The prognostic value of clinical characteristics and parameters of cerebrospinal fluid hydrodynamics in shunting for idiopathic normal pressure hydrocephalus.

BACKGROUND: It is difficult to predict which patients with symptoms and radiological signs of normal pressure hydrocephalus (NPH) will benefit from a shunting procedure and which patients will not. Risk of this procedure is also higher in patients with NPH than in the overall population of hydrocephalic patients. The aim of this study is to investigate which clinical characteristics, CT parameters and parameters of cerebrospinal fluid dynamics could predict improvement after shunting. METHODS: Eighty-three consecutive patients with symptoms and radiological signs of NPH were included in a prospective study. Parameters of the cerebrospinal fluid dynamics were measured by calculation of computerised data obtained by a constant-flow lumbar infusion test. Sixty-six patients considered candidates for surgery were treated with a medium-pressure Spitz-Holter valve; in seventeen patients a shunting procedure was not considered indicated. Clinical and radiological follow-up was performed for at least one year postoperatively. FINDINGS: The odds ratio, the sensitivity and specificity as well as the positive and negative predictive value of individual and combinations of measured parameters did not show a statistically significant relation to clinical improvement after shunting. CONCLUSIONS: We conclude that neither individual parameters nor combinations of measured parameters show any statistically significant relation to clinical improvement following shunting procedures in patients suspected of NPH. We suggest restricting the term normal pressure hydrocephalus to cases that improve after shunting and using the term normal pressure hydrocephalus syndrome for patients suspected of NPH and for patients not improving after implantation of a proven well-functioning shunt.

Analysis of hearing loss after shunt placement in patients with normal-pressure hydrocephalus.

OBJECT: Following shunt placement for treatment of normal-pressure hydrocephalus (NPH), several patients suffered hearing loss. The authors undertook a study to analyze this outcome. METHODS: Sixteen patients in whom NPH was diagnosed were treated by placement of a ventriculoperitoneal shunt. Their hearing was assessed pre- and postoperatively by using pure tone audiometry. Two thirds of the ears tested showed a postoperative hearing loss of more than 10 dB. Recovery of the hearing loss occurred 6 to 12 weeks after shunt placement in 75% of the ears examined. CONCLUSIONS: Although shunt insertion for treatment of NPH results in a decrease in hearing, most of the loss can be recovered.

Hydrostatic and hydrodynamic considerations in shunted normal pressure hydrocephalus.

Symptoms of overdrainage, a frequent complication following shunting procedures especially in patients with normal-pressure hydrocephalus (NPH), are presumed to be caused by siphoning: gravity-enhanced flow of cerebro spinal fluid (CSF) through shunts in upright position. A critical reappraisal of siphoning and overdrainage (OD) is presented considering the occurrence of subdural hygromas (SDH) encountered in a group of patients shunted for NPH. The patients participated in the multicentre Dutch NPH study: 101 NPH patients were randomised for treatment with shunts with low or medium-high working pressure. Treatment with shunts with low working pressure resulted in an increased incidence of SDH (iSDH). Current physiological concepts of overdrainage are discussed and criticised. A new theory is presented on the basis of general physiological considerations. The theoretical model proposed yields a revised explanation for the origin of extremely low ventricular pressure in the upright position found with overdrainage. The efficacy of siphoning-preventing shunts and subtemporal decompression is explored in the light of the proposed theory.

Does CSF outflow resistance predict the response to shunting in patients with normal pressure hydrocephalus?

The value of the measurements of CSF outflow resistance (Rcsf) relative to predicting outcome after shunting was studied. In a group of 101 patients with mainly idiopathic normal pressure hydrocephalus (NPH) Rcsf was obtained by lumbar constant flow infusion. Gait disturbance and dementia were quantified using an NPH scale (NPHS) and disability by the Modified Rankin scale (MRS). Patients were assessed before and at 1, 3, 6, 9 and 12 months after surgery. Outcome measures were differences between the preoperative and last NPHS and MRS scores. Improvement was defined as a change of > or = 15% in NPHS and > or = 1 grade in MRS. Intention-to-treat analysis of all patients at one year yielded improvement of 57% in NPHS and 59% in MRS. Efficacy analysis, excluding comorbidity unrelated to NPH, revealed positive predictive values of around 80% at Rcsf < 18, and between 90% and 100% at Rcsf > or = 18 mm Hg/ml/min. For Rcsf > or = 18, the likelihood ratios were also higher. We conclude that the best predictor of the response to shunting is an Rcsf > or = 18 mm Hg/ml/min. Since two-thirds of the patients with Rcsf < 18 showed improvement as well, these patients should not be denied shunting.

