Idiopathic normal pressure hydrocephalus: analysis of factors related to cerebrospinal fluid dynamics determining functional prognosis

Invasive Preoperative Investigations in Idiopathic Normal Pressure Hydrocephalus: A Comprehensive Review

Idiopathic normal pressure hydrocephalus (iNPH) is a neurological disorder characterized by the triad of gait disturbance, cognitive impairment, and urinary incontinence. The condition is diagnosed mainly in older adults and is associated with ventricular enlargement without an increase in cerebrospinal fluid pressure. The clinical assessment involves a detailed medical history, physical examination, and cognitive testing. Neuroimaging is an essential part of the diagnostic workup for iNPH. However, to determine the suitability of patients for shunt surgery, a range of invasive preoperative investigations are employed. This narrative review aims to provide a comprehensive analysis of the current literature on invasive preoperative investigations in iNPH, focusing primarily on the lumbar infusion test, cerebrospinal fluid drainage tests, and continuous intracranial pressure monitoring. The strengths and limitations of each method, as well as their potential impact on treatment outcomes, are discussed.

Comparison of Noninvasive Measurements of Intracranial with Tap Test Results in Patients with Idiopathic Normal Pressure Hydrocephalus

Background

Normal pressure hydrocephalus is a disease directly related to the change in intracranial compliance and consequent repercussions in the brain parenchyma. Invasive monitoring of such parameters proves to be reliable especially for prognosis in neurocritical patients; however, it is not applicable in an outpatient service setting. The present study describes the comparison between the tap test results and the parameters obtained with a non-invasive sensor for monitoring intracranial compliance in patients with suspected NPH.

Methods

Twenty-eight patients were evaluated before and after lumbar puncture of 50mL of CSF (the tap test), comprising clinical assessment, magnetic resonance imaging, physical therapy assessment using the Timed Up and Go test, Dynamic Gait Index, BERG test, neuropsychological assessment, and recording of non-invasive intracranial compliance data using the Brain4care^® device in three different positions (lying, sitting, and standing) for 5 min each. The tap test results were compared to the Time to Peak and P2/P1 ratio parameters obtained by the device.

Results

The group that had a positive Tap test result presented a median P2/P1 ratio greater than 1.0, suggesting a change in intracranial compliance. In addition, there was also a significant difference between patients with positive, negative, and inconclusive results, especially in the lying position.

Conclusion

A non-invasive intracranial compliance device when used with the patient lying down and standing up obtained parameters that suggest correspondence with the result of the tap test.

Lumbar-peritoneal shunt for idiopathic normal pressure hydrocephalus and secondary normal pressure hydrocephalus

Objectives:

Normal-pressure hydrocephalus is a clinical syndrome consisting of dilated cerebral ventricles with the clinical triad of gait disturbance, cognitive impairment and/or urinary dysfunction. Lumbar-peritoneal (LP) shunt could improve idiopathic normal pressure hydrocephalus (iNPH) while its effectiveness on secondary NPH (sNPH) is elusive. We compared the clinical results of the patients who received LP shunt surgery between iNPH and sNPH.

Materials and Methods:

We retrospectively analyzed the patients who received LP shunt surgery in a single center from January 1, 2017, to June 30, 2017. Patients selected for LP shunt placement had at least two of three cardinal symptoms of iNPH. The symptoms should persist for more than 3 months with compatible brain magnetic resonance imaging findings. All patients were followed up with iNPH grading scale (iNPHGS) and Modified Rankin Scale (MRS) for evaluation.

Results:

Thirty-three patients (23 male and 10 female patients) with mean age 76-year-old completed follow-up in this study, and 17 patients received lumbar drainage tests and intracranial pressure measurements. Both iNPH (n = 22) and sNPH (n = 11) groups did not have major complications such as infection, nerve root injury, or shunt failure. Both groups have significant improvement in iNPHGS and MRS. Interestingly, we found the correlation between both opening intracranial pressure and pressure gradient difference to the improvement percentage from LP shunt.

Conclusion:

The safety and effectiveness for sNPH patients who received LP shunt placement are equivalent to the iNPH patients. Lumbar drainage test provides prerequisite outcome prediction and should be considered to identify NPH patients planned to receive LP shunt.

