Cerebrospinal with adult

Journal ofNeurology, Neurosurgery, and Psychiatry 1995;58:715-723

Cerebrospinal fluid shunt dynamics inpatients with idiopathic adult hydrocephalussyndrome

Jan Malm, Bo Kristensen, Markku Fagerlund, Lars-Owe Koskinen, Jan Ekstedt

AbstractThe objective was to assess CSF dynam-ics of different shunt constructions inpatients with adult hydrocephalus syn-drome and correlate these findings toclinical outcome, neuroradiology, andthe specifications of the shunts providedby the manufacturer. Thirty four patientswith idiopathic adult hydrocephalus (nor-mal pressure hydrocephalus) syndromewere included in a prospective, consecu-tive case series. A differential pressurevalve (Cordis Hakim standard system) wasused in 28 patients and a variable resis-tance valve (Cordis Orbis-Sigma) in six.A constant pressure infusion method

was used; CSF pressure and conductancewere determined before surgery. Threemonths after shunt placement CSF pres-sure, the "pressure v flow" curve, andgravity induced flow were measured.There was no difference between mean

preoperative and postoperative restingCSF pressures in patients with Hakimshunts. The opening pressures of theHakim shunts were higher than the valueproposed by the manufacturer. A pro-nounced gravity effect induced CSF flowand decrease of the CSF pressure. Infunctioning variable resistance valves,CSF dynamics normalised postopera-tively. There was no gravity effect and thecharacteristic s shaped "pressure v flow"curve was sometimes seen. Six patients(three differential pressure valves, threevariable resistance valves) had non-func-tioning shunts. Four of these patientswere improved after the operation butimprovement was transient in three. Inall patients, there was no relationbetween the width of the ventricles andclinical improvement or CSF pressure.

In conclusion, the differential pressurevalve system does not behave accordingto the specifications provided by themanufacturer. A decrease in CSF pres-sure in patients with this shunt was solelydue to the effect of gravity. Eleven percent of the differential pressure valvesand 50% of the variable resistance valveswere non-functioning. In the functioningvariable resistance valves, the antisiphonsystem seems to be effective.

(C Neurol Neurosurg Psychiatry 1995;58:715-723)

Keywords: cerebrospinal fluid shunt; hydrocephalus;cerebrospinal fluid dynamics

Patients with the idiopathic adult hydro-cephalus syndrome (IAHS)1 2 are providedwith a shunt device to restore normal CSFdynamics and achieve a substantial functionalimprovement. Shunt failure, however, due toimproper placement, infection, obstruction,breakage, disconnection, or migration of theshunt is of major concern.3 The long termcharacteristics of the shunt may change."Shunt resistance and the corresponding CSFflow may vary according to the length and thediameter of the proximal and distal catheters.4Posture related changes may give a negativeintracranial pressure due to a gravity inducedflow (siphon effect) with secondary over-drainage,7-'0 hygroma, or subdural haematoma.The standard of CSF shunts may be

defined in terms of opening and closing pres-sure, antireflux properties, leakage, pressureand flow characteristics, mechanical dura-bility, and siphoning effect." 12 These vari-ables are determined in bench tests by themanufacturer before the operation but manyvalves have been found not to respondaccording to their specifications.F6

Shunt function cannot be assessed inpatients with IAHS by clinical examination orby pumping the valve." There is no criterionstandard for in vivo measurements of shuntfunction. Computed tomography, MRI,'1-6doppler ultrasonography,17 radionuclide stud-ies,'8-20 and thermography have been used tomeasure shunt flow in vivo. These methodsdo not take into consideration the importanceof pressure and flow characteristics of theshunt and the CSF system. With a CSFinfusion technique, it is possible to assesswhether CSF dynamics have been normalisedpostoperatively together with the properties ofthe shunt system, including the degree ofgravity induced CSF flow.We prospectively investigated 34 patients

with IAHS given ventriculoperitoneal shunts.Dynamics of CSF were evaluated preopera-tively and three months after the operationand compared with shunt characteristics pro-vided by the manufacturer, clinical response,pressure v flow curves, changes in CSFpressure, and gravity induced flow.