Dutch Normal-Pressure Hydrocephalus Study: randomized comparison of low- and medium-pressure shunts.

OBJECT: The goal of this prospective 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 randomized 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 grades. 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 grades 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.

Dutch normal-pressure hydrocephalus study: prediction of outcome after shunting by resistance to outflow of cerebrospinal fluid.

The authors examined whether measurement of resistance to outflow of cerebrospinal fluid (Rcsf) predicts outcome after shunting for patients with normal-pressure hydrocephalus (NPH). In four centers 101 patients (most of whom had idiopathic NPH) who fulfilled strict entry criteria underwent shunt placement irrespective of their level of Rcsf obtained by lumbar constant flow infusion. Gait disturbance and dementia were quantified by using an NPH scale and the patient's level of disability was assessed by using the modified Rankin scale (mRS). In addition the Modified Mini-Mental State Examination was performed. Patients were assessed prior to and 1, 3, 6, 9, and 12 months after surgery. Primary outcome measures were based on differences between the preoperative and last NPH scale scores and mRS grades. Improvement was defined as a change measuring at least 15% in the NPH scale score and at least one mRS grade. Intention-to-treat analysis of all patients at 1 year yielded improvement for 57% in NPH scale score and 59% in mRS grade. Efficacy analysis, excluding serious events and deaths that were unrelated to NPH, was performed for 95 patients. Improvement rose to 76% in NPH scale score and 69% in mRS grade. Six cut-off levels of Rcsf were related to improvement in NPH scale score using two-by-two tables. Positive predictive values were approximately 80% for an Rcsf of 10, 12, or 15 mm Hg/ml/minute, 92% for an Rcsf of 18 mm Hg/ml/minute, and 100% for an Rcsf of 24 mm Hg/ml/minute. Negative predictive values were low. More important was the highest likelihood ratio of 3.5 for an Rcsf of 18 mm Hg/ml/minute. Extensive comorbidity was a major prognostic factor. Measurement of Rcsf reliably predicts outcome if the limit for shunting is raised to 18 mm Hg/ml/minute. At lower Rcsf values the decision depends mainly on the extent to which clinical and computerized tomography findings are typical of NPH.

Monitoring cerebral oxygenation: experimental studies and preliminary clinical results of continuous monitoring of cerebrospinal fluid and brain tissue oxygen tension.

Cerebral ischaemia is considered to be the central mechanism leading to secondary brain damage in patients with severe head injury. It would therefore seem appropriate to monitor cerebral oxygenation in these patients. The possibilities of continuous monitoring of brain tissue and CSF oxygen tension as parameters for cerebral oxygenation were evaluated. In experimental studies the influence of changed oxygen offer and decreased cerebral perfusion pressure on CSF and brain tissue pO2 were investigated. Fast changes in CSF pO2 were observed in response to decreasing oxygen offer. Slower changes were noted in response to hypo- and hyperventilation. An autoregulatory mechanism regulating CSF pO2 is postulated. Reducing cerebral perfusion pressure decreased both brain tissue and CSF pO2, but in the reperfusion phase after complete ischaemia a dissociation occurred between brain tissue and CSF pO2, CSF pO2 being restored, but brain tissue pO2 remaining low or even decreasing further. From these studies it is concluded that both CSF pO2 and brain tissue pO2 reflect changes in cerebral oxygenation caused by changes in oxygen offer as well as by changes in cerebral blood flow. Brain tissue pO2 is also sensitive to oxygen demand from the tissue. Preliminary studies of continuous monitoring of brain tissue pO2 in patients with severe head injury are reported.

Fontanelle pressure monitoring in infants with the Rotterdam Teletransducer: a reliable technique.

Intracranial Pressure (ICP) monitoring is important in patients at risk for raised ICP. In infants non-invasive methods for measuring ICP are to be preferred, and hence Anterior Fontanelle Pressure (AFP) measurements have been employed. So far, techniques used were not reliable since application of a transducer to the fontanelle generally influences the recorded pressure value. For the purpose of non-ambiguous ICP recording the Rotterdam Teletransducer was fitted in a special light weight skill adaptor, provided with a special fixation frame. With this adaptor the transducer can be set and maintained at accurate depth in the fontanelle according to the pressure depth curve. The plateau in the pressure depth curve represents actual ICP. The development of this reliable and reproducible technique is discussed. The results of instantaneous and continuous monitoring of AFP in 70 children with- and without neurological diseases are presented.

