Cerebral blood flow in normal pressure hydrocephalus

Brain blood flow pulse analysis may help to recognize individuals who suffer from hydrocephalus

BACKGROUND

Normal pressure hydrocephalus (NPH) is often associated with altered cerebral blood flow. Recent research with the use of the ultrasonic method suggests specific changes in the shape of cardiac-related cerebral arterial blood volume (CaBV) pulses in NPH patients. Our study aims to provide a quantitative analysis of the shape of CaBV pulses, estimated based on transcranial Doppler ultrasonography (TCD) in NPH patients and healthy individuals.

METHODS

The CaBV pulses were estimated using TCD cerebral blood flow velocity signals recorded from probable NPH adults and age-matched healthy individuals at rest. The shape of the CaBV pulses was compared to a triangular shape with 27 similarity parameters calculated for every reliable CaBV pulse and compared between patients and volunteers. The diagnostic accuracy of the most prominent parameter for NPH classification was evaluated using the area under the receiver operating characteristic curve (AUC).

RESULTS

The similarity parameters were calculated for 31 probable NPH patients (age: 59 years (IQR: 47, 67 years), 14 females) and 23 healthy volunteers (age: 54 years (IQR: 43, 61 years), 18 females). Eighteen of 27 parameters were different between healthy individuals and NPH patients (p < 0.05). The most prominent differences were found for the ascending slope of the CaBV pulse with the AUC equal to 0.87 (95% confidence interval: 0.77, 0.97, p < 0.001).

CONCLUSIONS

The findings suggest that in NPH, the ascending slope of the CaBV pulse had a slower rise, was more like a straight line, and generally was less convex than in volunteers. Prospective research is required to verify the clinical utility of these findings.

Invention of a non-invasive intracranial pressure (ICP) monitoring system - an enlightenment from a hydrocephalus study

BACKGROUND

Mechanical obstruction is the most common cause of shunt failure for hydrocephalic patients. However, the diagnosis is extremely challenging and often requires invasive testing methods. Thus, a simple and non-invasive technique is in urgent need to predict the intracranial pressure (ICP) of hydrocephalic patients during their post-surgical follow-up, which could help neurosurgeons to determine the conditions of the shunt system.

MATERIALS AND METHODS

Two groups of patients were enrolled in the current study. In group I, patients were enrolled as they were diagnosed with high ICP hydrocephalus and received shunt surgery. The shunt valve pressures were taken for their post-surgical ICP. Meanwhile, the participants of group II exhibited abnormally increased lumbar puncture opening pressure (LPOP; from 180 to 400 mmH₂O). Both the ICP and LPOP were used to match with their corresponding tympanic membrane temperature (TMT).

RESULTS

When patients' ICP were in the normal range (group I, from 50 to 180 mmH₂O), the TMT correlated with ICP in a linear regression model (R² = 0.59, p < 0.001). Interestingly, when patients exhibited above-normal ICP (LPOP was from 180 to 400 mmH₂O), their TMT fit well with the ICP in a third-order polynomial regression (R² = 0.88). When the ICP was 287.98 mmH₂O, the TMT approached the vertex, which was 38.54 °C. Based on this TMT-ICP algorithm, we invented a non-invasive ICP monitor system. Interestingly, a tight linear correlation was detected between the ICP data drawn from the non-invasive device and Codman ICP monitoring system (R² = 0.93, p < 0.01).

CONCLUSIONS

We believe the TMT-ICP algorithm (the Y-Jiang model) could be used for preliminary prediction of shunt malfunction as well as monitoring ICP changes.

Cerebral autoregulation, cerebrospinal fluid outflow resistance, and outcome following cerebrospinal fluid diversion in normal pressure hydrocephalus

OBJECTIVE

Normal pressure hydrocephalus is not simply the result of a disturbance in CSF circulation, but often includes cardiovascular comorbidity and abnormalities within the cerebral mantle. In this study, the authors have examined the relationship between the global autoregulation pressure reactivity index (PRx), the profile of disturbed CSF circulation and pressure-volume compensation, and their possible effects on outcome after surgery.