Guidelines for Management of Idiopathic Normal Pressure Hydrocephalus (Third Edition): Endorsed by the Japanese Society of Normal Pressure Hydrocephalus

Among the various disorders that manifest with gait disturbance, cognitive impairment, and urinary incontinence in the elderly population, idiopathic normal pressure hydrocephalus (iNPH) is becoming of great importance. The first edition of these guidelines for management of iNPH was published in 2004, and the second edition in 2012, to provide a series of timely, evidence-based recommendations related to iNPH. Since the last edition, clinical awareness of iNPH has risen dramatically, and clinical and basic research efforts on iNPH have increased significantly. This third edition of the guidelines was made to share these ideas with the international community and to promote international research on iNPH. The revision of the guidelines was undertaken by a multidisciplinary expert working group of the Japanese Society of Normal Pressure Hydrocephalus in conjunction with the Japanese Ministry of Health, Labour and Welfare research project. This revision proposes a new classification for NPH. The category of iNPH is clearly distinguished from NPH with congenital/developmental and acquired etiologies. Additionally, the essential role of disproportionately enlarged subarachnoid-space hydrocephalus (DESH) in the imaging diagnosis and decision for further management of iNPH is discussed in this edition. We created an algorithm for diagnosis and decision for shunt management. Diagnosis by biomarkers that distinguish prognosis has been also initiated. Therefore, diagnosis and treatment of iNPH have entered a new phase. We hope that this third edition of the guidelines will help patients, their families, and healthcare professionals involved in treating iNPH.

Acute Presentation of Normal Pressure Hydrocephalus After Transcatheter Aortic Valve Implantation: A Novel Interaction Between the First and Third Circulations

BACKGROUND

Idiopathic normal pressure hydrocephalus (iNPH) negatively affects gait and cognition abilities and urine continence in the elderly. It is associated with systemic hypertension, although the exact pathophysiology is still unknown. A correlation to increased intracranial pulsatility and decreased compliance was suggested. Transcatheter aortic valve implantation (TAVI) is increasingly used in the treatment of severe AS. New-onset systemic hypertension affects some patients after TAVI.

OBJECTIVE

To identify any association between aortic valve replacement and the development of NPH.

METHODS

A cohort was created retrospectively of all patients who were evaluated for NPH with cerebrospinal fluid (CSF) tap test at a single institute during 2014-2019. Patients were reviewed for a past medical history of aortic valvular disease or aortic valve replacement.

RESULTS

A total of 242 patients underwent evaluations for NPH. Of these patients, 133 were considered to have iNPH. Six patients underwent aortic valve replacement before the initial symptoms of NPH: 1 surgical and 5 TAVI. The time from aortic valve replacement to the initial NPH symptoms was <6 months in 3 patients (as low as 1 month in 2 of them). Two patients had functional improvement after CSF tap test and proceeded to receive a shunt, 4 and 6 months after TAVI, respectively. Two patients developed hypertension after TAVI. Pulse pressure increased by >10 mm Hg in 3 patients after TAVI.

CONCLUSIONS

This is the first case series of symptomatic NPH after TAVI. In this unique subgroup, NPH symptoms can develop rapidly. Post-TAVI iNPH represents a novel interaction between the blood and CSF circulations.

The Prediction of Shunt Response in Idiopathic Normal-Pressure Hydrocephalus Based on Intracranial Pressure Monitoring and Lumbar Infusion

BACKGROUND

Intracranial pressure (ICP) monitoring and infusion studies have long been used in the preoperative workup of patients with suspected idiopathic normal-pressure hydrocephalus (iNPH). We have analysed the predictive values of different measures derived from both investigations, emphasising the differences between responders and nonresponders.

