis, France). The purpose of this multicenter prospective study was to investigate the 5-year rate of shunt survival for this modified flow-regulating system (OSV II) both in adults and in children. Clinical Material and Methods Patient Population All patients with hydrocephalus referred to the surgeons involved in the study at each center were selected for OSV II shunt implantation and included in the study. Clinical presentation of hydrocephalus reflected symptoms of increased intracranial pressure or increasing head circumference. The cause of the hydrocephalus, sex and age of the patient at implantation, and imaging data were separately recorded for each patient included in the study. All these data were recorded, regardless of whether the OSV II shunt implantation was an initial implantation procedure or surgical revision of another shunt system. The sizes of the ventricles on computerized tomography or magnetic resonance images at implantation were classified as slit, normal, slightly enlarged, moderately enlarged, or extremely enlarged. The study complied with the principles stated in the Declaration of Helsinki of the World Medical Association (1989). All nine participating centers were familiar with implanting the OSV II shunt system. Patient exclusion criteria included previous OSV II shunt implantation, CSF seeding of tumor cells, and expected patient survival shorter than 1 year. Treatment of Hydrocephalus

Regardless of the cause of the hydrocephalus, shunts were implanted according to the common neurosurgical clinical practice of each participating center. Because no J. Neurosurg. / Volume 99 / July, 2003

specified surgical protocol was mandatory during the study, surgeons were free to use their own implantation techniques and to choose any configuration of OSV II shunt system available on the market (one-, two-, or three-piece system, with or without antechamber; ventriculoatrial or ventriculoperitoneal shunt). The prophylactic use of antibiotic agents was recorded. Follow-Up Review

The total follow-up period was set at 5 years. Postoperative assessments, including neurological examination and accumulation of imaging data, were conducted at 1 week, 3 months, and yearly for 5 years after shunt insertion. The sizes of the ventricles were assigned scores at each followup visit. Patients presenting with a possible shunt dysfunction underwent appropriate diagnostic tests. The primary and secondary end points were recorded. Outcome Events

The primary end point of the study for each patient was defined as any shunt-related operation, which was performed for either a mechanical malfunction or infection. The secondary end points (mechanical complications) were further subdivided into the following: 1) shunt obstruction (proximal, distal or valve obstruction); 2) catheter malposition (misplacement, migration, or disconnection); and 3) shunt failure (due to underdrainage or overdrainage). Infection of the system was considered to be a shunt failure. Statistical Analysis

Kaplan–Meier survival analysis was used to assess overall 5-year shunt survival and survival in the different patient subgroups. The time to shunt failure was compared among the different subgroups by using log-rank tests to compare the equality of survival distributions. Baseline variables and secondary outcomes were evaluated using descriptive statistics and a multivariate Cox regression analysis. Results Patient Characteristics

During a 2-year period (October 1, 1996–September 30, 1998), 557 patients were included in the study. There was an equal distribution between female (267) and male patients (290), and between children (51.5% of patients) and adults (48.5% of patients). The mean patient age at shunt implantation was 27.4 years (range 0–84.1 years), with 95 patients (17%) younger than 6 months of age. The baseline characteristics of the patients are presented in Table 1. One third of the patients shared the diagnosis of congenital hydrocephalus and 65% had an acquired form of hydrocephalus. The most common causes of hydrocephalus included hemorrhage and spinal dysraphia (together accounting for 37.9%) and tumor (17.2%), with 9.3% of cases having an unknown cause (Table 2). Size of the Ventricles

Two thirds of the patients received an OSV II shunt as an initial implant. One third of the patients previously had received an alternative shunt and were assigned to the revision group. 53

P. W. Hanlo, et al. TABLE 1 Characteristics of patients with hydrocephalus Characteristic

No. of Patients (%)

all patients female male children ( 16 yrs) young infants (
6 mos) adults ( 16 yrs) true end points mechanical dysfunction infection deaths*

557 (100) 267 (47.9) 290 (52.1) 287 (51.5) 95 (17.1) 270 (48.5) 196 (35.2) 150 (26.9) 46 (8.3) 50 (9.0)

* No deaths were related to shunts.