Materials and methodsPATIENTSThe study population consisted of 34 patients(25 men and nine women (mean age (SD)71-7 (5 1) years)) with IAHS.-'5 The diagno-sis was based on (a) a gait disturbance as apredominant and obligate symptom; (b) mental

Department ofNeurologyJ MalmB KristensenJ EkstedtDepartment ofRadiologyM FagerlundDepartment ofNeurosurgery,University Hospital ofNorthern Sweden,S-901 85 UmeA,SwedenL-O KoskinenCorrespondence to:Dr Jan Malm, Departmentof Neurology, UniversityHospital of NorthernSweden, S-901 85 UMEA,Sweden.Received 14 November1994 and in revised form18 January 1995Accepted 17 February 1995

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impairment, or urinary incontinence, or both(ranging from not clinically present to severedisturbances); (c) CT showing dilatation ofthe lateral ventricles without severe corticalatrophy; (d) absence of another disease thatmight explain the clinical symptoms or radio-logical findings. Informed consent for allaspects of the study was obtained from all thepatients.An extensive investigation was performed

in each patient to exclude other causes of gaitdisorder or dementia. The results of ancillaryinvestigations and clinical characteristics, andreasons for exclusion of patients are reportedelsewhere.29 Dynamic investigations of CSFand CT were performed in all patients beforesurgery and at three months after shunting.None of the patients had any symptoms orsigns of postoperative overdrainage. The CTdid not show any intracranial haematomas.All patients were investigated with the shuntpumping test,'3 but there was no evidence ofproximal or distal catheter obstruction.

SURGICAL METHODA variable resistance valve (Cordis Orbis-Sigma) was used in six patients. A differentialpressure valve (Cordis Hakim standard sys-tem; medium opening or closing pressure0-8-1-2 kPa) was used in 28 patients. Theshunt was introduced by a ventriculoperi-toneal approach. No shunt was revised duringthe study period.

from a continuously weighed bottle. The pres-sure in the bottle was regulated via an elec-tronic control system acting on the fluidwithin it by means of the air pressure from apump.The preoperative CSF pressure (Pcl) was

determined when the resting recording hadbeen stable for at least 10 minutes, usuallyafter 30-60 minutes of recording. The con-ductance of the CSF outflow pathways (Gop)was determined by applying different pressurelevels to the CSF space while recording theresulting inflow of artificial CSF into thepatient. Thus within a few minutes a stableflow at a stable pressure was obtained.Usually, three different pressure/flow valueswere aimed at. The volume accountingmethod was used to calculate the pressure/flow relation. The slope for the pressure/flowvalues is equal to the Gop.To avoid errors due to body position or

physical exercise, the investigation after opera-tion was started with the CSF infusion. Therewas no external pressure on the distal catheterof the shunt. The pressure/flow curve was anindicator of the amount of CSF eliminated viathe shunt because the quantity eliminatedthrough the natural pathways was knownfrom the preoperative Gop measurement (fig1). Usually three assessments were appropri-ate to determine the pressure/flow relation indifferential pressure shunts. The pressure/flow

DEFINITIONS AND UNITS OF MEASUREMENTSI units have been used. Because a variety ofunits are cited in the medical literature, thefollowing conversion factors are given:Pressure: 1 kPa = 102 mm H20 = 7-5 mm Hg.Conductance: 1 mm3.kPa-'.s-1 = 6 x 10-3 ml(cm H2O)'- .min- I = 8 x 10-3 (mm Hg)- 1.min- l.Resistance: the inverse of conductance.Flow: 1 mm3.s-' = 3-6 ml/h = 0-06 cm3 min-'The following abbreviations have been used:Pcl = CSF pressure preoperatively; Pc2 =CSF pressure postoperatively; Pc3 = CSFpressure postoperatively after sitting for 10minutes; ICP = intracranial pressure; HP =hydrostatic pressure (length of gravity effectedCSF column); OP = opening pressure of theshunt; PP = perfusion pressure of CSF (thedriving force of CSF flow between the ventri-cles and the abdomen); Gop = conductanceof CSF outflow; Q = CSF flow; R = resis-tance in the shunt system.