MATERIALS AND METHODS

ICP monitoring and lumbar infusion studies were routinely performed during a 6-year period. Shunting was proposed when the resistance to cerebrospinal fluid outflow (ROUT) >12 mmHg/ml/min and/or a minimum 15 % of slow waves were detected. The outcome was evaluated 6 months after surgery. Recorded data from ICP monitoring were mean pressure and pulse amplitude, the total percentage of slow waves and the presence of different types of slow waves following the classification proposed by Raftopoulos et al. Recorded data from lumbar infusion studies were mean values of pressure and pulse amplitude during three epochs (basal, early infusion and plateau), ROUT and the pulsatility response to the increase in mean pressure during the infusion. This response was quantified by two pulse amplitude indexes: the pulse amplitude index during the early infusion stage (A1) and the pulse amplitude index during the plateau stage (A2).

RESULTS

Thirty shunted patients were evaluated at the end of the follow-up and 23 (76.7 %) of them improved. Differences in the percentage of slow waves, ROUT and both pulsatility indexes were not statistically significant. The proportion of patients with great symmetrical waves and pulse amplitude during the early infusion stage were higher in responders (p < 0.05). The predictive analysis yielded the highest accuracy, with ROUT and A1 as a logical "OR" combination.

CONCLUSION

The combined use of ICP monitoring and lumbar infusion to forecast the response to shunting in patients with suspected iNPH did not improve the accuracy provided by any of them alone.

[Normal pressure hydrocephalus: prognostic value of height in patients treated with an identical shunt system]

INTRODUCTION

Normal pressure hydrocephalus (NPH) is a clinical entity frequently managed by means of a cerebrospinal fluid shunt. Hydrodynamic hypotheses consider hydrostatic pressure (as well as height) a very important variable for shunt system function. However, we did not find empirical studies supporting the influence of height on clinical response in the literature. Our objective was to study the prognostic value of height, as a variable related to hydrostatic pressure, when an identical shunt system is used.

MATERIAL AND METHOD

A prospective series of 61 idiopathic NPH cases was analyzed. All cases were shunted by means of a ventricle-peritoneal system with a 100mmH2O opening pressure valve. Anthropometric, clinical, radiological and pressure variables were registered, as well as delay for treatment, improvement and complications.

RESULTS

78.7% of cases improved after shunting. This group of patients was significantly taller (P=.005) than the group without response (median value 165cm versus 152cm). There was also a significant correlation between height and ventricular size decrease after the shunt.

CONCLUSIONS

In our series opening valve pressure was a constant (100mmHg) and we could consequently focus on the effect of hydrostatic pressure (height). Moreover, we found a positive predictive value for taller patients, probably because we had selected an opening pressure especially suitable for them. Current gravitational valve shunt systems also recommend considering patient height when customising the system. Our study empirically supports this idea.

Predictors of the disappearance of triad symptoms in patients with idiopathic normal pressure hydrocephalus after shunt surgery

We identified factors that predict the disappearance of the triad of symptoms (gait disturbance, cognitive impairment and urinary incontinence) of idiopathic normal pressure hydrocephalus (iNPH) following shunt surgery in this study. We classified 71 patients with iNPH into those whose objective symptoms disappeared (disappearance group) or remained (residual group), for each of the triad symptoms 12 months after shunt surgery. Logistic regression analyses were used to identify the predictors of the disappearance of symptoms among 10 variables before shunt surgery (e.g., age, sex, severity of symptoms, Evans index, cerebrospinal fluid (CSF) pressure, CSF stasis on computerized tomographic cisternography, regional cerebral blood flow on single photon emission computed tomography, three kinds of prior diseases). For each of the triad symptoms, mild symptoms before shunt surgery were predictors of the disappearance of the symptom. Young age was also a predictor of the disappearance of gait disturbance. When the analysis was conducted using subscores of the Mini Mental State Examination, a successful visuoconstruction subtest and an absence of hypertension were predictors of the disappearance of cognitive impairment. None of the neuroimaging examinations predicted the disappearance of symptoms after shunt surgery in this study.