Among patients in the initial implant group, prior to insertion of the OSV II shunt, moderate enlargement of the ventricles was the most frequent finding (67.7%), followed by slight enlargement (14.4%) and extreme enlargement (14.4%). After shunt implantation symptomatic overdrainage with slit ventricles occurred in 1.9% of patients at the 5-year follow-up review. In the revision group, before insertion of the OSV II shunt, moderate enlargement of the ventricles was the most frequent finding (47.2%), followed by slight enlargement (24.5%) and extreme enlargement (9.2%). After shunt implantation symptomatic overdrainage with slit ventricles occurred in 1.6% of patients as of the 5-year follow-up examination. Slit ventricles were identified in 3.1% of all patients in the revision group as a result of overdrainage caused by a previously implanted alternative shunt. At the 3-month follow-up examination, approximately 60% of patients were found to have more normally sized ventricles. This percentage of normalization remained stable over the following years. Surgical Aspects

The surgical technique used at each center was not modified for the study. In 96.1% of cases, a ventriculoperitoneal shunt was used and in 3.1% a ventriculoatrial shunt was implanted. The two-piece system (ventricular catheter separate from the valve) was used most frequently (83.8% of cases), followed by the one-piece system (13.5% of cases) and the three-piece system (1.6% of cases). At all centers prophylactic antibiotic agents were administered during the

TABLE 2 Causes of hydrocephalus in 557 patients

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Cause

No. of Patients (%)

infection hemorrhage spinal dysraphia other malformation trauma tumor chronic hydrocephalus other unknown missing data

35 (6.3) 152 (27.3) 59 (10.6) 54 (9.7) 32 (5.7) 96 (17.2) 40 (7.2) 30 (5.4) 52 (9.3) 7 (1.3)

TABLE 3 Mechanical complications associated with necessary shunt revision No. of Patients (%) Complication

All Patients

all complications ventricular catheter occlusion misplacement or migration disconnection distal catheter occlusion misplacement or migration disconnection valve obstruction valve hydrodynamics overdrainage undefined

150

270 Adults

287 Children

67

83

28 (5.0) 13 (2.3) 3 (0.5)

15 (5.6) 2 (0.7) 1 (0.4)

13 (4.5) 11 (3.8) 2 (0.7)

11 (2.0) 5 (0.9) 2 (0.4) 36 (6.5) 28 (5.0) 10 (1.8) 14 (2.5)

6 (2.2) 3 (1.1) 1 (0.4) 12 (4.4) 13 (4.8) 9 (3.3) 5 (1.9)

5 (1.7) 2 (0.7) 1 (0.4) 24 (8.4) 15 (5.2) 1 (0.4) 9 (3.1)

operation; at some centers this treatment was continued for 24 hours postoperatively. There was no statistically significant difference regarding the complication rate and shunt survival among the nine centers involved (data not shown). Shunt Failure

During the follow-up period of the study, 196 patients (35.2%) reached the primary end point (any shunt-related surgery). Mechanical failure was observed in 26.9% of patients (76.5% of all end points). Proximal shunt occlusion occurred in 5%, distal occlusion in 2%, valve obstruction in 6.5%, and symptomatic overdrainage in 1.8%. Catheter (ventricular or distal) misplacement or migration and disconnection occurred in 4.1%. The different categories of mechanical complications are represented in Table 3. Infection produced shunt failure in 8.3% of the total population (23.5% of all end points) and in 9.8% of patients younger than 6 months of age. Fifty patients (9%) died during the course of the study, but there were no shunt-related deaths. The probability of a shunt failure–free interval for the total study population was 71% at 1 year and 67% at 2 years; thereafter the probability remained stable, with shunt survival demonstrated in 62% of patients (95% CI 60–64%) at the 5-year follow-up examination (Fig. 1). There was a significant difference in the rate of shunt survival between patients younger than 6 months of age and those older than 6 months of age (55 and 63%, respectively; log rank test: p = 0.05). It is interesting to note that this difference occurred with in the first few months following surgery. There was no statistical difference in survival between children ( 16 years of age) and adults. Specifically, complications due to overdrainage observed in these two groups did not differ significantly. The overall rate of shunt survival in the initial implant group was not statistically different from that in the revision group (65 and 56%, respectively), although mechanical complications occurred more often in the revision group (35.3%) than in the initial implant group (23.4%). Regarding the cause of the hydrocephalus (infection, hemorrhage, dysraphia, trauma, tumor, chronic hydrocephalus, or idiopathic cause), there was no significant differJ. Neurosurg. / Volume 99 / July, 2003