DYNAMIC STUDIES ON CSFThe CSF dynamic studies6 3032 were per-formed preoperatively and at three monthsafter operation. Briefly, at 0800, after 12hours of bed rest, two needles (outer diameter1-2 mm) were inserted in the L3-L4 inter-space. Free passage was assessed by aspirationof 2 ml CSF, which was replaced with artifi-cial CSF. The patient was then placed supinewith the zero pressure reference level at thecranial sagittal centre. Drainage of CSF andinfusion of artificial CSF was made to and

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Figure 1 How to read the figures. CSF pressure andpressure vflow characteristics preoperatively andpostoperatively.



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Shunt dynamics in cerebrospinalfluid in patients with idiopathic adult hydrocephalus syndrome

characteristics of the variable resistanceshunts are S shaped and multiple pressure/flow values were obtained. The opening pres-sure of the differential pressure shunts couldbe defined as the point where the pressure/flow curve started to increase steeply (fig 1).

After the CSF infusion test, the CSF pres-sure declined spontaneously. The postopera-tive CSF pressure (Pc2) was determinedwhen the resting recording had been stable forat least 10 minutes, usually after 30-60 min-utes of recording.The gravity (or siphoning) effect of the

shunt was tested at the end of the investiga-tion. Patients were in the sitting position for10 minutes, after which they were again laidsupine. The corresponding CSF pressure(Pc3) was registered using the same zero pres-sure reference level as above. In a healthy con-trol or a shunted patient without a gravityeffect, the Pc3 is the same as Pc2 (fig 2A). In ashunted patient with a gravity effect, Pc3should be lower than Pc2 (fig 2B).

ASSESSMENT OF SHUNT FUNCTIONFour variables were estimated for each shunt:(1) The difference between the CSF pressurepreoperatively and postoperatively (Pci - Pc2).(2) The difference between the preoperativeCSF pressure and the postoperative CSFpressure after sitting for 10 minutes (Pcl -Pc3). (3) The gravity effect (Pc2 - Pc3). (4)

Figure 2 The CSFpressure recording before,during, and after sittingfor10 minutes in a patientwithout a shunt (A) andin a patient with a shunt(B).

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Table 1 Preoperative (Pcl) and postoperative (Pc2 and Pc3) mean values ofCSFpressures in patients with Hakim and Orbis-Sigma shunts

Valve system n Mean (95% CI) (kPa) P value

CSF pressure,preoperative (PcI) Hakim 28 1 9 (1-7-2-1)

Orbis-Sigma 6 2-3 (1-7-2-9)CSF pressure,

postoperative (Pc2) Hakim 28 1 9 (1-7-2-1)Orbis-Sigma 6 1-7 (1-2-2-2)

Difference(Pcl- Pc2) Hakim 28 0 0 (- 01 to 0-1) NS

Orbis-Sigma 6 0-6 (0-01-2) NSCSF pressure,

postoperative (Pc3) Hakin 28 1-3 (1-2-1-4)Orbis-Sigma 6 1-6 (10-02-2)

Difference(Pci - Pc3) Hakim 28 0-6 (0 4-0-8) < 0-0001

Orbis-Sigma 6 0 7 (0-1-4) NSDifference (gravity effect)

(Pc2 - Pc3) Hakim 28 0-6 (0-5-07) < 0-0001Orbis-Sigma 6 0-1 (- 0-2 to 0 4) NS

The preoperative pressure v flow curve (theconductance) compared with the postopera-tive pressure v flow curve of the shunt.A shift > the 95% confidence interval

(95% CI) on the differences between the CSFpressures was taken as an indicator of alter-ation.

VARIABLES OF SURGICAL OUTCOMEThe subject was asked to walk 25 metres asfast as possible. The task was repeated threetimes and the mean gait velocity (m/s) wascalculated. The gait was videotaped. The pre-operative recording was compared with therecording at three months after operation.The recordings were rated as same, better, orworse by two physiotherapists independentlyon the six items: gait initiation, rhythmicmovements, step size, shuffling, wide base,and turning."334 If at least four items wererated as better, the video recording wasclassified as improved. The between raterreliability was high (Spearman rank correla-tion r2 = 0-96). The gait was classified asmarkedly improved if the video recording wasimproved and the postoperative gait velocitywas > 25% faster.The mini mental state examination

(MMSE)3" was performed by one of the neu-rologists. A shift >i the 95% CI was taken asindicator of improvement.