Design and benchmark testing of a bicorporal pump for the treatment of normal-pressure hydrocephalus and idiopathic intracranial hypertension

OBJECT

Addressing overdrainage and its associated complications is still one of the greatest challenges for future shunt designs for normal-pressure hydrocephalus and idiopathic intracranial hypertension. Nevertheless, as evidenced by tap test procedures, a small amount of CSF drainage seems to be enough to relieve patients' symptoms in most cases and, therefore, in opposition to other types of hydrocephalus, continuous CSF drainage may not be absolutely warranted. In such a clinical scenario, intermittent controlled drainage of a small amount of CSF during specific periods of the day through a 2-system pump may provide several advantages over continuous drainage of current single-system shunts. The goal in this study was to design and test an innovative concept of a bicorporal pump composed of a 2-part system. The first component was designed to be implanted in the patient and act as a pump connected to standard catheter tubing. The second component was designed to be used as an external device outside of the body and function as a power supply and control system. Ultimately, flow will only occur when the system is powered by the external device.

METHODS

Testing and comparisons were performed to evaluate free fluid flow and the maximal flow after pumping in the standing and supine positions. After this, the authors compared the hydrodynamic effects of 2 different housing systems (2- and 3-in systems). An attenuation test was performed to show the effects of electromagnetic forces at progressively increasing distances. Finally, a biocompatibility report of the raw material used in the pilot design was completed.

RESULTS

In the supine position, the effect of pumping was observed to increase the volumetric flow at a rate similar to or higher than that yielded in the free-flow tests. In relation to the attenuation test, it was observed that the volume drops off fairly quickly as the air gap distance was increased until ultimately reaching zero, with approximately 15 mm between the 2 components. In relation to the testing force, the 2-in housing model showed a considerable increase in the required electromagnetic force over the 3-in housing.

CONCLUSIONS

The authors successfully designed and tested a new intermittent drainage system through a bicorporal shunt, which provides several advantages over current single-system continuous drainage pumps. According to the authors' benchmark results, the 3-in housing model seems to be a better choice as it requires less force from the external electromagnet control. Moreover, attenuation tests demonstrated that, for proper functioning, the gap distance between the external and implanted devices should not be greater than 15 mm. Such initial benchmark results confirm the feasibility of such innovative design and provide support for future testing of the system in in vivo animal models and in future clinical series.

The pulsating brain: A review of experimental and clinical studies of intracranial pulsatility

The maintenance of adequate blood flow to the brain is critical for normal brain function; cerebral blood flow, its regulation and the effect of alteration in this flow with disease have been studied extensively and are very well understood. This flow is not steady, however; the systolic increase in blood pressure over the cardiac cycle causes regular variations in blood flow into and throughout the brain that are synchronous with the heart beat. Because the brain is contained within the fixed skull, these pulsations in flow and pressure are in turn transferred into brain tissue and all of the fluids contained therein including cerebrospinal fluid. While intracranial pulsatility has not been a primary focus of the clinical community, considerable data have accrued over the last sixty years and new applications are emerging to this day. Investigators have found it a useful marker in certain diseases, particularly in hydrocephalus and traumatic brain injury where large changes in intracranial pressure and in the biomechanical properties of the brain can lead to significant changes in pressure and flow pulsatility. In this work, we review the history of intracranial pulsatility beginning with its discovery and early characterization, consider the specific technologies such as transcranial Doppler and phase contrast MRI used to assess various aspects of brain pulsations, and examine the experimental and clinical studies which have used pulsatility to better understand brain function in health and with disease.

A subspace decomposition approach toward recognizing valid pulsatile signals

Following recent studies, the automatic analysis of intracranial pressure (ICP) pulses appears to be a promising tool for the prediction of critical intracranial and cerebrovascular pathophysiological variations during the management of many neurological disorders. A pulse analysis framework has been recently developed to automatically extract morphological features of ICP pulses. The algorithm is capable of enhancing the quality of ICP signals, recognizing valid (not contaminated with noise or artifacts) ICP pulses and designating the locations of the three ICP sub-peaks in a pulse. This paper extends the algorithm by proposing a singular value decomposition (SVD) technique to replace the correlation-based approach originally utilized in recognizing valid ICP pulses. The validation of the proposed method is conducted on a large database of ICP signals built from 700 h of recordings from 67 neurosurgical patients. A comparative analysis of the valid ICP recognition using the proposed SVD technique and the correlation-based method demonstrates a significant improvement in terms of (1) accuracy (61.96% reduction in the false positive rate while keeping the true positive rate as high as 99.08%) and (2) computational time (91.14% less time consumption), all in favor of the proposed method. Finally, this SVD-based valid pulse recognition can be potentially applied to process pulsatile signals other than ICP because no proprietary ICP features are incorporated in the algorithm.