METHODS

The authors studied a cohort of 131 patients in whom a clinical suspicion of normal pressure hydrocephalus was investigated. Parameters describing CSF compensation and circulation were calculated during the CSF infusion test, and PRx was calculated from CSF pressure and mean arterial blood pressure (MAP) recordings. A simple scale was used to mark the patients’ outcome 6 months after surgery (improvement, temporary improvement, and no improvement).

RESULTS

The PRx was negatively correlated with resistance to CSF outflow (R = -0.18; p = 0.044); patients with normal CSF circulation tended to have worse autoregulation. The correlation for patients who were surgically treated (n = 83) was R = -0.28; p = 0.01, and it was stronger in patients who experienced sustained improvement after surgery (n = 48, R = -0.43; p = 0.002). In patients who did not improve, the correlation was not significantly different from zero (n = 19, R = -0.07; p = 0.97). There was a trend toward higher values for PRx in nonresponders than in responders (0.16 ± 0.04 vs 0.09 ± 0.02, respectively; p = 0.061), associated with higher MAP values (107.2 ± 8.2 in nonresponders vs 89.5 ± 3.5 in responders; p = 0.195). The product of MAP × (1 + PRx), which was proposed as a measure of combined arterial hypertension and deranged autoregulation, showed a significant association with outcome (greater value in nonresponders; p = 0.013).

CONCLUSION

Autoregulation proves to associate with CSF circulation and appears strongest in shunt responders. Outcome following CSF diversion is possibly most favorable when CSF outflow resistance is increased and global cerebral autoregulation is intact, in combination with arterial normotension.

Revisiting secondary normal pressure hydrocephalus: does it exist? A review

OBJECTIVE There are several etiologies that can lead to the development of secondary normal pressure hydrocephalus (sNPH). The aim of this study was to evaluate the etiology, diagnosis, treatment, and outcome in patients with sNPH and to highlight important differences between the separate etiologies. METHODS A comprehensive review of the literature was performed to identify studies conducted between 1965 and 2015 that included data regarding the etiology, treatment, diagnosis, and outcome in patients with sNPH. Sixty-four studies with a total of 1309 patients were included. The inclusion criteria of this study were articles that were written in English, included more than 2 patients with the diagnosis of sNPH, and contained data regarding the etiology, diagnosis, treatment, or outcome of NPH. The most common assessment of clinical improvement was based on the Stein and Langfitt grading scale or equivalent improvement on other alternative ordinal grading scales. RESULTS The main etiologies of sNPH were subarachnoid hemorrhage (SAH) in 46.5%, head trauma in 29%, intracranial malignancies in 6.2%, meningoencephalitis in 5%, and cerebrovascular disease in 4.5% of patients. In 71.9% of patients the sNPH was treated with ventriculoperitoneal shunt placement, and 24.4% had placement of a ventriculoatrial shunt. Clinical improvement after shunt placement was reported in 74.4% and excellent clinical improvement in 58% of patients with sNPH. The mean follow-up period after shunt placement was 13 months. Improvement was seen in 84.2% of patients with SAH, 83% of patients with head trauma, 86.4% of patients with brain tumors, 75% of patients with meningoencephalitis, and 64.7% of patients with NPH secondary to stroke. CONCLUSIONS Secondary NPH encompasses a diverse group of clinical manifestations associated with a subset of patients with acquired hydrocephalus. The most common etiologies of sNPH include SAH and traumatic brain injury. Secondary NPH does indeed exist, and should be differentiated from idiopathic NPH based on outcome and on clinical, pathophysiological, and epidemiological characteristics, but should not be considered as a separate entity.

Current concepts on the pathophysiology of idiopathic chronic adult hydrocephalus: Are we facing another neurodegenerative disease?