NEURORADIOLOGYAll measurements on CT were done by asenior neuroradiologist without knowledge ofthe patients' CSF dynamics. The width of thethird ventricle was measured in mm and thelateral ventricles measured as a ventricularindex.36

STATISTICAL METHODSStatistical analyses were conducted with theJMP program for the Macintosh computer.'7Comparisons of variables before and afteroperation were evaluated by a paired t test;95% CIs were calculated. Linear regressionanalyses or analyses of variance (ANOVA)were performed when appropriate.

ResultsDIFFERENTIAL PRESSURE VALVE (CORDISHAKIM STANDARD SYSTEM)Table 1 shows the mean values of Pcl, Pc2,and Pc3. There were no differences betweenthe preoperative and postoperative pressures(Pcl - Pc2). There was a significant gravityeffect.

Considering that the main objective ofshunting patients with IAHS is to decreaseCSF pressure, four types of responses couldbe seen: (1) (fig 3A; 11 patients): thedecrease of Pcl - Pc2 was > upper 95% CI,which indicates a pronounced reduction inCSF pressure postoperatively. In six of thepatients, Pc3 was < 1-0 kPa. There was aprominent gravity effect (Pc2 - Pc3) and thepressure v flow curves showed increasing flowwith increasing pressure, well above the CSFdrainage preoperatively. Patient 10 had a very

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high conductance preoperatively and theshunt did not improve the pressure flowresponse despite a high differential valve pres-sure. Gait was not improved in four patientsand MMSE was not improved in five. (2) (fig3B; eight patients): the Pcl - Pc3 decreasedbetween the upper and lower 95% CI andPcI - Pc2 was unchanged. The gravity effectand pressure v flow curves show that therewas a flow through the shunt. In three of thepatients, Pc3 was < 1 kPa. Gait was notimproved in two patients and MMSE was notimproved in four. (3) (fig 3C; six patients):Pcl - Pc3 was unchanged or slightlydecreased postoperatively and Pcl - Pc2 wasincreased. This indicates that there was nodecrease in the preoperative CSF pressure,even after the patient has been sitting in thepostoperative assessment. As shown by the

gravity effect and the pressure v flow curvesthe shunts were functioning. In one of thepatients, Pc3 was below 1 kPa. Gait improvedin all patients whereas MMSE deteriorated or

was unchanged in three patients. (4) (fig 3D;three patients): Pcl - Pc3 was unchanged or

slightly increased and Pci - Pc2 was

increased. This indicates that there was no

postoperative change in CSF pressure com-pared with the preoperative registrations. Theshunts in these patients were not functioningas the gravity effect was absent and the pres-sure v flow curves indicated CSF drainageonly via the natural pathways.

VARIABLE RESISTANCE VALVE (CORDISORBIS-SIGMA) SYSTEMTable 1 shows the mean values of Pcl, Pc2,and Pc3. There was a tendency towards

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Table 2 Width of the ventri'cles preoperatively and postoperativelyPreoperati've Postoperative DifferenceMean (95o CI,) Mean (950o GI) Mean (950o CI P value

Ventricularindex 0-33 (0-31-0-35) 0-31 (0-29-0-33) 0-026 (0-016-0-036) < 00001

Third ventricle(mm) 13-7 (12-7-14-7) 12-7 (11-6-13-8) 1-000 (0-480-1-520) < 0001

reduction in the mean CSF pressure post-operatively (Pc 1 - Pc3). There was no gravityeffect (Pc2 - Pc3).

Figure 4 shows the results for the sixpatients. In patients 29-32 the CSF pressuresdecreased postoperatively. There was no grav-ity effect. The sigma shaped correlationbetween pressure v flow described by themanufacturer occurred in patients 30 and 31.In patient 32 the pressure v flow curve wassimilar to the preoperative drainage of CSF bynatural pathways.

In patients 33 and 34, there was no reduc-tion in CSF pressure postoperatively and nogravity effect. The S shaped pressure v flowcurve was seen, but the flow was about thesame as preoperatively despite high differen-tial valve pressures. These shunts were notfunctioning.