Shunt surgery effects on cerebrospinal fluid flow across the aqueduct of Sylvius in patients with communicating hydrocephalus

We aimed to visualize and quantify the flow of cerebrospinal fluid (CSF) across the aqueduct of Sylvius in patients with communicating hydrocephalus using phase contrast MRI, and to evaluate the effect of ventriculoperitoneal (VP) shunt surgery on flow. We investigated aqueductal CSF flow using cine cardiac-gated phase contrast MRI in 10 normal volunteers and 10 patients with communicating hydrocephalus (who underwent VP shunt surgery). For qualitative evaluation, we used an in-plane phase contrast sequence in the midsagittal plane. Quantitative through-plane measurements were performed in the axial plane perpendicular to the aqueduct. The aqueduct area ranged from 0.02 cm(2) to 0.27 cm(2) in the shunt group; and from 0.01 cm(2) to 0.04 cm(2) in the control group (p<0.05). Aqueductal stroke volume (mean, standard deviation SD) ranged from 1.9 microL to 33.17 microL (17.41 microL, 10.1132) in the control group; and from 5.63 microL to 256 microL (87.20 microL, 79.0383) in the study group. Post-operatively the aqueductal stroke volume reduced significantly, ranging from 0.60 microL to 48.77 microL (13.19 microL, 18.08) (p<0.05). Peak systolic velocity (PSV) values in the patients before shunt surgery ranged from -1.05 cm/s to -8.10 cm/s (-4.39cm/s, 2.7619) and peak diastolic velocities (PDV) ranged from 0.62 cm/s to 5.16 cm/s (3.33 cm/s, 1.4451). Post- shunt; PSV values ranged from -0.37 cm/s to -3.90 cm/s (1.78 cm/s, 1.5143) and PDV range was 0.32 cm/s to 4.43 cm/s (1.78 cm/s, 1.6782). The post-operative reduction in velocity was significant (p<0.05). Thus, the aqueductal CSF flow after VP shunt was similar to flow in healthy volunteers.

Guidelines for management of idiopathic normal pressure hydrocephalus

With the rapid aging of Japanese society, medical care of the elderly has become an important social issue. Among various disorders manifesting dementia, gait disturbance, and urinary incontinence in the elderly population, normal pressure hydrocephalus (NPH), especially of idiopathic type (iNPH), is becoming noteworthy. The Guidelines for management of iNPH in Japan are created in compliance with the evidence-based medicine methods and published in 2004. This English version is made to show the diagnosis and treatment of iNPH with reference to the socio-medical background in Japan and to promote the international research on iNPH. They propose three diagnostic levels; possible, probable, and definite. They indicate the diagnostic importance of high convexity tightness and dilated sylvian fissure with mild to moderate ventriculomegaly on coronal magnetic resonance imaging. The cerebrospinal fluid tap test is regarded as an important diagnostic test because of its simplicity to perform and high predictability of the shunt efficacy. The use of programmable valves at shunt surgeries is recommended. Flowcharts for diagnosis, preoperative assessment, and prevention for complications of shunt surgery are made to promote a wide use of them.

Validation of grading scale for evaluating symptoms of idiopathic normal-pressure hydrocephalus

BACKGROUND/AIMS

We developed an idiopathic normal-pressure hydrocephalus grading scale (iNPHGS) to classify a triad of disorders (cognitive impairment, gait disturbance and urinary disturbance) of iNPH with a wide range of severity. The purpose of this study was to assess the reliability and validity of this scale in 38 patients with iNPH.