INTRODUCTION

Since its description five decades ago, the pathophysiology of idiopathic chronic adult hydrocephalus (iCAH) has been traditionally related to the effect that ventricular dilatation exerts on the structures surrounding the ventricular system. However, altered cerebral blood flow, especially a reduction in the CSF turnover rate, are starting to be considered the main pathophysiological elements of this disease.

DEVELOPMENT

Compression of the pyramidal tract, the frontostriatal and frontoreticular circuits, and the paraventricular fibres of the superior longitudinal fasciculus have all been reported in iCAH. At the level of the corpus callosum, gliosis replaces a number of commissural tracts. Cerebral blood flow is also altered, showing a periventricular watershed region limited by the subependymal arteries and the perforating branches of the major arteries of the anterior cerebral circulation. The CSF turnover rate is decreased by 75%, leading to the reduced clearance of neurotoxins and the interruption of neuroendocrine and paracrine signalling in the CSF.

CONCLUSIONS

iCAH presents as a complex nosological entity, in which the effects of subcortical microangiopathy and reduced CSF turnover play a key role. According to its pathophysiology, it is simpler to think of iCAH more as a neurodegenerative disease, such as Alzheimer disease or Binswanger disease than as the classical concept of hydrocephalus.

In Patients With Idiopathic Normal Pressure Hydrocephalus Postoperative Cerebral Perfusion Changes Measured by Dynamic Susceptibility Contrast Magnetic Resonance Imaging Correlate With Clinical Improvement

OBJECTIVE

To explore relationships between clinical improvement and relative cerebral blood flow (rCBF) changes after shunt-insertion in idiopathic normal pressure hydrocephalus (iNPH) as measured by dynamic susceptibility contrast magnetic resonance imaging.

METHODS

In 20 idiopathic normal pressure hydrocephalus patients rCBF was measured preoperatively and 3 months postoperatively. Because of shunt-induced right-sided artefacts, evaluation was restricted to 12 left-sided cortical, subcortical, and periventricular regions of interest. Correlations between rCBF and clinical symptoms were analyzed in shunt responders.

RESULTS

In responders, the postoperative regions of interest-based rCBF increase of 2% to 9% was significant in the parenchyma, the hippocampus, and the anterior periventricular white matter. Perfusion improvement in the cingulus, caudate head, and thalamus correlated with decreased disturbance in one or more of the domains neuropsychology, gait, balance, and total performance.

CONCLUSIONS

Apparently, dynamic susceptibility contrast magnetic resonance imaging can measure postoperative perfusion changes in responders. Postoperatively, perfusion increase in some grey matter structures seems to determine the degree of clinical improvement.

Endoscopic third ventriculostomy (ETV) for idiopathic normal pressure hydrocephalus (iNPH)

BACKGROUND

Idiopathic normal pressure hydrocephalus (iNPH) is a type of communicating hydrocephalus also known as non-obstructive hydrocephalus. This type of hydrocephalus is caused by impaired cerebrospinal fluid reabsorption without any obstruction in the ventricular system and is associated with normal cerebrospinal fluid pressure. It is characterised clinically by gait disturbance, cognitive dysfunction, and urinary incontinence (known as the Hakim-Adams triad). The exact cause of iNPH is unknown. It may be managed conservatively or treated surgically by inserting a ventriculoperitoneal (VP) or ventriculoatrial (VA) shunt. However, a substantial number of patients do not respond well to surgical treatment, complication rates are high and there is often a need for further surgery. Endoscopic third ventriculostomy (ETV) is an alternative surgical intervention. It has been suggested that ETV may lead to better outcomes, including fewer complications.

OBJECTIVES

To determine the effectiveness of ETV for treatment of patients with iNPH compared to conservative therapy, or shunting of CSF using VP or VA shunts.To assess the perioperative and postoperative complication rates in patients with iNPH after ETV compared to conservative therapy, VP or VA shunting.