OVERALL CLINICAL OUTCOME RELATED TOSHUNT FUNCTIONSix patients' shunts (patients 26, 27, 28, 32,33, 34; figs 3D and 4) were not functioningaccording to the CSF dynamic tests. Despitethis, four of the patients were improved afterthe operation. In the 28 patients with func-tioning shunts, gait was markedly improved in1 1, slightly improved in 10, and unchanged inseven. According to the MMSE, 13 patientsimproved >t the upper 95% CI (two points),12 were unchanged, and three deteriorated.The relation between clinical improvement

and PcI, Pc2, and Pc3 was assessed. The Pc2was positively related to improvement inMMSE (linear regression r2= 0-38; P =

0-0005). The Pc2 tended to be higher inpatients with a marked improvement of gait(ANOVA P = 0-07).

WIDTH OF THE VIENTRICLESSize of the lateral and third ventriclesdecreased significantly postoperatively (table2). Nine patients had a pronounced reductionin the ventricular index (>e upper 95% CI).According to the CSF dynamics, seven ofthese shunts were functioning (patients 5, 6,13, 14, 20, 21, 30) and two non-functioning(patients 32, 33). Seven patients had nochange or an increased width of the lateralventricles postoperatively. All of these hadfunctioning shunts according to the CSFdynamics (patients 3, 8, 10, 11., 16, 19, 22).There were no correlations between the sizeof the ventricles and Pci1, Pc2, or Pc3. Norwas there any correlation between improve-ment in gait or MMSE and the indices of theventricles.

DiscussionThere is a pressing need for a criterionstandard for assessing the function of CSFshunts. In bench tests, CSF infusion methodsare the natural choice.411233 In our opin-ion, a similar method should be used inshunted patients. Measurements of resis-tance40 4' or intracranial pressure in relation tobody position9 as indicators of shunt functionhave been used. A systematic investigation ofa homogeneous patient population preopera-tively and postoperatively, however, withrespect to CSF dynamics, shunt function andoutcome of surgery has never been made. Thepurpose of the preoperative CSF dynamicinvestigation was to assess CSF pressure and

Figure 4 CSF dynamicsof Orbis Sigma shuntsbefore and after operation.Forfurther explanationssee the materials andmethods section.

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conductance. In our experience, the conduc-tance does not predict the outcome ofsurgery, although it is reduced in patientswith IAHS.'9 It is unlikely that a patientwith IAHS with a high conductance (lowresistance) would be improved by a shunt(patient 10).The purpose of a shunt is to facilitate the

CSF outflow and lower the CSF pressure.The dynamics of CSF shunts suggests that the

Figure 5 Schematic drawing ofshunt dynamics. Thecranial sagittal centre is the zero pressure reference level.The peritoneal pressure is presumed to be zero. (A)Equilibrium in the supine position. CSFformation is equalto CSF absorption and the hydrostatic pressure is zero.The opening pressure wiU balance the CSF pressure. Thereis no perfusion pressure and no net CSFflow. (B)Standing up. The hydrostatic pressure is added to theintracranial pressure (minus the opening pressure of theshunt). There is a net CSFflow because of the resultingperfusion pressure. There will be aflow through the shuntuntil the perfusion pressure is zero. (C) Equilibrium in thestanding position. Because ofCSFflow, the intracranialpressure decreases or even becomes negative. The perfusionpressure declines and when it reaches zero CSFflow isminimised. (D) Constant pressure infusion method.During the CSF infusion test, the patient is supine. Thehydrostatic pressure is zero and the peritoneal pressure ispresumably the same. The perfusion pressure is settled bythe CSF pressure (which could be altered by lumbar CSFinfusion) and the opening pressure of the shunt. Multiplepressurelflow levels can be obtained. ICP = intracranialpressure; HP = hydrostatic pressure; OP = opening orclosing pressure of the shunt; PP = perfusion pressure ofCSF (the drivingforce of CSF); AP = abdominalpressure; Q = CSFflow; R = resistance in the shuntsystem.