Treatment of hydrocephalus ence in shunt survival. Other variables (patient age at implantation, presence or absence of an antechamber, and one-piece or multipiece system) were evaluated using a Cox regression analysis. Only patient age younger than 6 months at implantation demonstrated a significant impact on the occurrence of a shunt failure in the total study population. The size of the ventricles at the time of implantation of the OSV II shunt did not influence the survival rate of the shunt. Nevertheless, the group of patients with slit ventricles, known to be correlated with the occurrence of a delayed proximal obstruction, was too small for statistical assessment. Furthermore, no statistical difference in survival was identified when the size of the ventricle was adjusted according to whether the procedure was an initial or revised implantation. Discussion Despite constant efforts since the advent of shunt implantation in the 1950s, shunt failure rates have remained stable. A recent randomized trial focusing on a pediatric population8 has shown results very comparable to what were published 20 years ago.2 The causes of shunt malfunction can be defined as those related to the patient, those related to the surgery, and those related to the shunt. Among shunt-related problems, chronic overdrainage has been demonstrated to cause both acute (symptomatic subdural hematoma) and more delayed (proximal obstructions or slit-ventricle syndromes) shunt failure.9,10,18 Overdrainage is a general term that encompasses all phenomena that induce shunt flows well in excess of CSF production rates. Postural overdrainage or siphoning has long been recognized as a cause of shunt complications, and a number of devices have been designed to limit the effects of this phenomenon. Decq, et al.,5 noted that a mediumpressure DP valve can experience flows greater than 200 ml/hour, compared with the normal CSF production rate, which is approximately 20 ml/hour, leading to very low intracranial pressures. It is interesting to note, however, that the overdrainage phenomenon can be caused by a physiological vasogenic activity that rarely has been taken into account. For instance, during REM sleep ICP increases to 100% above its baseline value, increasing the DP applied across the valve.4,39 Most persons involved in shunt development during the last few decades have tried to address the problem associated with chronic overdrainage. Nevertheless, research has concentrated mainly on controlling the side effects of gravity (Table 4). In the original OSV shunt system (Cordis Implants SA, Biot, France), the concept of flow regulation was incorporated to avoid overdrainage when the patient assumes the upright position39 as well as overdrainage due to vasogenic activity (REM sleep, coughing, and so forth). In a further attempt to avoid shunt complications, the OSV was redesigned into the OSV II Smart Valve System. A longterm shunt survival study was then conducted to confirm the clinical efficacy of the new OSV II shunt design. We found an overall OSV II shunt survival in 62% of patients (95% CI 60–64%) at the 5-year follow-up examination. The present findings demonstrate that the OSV II shunt system considerably reduces the rate of complications related J. Neurosurg. / Volume 99 / July, 2003

FIG. 1. Graph demonstrating overall shunt survival at 5 years.

to overdrainage and to shunt obstruction, particularly any obstruction due to occlusion of the catheter (distal or proximal). The finding that slitlike ventricles caused by CSF overdrainage are strongly related to poor long-term outcome due to ventricular catheter blockage has opened a potential area for improvement in shunt survival.16,26,32,40,42,43 Apart from the Shunt Design Trial,8 only few studies have addressed prospective long-term effectiveness of shunts designed to avoid overdrainage.45 Like the Shunt Design Trial for pediatric hydrocephalus, which demonstrated no overdrainage complications in the OSV group,8,24 our OSV II study also demonstrates a similar favorable outcome regarding overdrainage and, in general, an overall improved long-term survival when one considers the 5-year survival rate.23 Moreover, the results of our study compare favorably with those of other studies that only addressed the results of first-implant programmable shunts, reporting a 53.1% survival rate at 5 years.45 Although asymptomatic slit ventricles may eventually cause an increased rate of complications due to proximal catheter blockage, the development of the slit-ventricle syndrome itself represents one of the most difficult treatment challenges in the management of hydrocephalus.11–13,20–22,25,29, 33,36,41,43 The results of this study suggest that implanting a flow-regulating device can reverse or avoid this pattern of overdrainage and associated complications. Shunt obstruction remains a challenging mechanical problem for all types of CSF shunts. The total obstruction rate in this study is relatively low compared with the Shunt Design Trial8 (13.5 compared with 31.4%). The valve obstruction rate of the OSV II shunt is slightly higher than that of other shunts (6.5 compared with 4.4%), probably because the high resistance offered by the valve in the phase of flow regulation could make clotting easier than in valves with on–off mechanisms. Much lower proximal and distal catheter occlusion rates have been observed with the OSV II shunt system (5 compared with 10.5% and 2 compared with 4.9%, respectively). Flow regulation, at least among children, seems to reduce proximal catheter occlusion. This suggests that proximal catheter obstruction is related to valve overdrainage problems. 55