The Rotterdam Teletransducer: state of the device.

The developments of a telemetric device for monitoring intracranial pressure, the Rotterdam Teletransducer, are described. The major problem in telemetric pressure sensing devices consists of diffusion of water into the transducer, resulting in unpredictable zero drift. Therefore, special attention was paid to bonding techniques for sealing the transducer. The results of improved epoxy sealing, active metal brazing and glass bonding are described. In vitro tests showed transducers sealed with epoxy resin to be stable for two months. Using the more complicated techniques of glass bonding and active metal brazing, hermetic seals could be achieved with stable transducers for over one year. In vivo functioning of the Rotterdam Teletransducer was tested in acute and chronic animal experiments. The in vivo results corresponded to those obtained in the in vitro experiments. Regression analysis between epidural and ventricular fluid pressure showed a one to one ratio. Results of clinical application of the device in 22 patients are described. Accurate depth setting of the transducer on the dura, according to the pressure depth curve, was shown to be essential. The device has also been used with success for non-invasive fontanelle pressure measurements in infants. The depth positioning of the transducer on the fontanelle according to a pressure depth curve is described.

Non-invasive intracranial pressure monitoring. A technique for reproducible fontanelle pressure measurements.

Anterior fontanelle pressure was measured in 14 infants. A technique is described for preforming reproducible measurements utilising the Rotterdam Teletransducer. One gradually increasing the dept of the transducer relative to the fontanelle a characteristic pressure depth curve is obtained. The importance of positioning the transducer according to the pressure depth curve is described.

Long-term intracranial pressure monitoring.

Continuous or intermittent measurement of intracranial pressure (ICP) is important in patients at risk for raised ICP. Indications exist for short- and long-term measurements. The various methods used for short-term monitoring are discussed with their relative advantages and disadvantages. For long-term measurements of ICP use of a completely implantable telemetric epidural pressure transducer is indicated. No such device is commercially available. We have developed an inexpensive passive telemetric transducer for this purpose. Results obtained up till now have demonstrated its reliability for measurements of two to three months duration. The life span of the device is limited by degrading of the epoxy utilized for sealing of the titanium pressure sensing part to the radiolucent ceramic cap of the transducer, causing leakage of water into the transducer and false low measurements. Because of these problems new hermetic sealing techniques were tested. Both active metal brazing and glass bonding yielded good results and hermetic sealing could be obtained. The metal to ceramic bonding presented is generally applicable within the design of implants. Besides the technical progress reported, the experience with clinical use in 12 patients is presented.

The Rotterdam teletransducer. A telemetric device for measuring epidural pressure.

A discussion on the clinical value of telemetric measurements of intracranial pressure is presented. The technical improvements of an earlier described implantable epidural transducer are reported. Furthermore, the results are given of an in vivo study in dogs of the relation between epidural pressure as measured by this device and ventricular fluid pressure for variable physiologic conditions. An evaluation of the implantation technique is included and a justification for the selection of the constituting materials is given. Clinical results obtained in a patient are illustrated.

Epidural pressure monitoring with the so-called Rotterdam transducer. Further in vivo results.

Results of measurements in vivo of intracranial pressure obtained with a new telemetric epidural pressure transducer are described. The relations of epidural pressure to ventricular fluid pressure are studied in acute experiments and found to be linear, but variable. The functioning of 18 transducers was studied over many months of implantation.

A directional quantifying Doppler system for measurement of transport velocity of blood.

A transcutaneous Doppler device has been developed that measures primarily the directional transport velocity of blood, averaged over the vessel diameter, irrespective of its flow in adjacent vessels. Directional information is obtained by high or low-pass filtering of frequency converted versions of the received Doppler signals, applying low-cost, sharp filters in a superheterodyne system. Upper and lower channel signals are quantified separately to average directional velocity. Linear results from in vitro measurements are obtained.

Telemetered epidural pressure.

An implantable transducer capable of telemetering epidural brain pressure during long periods of time is described. The transducer is constructed from conventionally available materials, and routine workshop techniques are used. The coplanarity principle has been applied while the described mounting clamp allows discrete positioning of the transducer relative to the brain. Basically, the transducer consists of a coil-capacitor circuit in which alterations of epidural pressure induce changes in capacity and, thus, the transducer's resonance frequency. An external electromagnetically coupled impedance-measuring device converts the resonance frequency to a pressure analogous voltage. In vitro tests showed that the transducer had good accuracy and reliability for a period of more than 1 month. An in vivo experiment with a cat showed that the measured epidural pressure was linearly related to ventricular fluid pressure.