RESULTS

The interrater reliability of this scale was high. The iNPHGS cognitive domain score significantly correlated with the cognitive test scores, including the Mini-Mental State Examination (MMSE), the gait domain score with the Up and Go Test and Gait Status Scale scores, and the urinary domain score with the International Consultation on Incontinence Questionnaire-Short Form (ICIQ-SF) score. The MMSE, Gait Status Scale and ICIQ-SF scores significantly improved in patients whose iNPHGS scores improved after CSF tapping but not in those whose iNPHGS scores did not improve after CSF tapping. Fourteen of the 38 patients received shunt operations. In these 14 patients, changes in the iNPHGS cognitive and urinary domains after CSF tapping were significantly associated with the changes after the shunt operation.

A mathematical model of survival in a newly inserted ventricular shunt

OBJECT

The object of this study was to mathematically model the prognosis of a newly inserted shunt in pediatric or adult patients with hydrocephalus.

METHODS

A structured search was performed of the English-language literature for case series reporting shunt failure, patient mortality, and shunt removal rates after shunt insertion. A metaanalytic model was constructed to pool data from multiple studies and to predict the outcome of a shunt after insertion. Separate models were used to predict shunt survival rates for children (patients < 17 years old) and adults.

RESULTS

Shunt survival rates in children and adults were calculated for 1 year (64.2 and 80.1%, respectively), 5 years (49.4 and 60.2%, respectively), and the median (4.9 and 7.3 years, respectively). The longer-term rates predicted by the model agree closely with those reported in the literature.

CONCLUSIONS

This model gives a comprehensive view of the fate of a shunt for hydrocephalus after insertion. The advantages of this model compared with Kaplan-Meier survival curves are discussed. The model used in this study may provide useful prognostic information and aid in the early evaluation of new shunt designs and techniques.

Have we made progress in preventing shunt failure? A critical analysis

OBJECT

The goal of this study was to determine whether failure rates of hydrocephalus shunts have fallen over the years as a result of experience or technical improvements.

METHODS

A structured search was performed of the English language literature for case series reporting failure rates after shunt insertion. A metaanalytic model was constructed to pool data from multiple studies and to analyze failure rates statistically for temporal trends. Separate models were used for children (< 17 years old) and adults.

RESULTS

In children, the shunt failure rate was 31.3% for the 1st year and 4.5% per year thereafter. There were no significant changes in either rate over time. Although 1st-year failure rates in adults have fallen slightly over time, late failure rates have risen.

CONCLUSIONS

Progress in preventing shunt failures has not been made over the last several decades. Any improvements made in shunt materials or insertion techniques have been overshadowed by biological and other factors.

Shunts in normal-pressure hydrocephalus: do we place too many or too few?

OBJECT

The average 65-year-old patient with moderate dementia can look forward to only 1.4 quality-adjusted life years (QALYs), that is, longevity times quality of life. Some of these patients suffer from normal-pressure hydrocephalus (NPH) and respond dramatically to shunt insertion. Currently, however, NPH cannot be diagnosed with certainty. The authors constructed a Markov decision analysis model to predict the outcome in patients with NPH treated with and without shunts.

METHODS

Transition probabilities and health utilities were obtained from a review of the literature. A sensitivity analysis and Monte Carlo simulation were applied to test outcomes over a wide range of parameters. Using shunt response and complication rates from the literature, the average patient receiving a shunt would gain an additional 1.7 QALYs as a result of automatic shunt insertion. Even if 50% of patients receiving a shunt have complications, the shunt response rate would need to be less than 5% for empirical shunt insertion to do more harm than good. Authors of most studies have reported far better statistics.

CONCLUSIONS

In summary, many more patients with suspected NPH should be considered for shunt insertion.

Intracranial pulse pressure amplitude levels determined during preoperative assessment of subjects with possible idiopathic normal pressure hydrocephalus

BACKGROUND

It was previously reported that the intracranial pulse pressure amplitudes were elevated in idiopathic normal pressure hydrocephalus (iNPH) patients responding to shunt surgery. In this study, pulse pressure amplitudes were determined in all patients referred for tentative iNPH, and patients were selected for shunt surgery based on the determination of their threshold levels of intracranial pulse pressure amplitudes.