P. W. Hanlo, et al. TABLE 4 Issues related to overdrainage control mechanisms* Type of Shunt System Externally Adjustable Opening Pressure

Issue

overdrainage control IVP while patient is standing mechanism

sensitivity to location under skin surgical implantation MRI & magnetic field hazard

Siphoning-Reducing Device

Gravity-Compensating Device

Flow-Regulating Mechanism

none (unless reprogrammed) depends on setting valve opening pressure is adjusted through magnetic coupling

gravity

gravity

gravity, vasogenic

positive

negative

closes w/ negative IVP, opens w/ positive IVP

no

yes

resistance added by weight of metal balls when patient is vertical, or fluid is diverted through narrow channel when patient is vertical no

physiologically negative variable resistance maintains flow at approximate rate of CSF production

implant depth & valve orientation for programming adjusts in strong magnetic fields

at level of foramen of Monro none

must be in line w/ vertical axis of the body limits of MRI safety

no none none

* IVP = intraventricular pressure; MRI = magnetic resonance imaging.

Infants younger than 6 months of age fared significantly worse than older children. The Shunt Design Trial failed to show any significant effect of age on shunt survival, probably because in that study the age inclusion limit had been set too high (2 years). In the present study the cutoff point was set at 6 months, and a significant difference in shunt survival among younger children was observed, as expected. The 8.3% overall infection rate (including both children and adults) in this study is within the range reported in other series.8,27 Conclusions This multicenter prospective shunt-survival study of a flow-regulating shunt (the OSV II Smart Valve System) shows an overall survival rate of 62% (95% CI 60–64%) at the 5-year follow-up examination, a rate that compares favorably with those cited in other shunt studies. Among the evaluated variables in the total study population, only patient age younger than 6 months was a factor that significantly influenced the occurrence of shunt failure. The results of this study suggest that a flow-regulating shunt reduces the incidence of acute overdrainage and shunt obstruction due to proximal catheter occlusion, resulting in a better long-term shunt survival. Nevertheless, this only addresses some complications associated with shunt surgery. The majority of these complications occurs within the first few months after surgery and seems to be only marginally affected by the hydrodynamic characteristics of the drainage systems. Acknowledgment We thank Novella Research (Utrecht, The Netherlands) for their continuous support to keep this extensive survey going.

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Disclaimer None of the authors has any financial interest in the OSV II Smart Valve System or in Integra Neurosciences. Appendix The following persons and centers participated in the European OSV II study: Ian K. Pople, M.D., F.R.C.S. (Bristol, UK); Lars Bøgeskov, M.D., and Svend E. Børgesen, M.D., Ph.D. (Copenhagen, Denmark); Rainer W. Oberbauer, M.D. (deceased), and Hans Eder, M.D., Ph.D. (Graz, Austria); Paul Chumas, M.D., F.R.C.S.(SN) (Leeds, UK); Eckehard Vitzthum, M.D. (Leipzig, Germany); Jürgen Boschert, M.D. (Mannheim, Germany); Willy Serlo, M.D., Ph.D. (Oulou, Finland); Christian Sainte-Rose, M.D., and Giuseppe Cinalli, M.D. (Paris, France); and Peter Vandertop, M.D., Ph.D., and Patrick Hanlo, M.D. (Utrecht, The Netherlands). References 1. Aschoff A, Kremer P, Benesch C, et al: Overdrainage and shunt technology. A critical comparison of programmable, hydrostatic and variable-resistance valves and flow-reducing devices. Childs Nerv Syst 11:193–202, 1995 2. Choux M: Shunt complications. Monogr Neural Sci 8:1–6, 1982 3. Collins P, Hockley AD, Woollam DHM: Surface ultrastructure of tissues occluding ventricular catheters. J Neurosurg 48:609–613, 1978 4. Czosnyka ZH, Czosnyka M, Richards HK, et al: Laboratory evaluation of the Phoenix CRx diamond valve. Neurosurgery 48: 689–694, 2001 5. Decq P, Barat JL, Duplessis E, et al: Shunt failure in adult hydrocephalus: flow-controlled shunt versus differential pressure shunts—a cooperative study in 289 patients. Surg Neurol 43: 333–339, 1995 6. Del Bigio MRD, Bruni JE: Reaction of rabbit lateral periventricular tissue to shunt tubing implants. J Neurosurg 64:932–940, 1986 7. Di Rocco C, Marchese E, Velardi F: A survey of the first complication of newly implanted CSF shunt devices for the treatment of nontumoral hydrocephalus. Cooperative survey of the 1991–