postoperative CSF pressure (Pc2) shouldnever exceed the opening pressure of theshunt (fig 5A). According to the manufac-turer's specifications, the opening pressure ofa medium differential pressure valve shouldbe 1 2 kPa; however, Pc2 went below 1-5 kPain just one patient (5) and the preoperativeand postoperative mean CSF pressures(Pcl - Pc2) did not differ. Figure 3A showsthe patients in whom the opening pressure ofthe shunt was below the preoperative CSFpressure (Pcl) but exceeded 1-2 kPa. In theremaining patients with a functioning shuntthe opening pressure exceeded or was equal toPcl and explains why Pc2 remainedunchanged (fig 3B). A considerable betweenpatient variation in postoperative CSF pres-sures (Pc2) was seen in patients with differen-tial pressure shunts, though similar shuntdevices had been implanted. In patients withfunctioning variable resistance shunts(patients 29-31), there was a more markeddecline in CSF pressure compared with thedifferential pressure shunts (table 1). The Pc2was below 1-5 kPa in all patients.

Drainage of CSF through the shunt at dif-ferent pressures as well as the opening pres-sure of the shunt can be determined when aconstant pressure infusion method is used. Ifthere is no drainage through the shunt, thepressure flow curve is flat and similar to thepreoperative conductance. As the openingpressure is exceeded, the flow increases lin-early with pressure. Despite the aforemen-tioned variations of opening pressure indifferential pressure shunts, most had a linearpressure flow relation according to their speci-fications (fig 3A-C) when opening pressurewas exceeded. The corresponding curve of thevariable resistance valve should consist ofthree intervals of differential pressures, eachgiving different amounts of CSF drainage. Wecould only confirm a similar pattern in threeof six patients (fig 4; patients 30, 31, 33).Recently, the construction of the variableresistance valve (Cordis Orbis-Sigma) shunthas been criticised.5

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When patients are standing, CSF flows inthe tubing between the ventricles and theabdominal cavity because of an increasedhydrostatic pressure (fig 5B). After an intervalof disequilibrium, the flow is counterbalancedby the differential pressure of the valve and adecreased or even negative intracranial pres-sure (fig 5G). The siphoning effect is mostoften considered as an unwanted consequenceof the shunting, resulting in adverse events. Inthe present study, a gravity induced flow wasseen in most of the differential pressure valvesbut never in a variable resistance valve. Thegravity induced flow was of fundamentalimportance in lowering the CSF pressure(Pci - Pc3; table 1) in most patients withdifferential pressure shunts. No adverseevents were caused by a low CSF pressure(Pc3 < 1 kPa) in the first three months.The Pc2 increased in some patients with

differential pressure valves (fig 3C). This maybe explained by a gravity induced flow. Mostpatients are upright for most of the day andthe siphoning effect will prevent drainagethrough the natural outflow pathways. Thiscould leave the arachnoidal villi in an off stateduring the supine position at night and cause afurther reduction in conductance.

Six patients in the present study had non-functioning shunts (figs 3D and 4). Despitethis, four of these six had an improved gaitand two had improved MMSE scores. Theimprovement in gait was transient in three ofthese patients. It is known that non-shuntedpatients with IAHS may improve weeks ormonths after a CSF tap. 44243 Temporaryimprovement after shunt implantation hasbeen outlined.44 The rationale may be that theshunt dysfunction comes near to the CSFdynamic investigation. Gait and MMSEscores failed to improve in patients with func-tioning shunts (patients 10, 16, 17, 29), prob-ably because of irreversible brain damage.Decrease in ventricle width is often taken asevidence of shunt function. The presentstudy, however, showed no relation betweenwidth of ventricles, shunt function, or clinicalimprovement.

Ascertainment of differential pressure valve(Cordis Hakim standard system) function bythe CSF infusion technique clearly showedthat the valve system in vivo did not behaveaccording to the specifications provided bythe manufacturer. In terms of gravity effectand the pressure flow curves, a CSF flow and adecrease in CSF pressure is achieved at leastin the upright position and apparently sufficesto ameliorate the clinical symptoms to someextent in most of the patients. Shunt failurewas common in the variable resistance valve(Cordis Orbis-Sigma). The properties of thefunctioning shunts seem to be satisfactory.

We thank Lars-Johan Liedholm, Lars Forsgren, HakanFriden, and Goran Eriksson for helpful discussion and com-ments on the text of this article. The study was supported byKarl-Oskar Hansson's foundation, the Swedish Society of theNeurologically Disabled (NH.R), and Norrliandsfonden.