PATIENTS AND METHODS

All patients referred to our department for tentative iNPH during a 12 months time period were included. Using intracranial pressure (ICP) monitoring the intracranial pulse pressure amplitudes were determined as the mean wave amplitude in consecutive 6-seconds time windows. Intracranial pulse pressure amplitudes were defined as being elevated when the mean wave amplitudes were either >or=4 mmHg in >or=70%, >or=5 mmHg in >or=40% or >or=6 mmHg in >or=10% of the ICP recording time. Shunt treatment was offered to those with elevated mean wave amplitudes. Clinical state was assessed by using a NPH Grading Scale and the Stein-Langfitt scale before ICP monitoring, and then repeated after 12 months.

RESULTS

Among the 40 iNPH patients included during the 12 months period, the mean wave amplitudes were elevated in 24 patients (60%), while not being elevated in 16 (40%). Neither pre-operative clinical state, radiological ventricular size nor co-morbidity differed between patient groups with elevated or non-elevated mean wave amplitudes. In the shunted patients who had pre-operatively elevated mean wave amplitudes, 91% had very significant clinical change after 12 months (median change in NPH score +4). In those with non-elevated amplitudes and no shunt, clinical state was somewhat worse after 12 months (median change in NPH score -1).

CONCLUSIONS

In this one-year material, mean wave amplitudes were elevated in 60% of iNPH patients. In those with elevated mean wave amplitudes who were treated with shunt, 91% had a significant clinical response.

Intracranial pressure parameters in idiopathic normal pressure hydrocephalus patients treated with ventriculo-peritoneal shunts

BACKGROUND

Although the mean intracranial pressure (ICP) is normal in patients with idiopathic normal pressure hydrocephalus (iNPH), there could possibly be alterations in their single ICP waves.

METHOD

Thirty-nine consecutive patients treated for iNPH with ventriculo-peritoneal shunts were followed prospectively with regard to clinical and radiological findings. Changes in clinical state 12 months after shunt surgery were assessed as change on a 15-3 score NPH Grading Scale, while the changes in ventricular size were assessed by linear measures. The ICP recordings were performed as part of routine pre-operative assessment, stored as raw data files, and analyzed retrospectively. The mean ICP as well as single ICP wave amplitudes were computed and analysed in consecutive 6 second time windows.

FINDINGS

Twelve months after shunt surgery, changes in NPH score of 5 or more (very significant improvement) were observed in 12 patients (31%), of 3 to 4 (significant improvement) in 6 patients (15%), of 1 to 2 (slight improvement) in 9 patients (23%) and of -4 to 0 (non-responders) in 12 patients (31%). The ventricular size did not change in any of the outcome categories. While the pre-operative mean ICP was similar between outcome groups, the mean ICP wave amplitude was significantly higher in patients improving clinically as compared to the non-responders.

CONCLUSIONS

While pre-operative mean ICP was similar, the mean ICP wave amplitudes were significantly higher in iNPH patients improving clinically after shunt treatment as compared to the non-responders.

The role of altered impedance in the pathophysiology of normal pressure hydrocephalus, Alzheimer's disease and syringomyelia

Normal pressure hydrocephalus, Alzheimer's disease and syringomyelia appear to be completely unrelated diseases, however, they share a reduction in subarachnoid space compliance as part of their pathophysiology. This paper discusses the physiology of pulsatile fluid flow and its relationship to compliance/impedance. Unlike continuous or non-pulsatile flow where the vessel resistance and pressure gradient are the major determinants of the volume of fluid flowing, when the fluid flow in a vessel pulsates then the vessel compliance/impedance becomes important. A reduction in compliance in the craniospinal cavity in each of the three diseases discussed, leads to a limitation of the outflow vessel compliance. Therefore, there is an increase in outflow vessel impedance. The venous blood, CSF and interstitial brain/spinal cord fluid all have significantly pulsatile flow and an increase in the impedance of the fluid outflow in each disease would limit the volume of these fluids as they attempt to cross the subarachnoid space. It is hypothesised that a reduction in the efficiency of the outflow of venous blood, CSF and interstitial brain/spinal cord fluid would lead to the accumulation of CSF in NPH, cord fluid in syringomyelia and delay the excretion of beta amyloid via the interstitial drainage pathways in AD.