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29. McLaurin RL: Ventricular shunts: complications and results, in McLaurin RL, Schut L, Venes JL, et al (eds): Pediatric Neurosurgery: Surgery of the Developing Nervous System, ed 2. Philadelphia: WB Saunders, 1989, pp 219–229 (Reference unverified) 30. Noetzel MJ, Baker RP: Shunt fluid examination: risks and benefits in the evaluation of shunt malfunction and infection. J Neurosurg 61:328–332, 1984 31. Nulsen FE, Spitz EB: Treatment of hydrocephalus by direct shunt from ventricle to jugular vein. Surg Forum:399–403, 1952 32. Oberbauer RW: The significance of morphological details for developmental outcome in infantile hydrocephalus. Childs Nerv Syst 1:329–336, 1985 33. Oi S, Matsumoto S: Morphological findings of postshunt slit-ventricle in experimental canine hydrocephalus. Aspects of causative factors of isolated ventricles and slit-ventricle syndrome. Childs Nerv Syst 2:179–184, 1986 34. Piatt JH Jr, Carlson CV: A search for determinants of cerebrospinal fluid shunt survival: retrospective analysis of a 14-year institutional experience. Pediatr Neurosurg 19:233–242, 1993 35. Pollack IF, Albright AL, Adelson PD, et al: A randomized, controlled study of a programmable shunt valve versus a conventional valve for patients with hydrocephalus. Hakim-Medos Investigator Group. Neurosurgery 45:1399–1411, 1999 36. Rekate HL: Classification of slit-ventricle syndromes using intracranial pressure monitoring. Pediatr Neurosurg 19:15–20, 1993 37. Sainte-Rose C: Shunt obstruction: a preventable complication? Pediatr Neurosurg 19:156–164, 1993 38. Sainte-Rose C, Hoffman HJ, Hirsch JF: Shunt failure. Concepts Pediatr Neurosurg 9:7–20, 1989 39. Sainte-Rose C, Hooven MD, Hirsch JF: A new approach in the treatment of hydrocephalus. J Neurosurg 66:213–226, 1987 40. Sainte-Rose C, Piatt JH, Renier D, et al: Mechanical complications in shunts. Pediatr Neurosurg 17:2–9, 1991/92 41. Scott RM: Preventing and treating shunt complications, in Scott RM (ed): Hydrocephalus. Baltimore: Williams & Wilkins, 1990, pp 115–121 42. Serlo W, Saukkonen AL, Heikkinen E, et al: The incidence and management of the slit ventricle syndrome. Acta Neurochir 99: 113–116, 1989 43. Serlo W, Saukkonen AL, von Wendt L, et al: Incidence and management of the slit ventricle syndrome (SLVS), in Brock M, Banerji AK, Sambasivan M (eds): Modern Neurosurgery 2. Berlin: WFNS, 1991, pp 441–446 44. Vernet O, Campiche R, De Tribolet N: Long-term results after ventriculo-atrial shunting in children. Childs Nerv Syst 11: 176–179, 1995 45. Zemack G, Romner B: Seven years of clinical experience with the programmable Codman Hakim valve: a retrospective study of 583 patients. J Neurosurg 92:941–948, 2000 Manuscript received August 29, 2002. Accepted in final form March 28, 2003. Address reprint requests to: Patrick W. Hanlo, M.D., Ph.D., University Medical Center Utrecht, Wilhelmina’s Children’s Hospital, Home Mailbox KC.03.063.0, P.O. Box 85090, 3508 AB Utrecht, The Netherlands. email: [email protected].

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