1 Adams R, Fisher C, Hakim S, Ojemann R, Sweet W.Symptomatic occult hydrocephalus with "normal"cerebrospinal-fluid pressure. N Engl J Med 1965;273:117-26.

2 Hakim S, Adams R. The special clinical problem of symp-tomatic hydrocephalus with normal cerebrospinal fluidpressure. JNeurol Sci 1965;2:307-27.

3 Sainte-Rose C, Piatt JH, Renier D, et al. Mechanical com-plications in shunts. Pediatr Neurosurg 1991;17:2-9.

4 Aschoff A. In-vitro-Testung von Hydrocephalus-Ventilen.Thesis. Heidelberg: University of Heidelberg 1994.

5 Trost HA, Heissler HE, Claussen G, Gaab MR. Testingthe hydrocephalus shunt valve: long-term bench testresults of various new and explanted valves. The needfor a model for testing valves under physiological condi-tions. EurJ Pediatr Surg 199 1;1(suppl 1):38-40.

6 Ekstedt J, Friden H. Hydrodynamic properties of CSFshunt systems. In: Shulman K, Marmarou A, Miller JD,Becker DP, eds. Intracranial Pressure IV. Berlin:Springer-Verlag, 1980:483-8.

7 Chapman PH, Cosman ER, Arnold MA. The relationshipbetween ventricular fluid pressure and body position innormal subjects and subjects with shunts: a telemetricstudy. Neurosurgery 1990;26: 181-9.

8 Foltz EL, Blanks JP. Symptomatic low intracranial pres-sure in shunted hydrocephalus. J Neurosurg 1988;68:401-8.

9 Fox JL, McCullough DC, Green RC. Effect of cere-brospinal fluid shunts on intracranial pressure and oncerebrospinal fluid dynamics. J Neurol NeurosurgPsychiatry 1973;36:302-12.

10 Pudenz RH, Foltz EL. Hydrocephalus: overdrainage byventricular shunts. A review and recommendations. SurgNeurol 1991;35:200-12.

11 International Organization for Standardization. New workingdocument on neurosurgical implants-sterile, single-usehydrocephalus shunts and components. Pforzheim: DINGermany, 1992.

12 American Society for Testing and Materials. Standardpractice for evaluating and specifying implantable shuntassemblies for neurosurgical application. In: AnnualBook ofASTM Standards. New York: American NationalStandards Institute, 1989:647-79.

13 Piatt JJ. Physical examination of patients with cere-brospinal fluid shunts: is there useful information inpumping the shunt? Pediatrics 1992;89:470-3.

14 Martin AJ, Drake JM, Lemire C, Henkelman RM.Cerebrospinal fluid shunts: flow measurements with MRimaging. Radiology 1989;173:243-7.

15 Frank E, Buonocore M, Hein L. Magnetic resonanceimaging analysis of extremely slow flow in a model shuntsystem. Childs Nerv Syst 1992;8:73-5.

16 Savader SJ, Savader BL, Murtagh FR, Clarke LP, SilbigerML. MR evaluation of flow in a ventricular shunt phan-tom with in vivo correlation. J Comput Assist Tomogr1988;12:765-9.

17 Chadduck WM, Crabtree HM, Blankenship JB, AdametzJ. Transcranial Doppler ultrasonography for the evalua-tion of shunt malfunction in pediatric patients. ChildsNerv Syst 1991;7:27-30.

18 Borbely K, Simkovics M, Paraicz E, Pasztor E.Scintigraphic study of cerebrospinal fluid shunts. ActaNeurochir (Wien) 1989;100:115-9.

19 Howman-Giles R, McLaughlin A, Johnston I, Whittle I. Aradionucleotide method of evaluating shunt functionand CSF circulation in hydrocephalus. J Neurosurg1984;61:604-5.

20 Reilly PL, Savage JP, Doecke L. Isotope transport studiesand shunt pressure measurements as a guide to shuntfunction. BrJ Neurosurg 1989:3;681-90.

21 Vanneste J, Augustijn P, Tan WF, Dirven C. Shuntingnormal pressure hydrocephalus: the predictive value ofcombined clinical and CT data. J Neurol NeurosurgPsychiatry 1993;56:252-6.

22 Greenberg J, Shenkin H, Adams R. Idiopathic normalpressure hydrocephalus-a report of 73 patients.J Neurol Neurosurg Psychiatry 1977;40:336-41.

23 B0rgesen S, Gjerris F. The predictive value of conduc-tance to outflow of CSF in normal pressure hydro-cephalus. Brain 1982;105:65-86.

24 Fisher CM. Hydrocephalus as a cause of disturbances ofgait in the elderly. Neurology 1982;32:1358-63.

25 Petersen R. Surgical treatment of idiopathic hydrocephalusin elderly patients. Neurology 1985;35:307-1 1.

26 Vassilouthis J. The syndrome of normal-pressure hydro-cephalus. J Neurosurg 1984;61:501-9.

27 Laws ER, Mokri B. Occult hydrocephalus: results ofshunting correlated with diagnostic tests. Clin Neurosurg1977;24:316-33.

28 Black P, Ojemann R, Tzouras A. CSF shunts for demen-tia, incontinence and gait disturbance. Clin Neurosurg1985;32:632-5 1.

29 MaIm J, Kristensen B, Karlsson T, Fagerlund M,Elfverson J, Ekstedt J. The predictive value of CSFhydrodynamic tests in patients with the idiopathic adulthydrocephalus syndrome. Arch Neurol 1995 (in press).

30 Ekstedt J, CSF hydrodynamic studies in man. 1. Methodof constant pressure CSF infusion. J Neurol NeurosurgPsychiatry 1977;40:105-19.

31 Ekstedt J, Friden H. Estimation of CSF outflow resistancein humans: infusion methods. In: Gjerris F, B0rgesenS, Soelberg S0rensen P, eds. Outflow of cerebrospinalfluid. Copenhagen: Alfred Benzon foundation, 1989:148-66.



j.com/

J Neurol N


ownloaded from



32 Kristensen B, Malm J, Markgren P, Ekstedt J. CSF hydro-dynamics in superior sagittal sinus thrombosis. J7 NeurolNeurosurg Psychiatry 1992;55:287-93.

33 Nutt JG, Marsden CD, Thompson PD. Human walkingand higher-level gait disorders, particularly in theelderly. Neurology 1993;43:268-79.

34 Graff-Radford NR, Godersky JC. Normal-pressure hydro-cephalus. Onset of gait abnormality before dementiapredicts good surgical outcome. Arch Neurol 1986;43:940-2.

35 Folstein MF, Folstein SE, McHugh PR. Mini-mentalstate: a practical method for grading the cognitive statusof patients for clinicians. J7 Psychiatr Res 1976;12:189-98.

36 Hanson J, Levander B, Liliequist B. Size of the intracerebralventricles as measured with computer tomography,encephalography and echoventriculography. Acta Radiol1978;suppl 346:98-106.

37 Sall J, Ng K, Hecht M. JMP. Cary: SAS Institute Inc,1991.

38 Sainte-Rose C, Hooven MD, Hirsch J-F. A new approach

in the treatment of hydrocephalus. Neurosurg 1987;66:213-26.

39 Watts C, Keith HD. Testing the hydrocephalus shuntvalve. Childs Brain 1983;10:217-28.

40 Czosnyka M, Maksymowicz W, Batorski L, Koszewski W,Czosnyka Z. Comparison between classic-differentialand automatic shunt functioning on the basis of infusiontest. Acta Neurochir (Wien) 1990;106:1-8.

41 Costabile G, Probst C. Intrathecal infusion tests anddecrease in shunt revisions and infections. Neurochirurgia1988;31:134-5.

42 Fisher CM. Communicating hydrocephalus. Lancet 1978;7:37.

43 Wikkelso C, Andersson H, Blomstrand C, Lindqvist G.The clinical effect of lumbar puncture in normal pres-sure hydrocephalus. Neurol Neurosurg Psychiatry 1982;45:64-9.

44 Vanneste J, Augustijn P, Dirven C, Tan WF, GoedhartZD. Shunting normal-pressure hydrocephalus: do thebenefits outweigh the risks? A multicenter study andliterature review. Neurology 1992;42:54-9.



j.com/

J Neurol N


ownloaded from


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