SEARCH METHODS

We searched for eligible studies using ALOIS: a comprehensive register of dementia studies, The Cochrane Central Register of Controlled Trials (CENTRAL) and several bibliographic databases such as MEDLINE (Ovid SP), EMBASE (Ovid SP), PsycINFO (Ovid SP), CINAHL (EBSCOhost) and LILACS (BIREME).We also searched the Database of Abstracts of Reviews of Effects (DARE) to identify potentially relevant reviews. The search strategy was adapted for other databases, using the most appropriate controlled vocabulary for each. We did not apply any language or time restrictions. The searches were performed in August 2014.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) of ETV treatment of iNPH. Patients had to have at least two symptoms of the Hakim-Adams triad. Exclusion criteria were obstructive causes of hydrocephalus, other significant intracranial pathology and other confirmed causes of dementia. The eligible comparators were conservative treatment or shunting using VP and VA shunts.

DATA COLLECTION AND ANALYSIS

Two review authors independently screened search results, selected eligible studies, assessed risk of bias and extracted data. We contacted trial authors for additional data.

MAIN RESULTS

Only one study met the inclusion criteria: an RCT comparing effectiveness of ETV and non-programmable VP shunts in 42 patients with iNPH. The study was conducted in Brazil between 2009 and 2012. The overall study risk of bias was high. The primary outcome in the study was the proportion of patients with improved symptoms one year after surgery, determined as a change of at least two points on the Japanese NPH scale. Due to imprecision in the results, it was not possible to determine whether there was any difference between groups in the proportion of patients who improved 3 or 12 months after surgery (3 months: odds ration (OR) 1.12, 95% confidence interval (CI) 0.26 to 4.76, n = 42; 12 months: OR 2.5, 95% CI 0.62 to 10.11, n = 38). We were unable to estimate the effect of treatment on other efficacy outcomes (cognition, balance, function, gait and mobility) because they were inadequately reported. Of the 26 patients in the VP shunting group, 5 developed subdural hematoma postoperatively, while there were no complications among the 16 patients in the ETV group (OR 0.12, 95% CI 0.01 to 2.3, n = 42), but the estimate was too imprecise to determine whether this was likely to reflect a true difference in complication rates. This was also the case for rates of further surgical intervention (OR 1.4, 95% CI 0.31 to 6.24, n = 42). There were no deaths during the trial. We judged the quality of evidence for all outcomes to be very low because of a high risk of selection, attrition and reporting bias and serious imprecision in the results.

AUTHORS' CONCLUSIONS

The only randomised trial of ETV for iNPH compares it to an intervention which is not a standard practice (VP shunting using a non-programmable valve). The evidence from this study is inconclusive and of very low quality. Clinicians should be aware of the limitations of the evidence. There is a need for more robust research on this topic to be able to determine the effectiveness of ETV in patients with iNPH.

Idiopathic normal pressure hydrocephalus: cerebral perfusion measured with pCASL before and repeatedly after CSF removal

Pseudo-continuous arterial spin labeling (pCASL) measurements were performed in 20 patients with idiopathic normal pressure hydrocephalus (iNPH) to investigate whether cerebral blood flow (CBF) increases during the first 24 hours after a cerebrospinal fluid tap test (CSF TT). Five pCASL magnetic resonance imaging (MRI) scans were performed. Two scans were performed before removal of 40 mL CSF, and the other three at 30 minutes, 4 hours, and 24 hours, respectively after the CSF TT. Thirteen different regions of interest (ROIs) were manually drawn on coregistered MR images. In patients with increased CBF in lateral and frontal white matter after the CSF TT, gait function improved more than it did in patients with decreased CBF in these regions. However, in the whole sample, there was no significant increase in CBF after CSF removal compared with baseline investigations. The repeatability of CBF measurements at baseline was high, with intraclass correlation coefficients of 0.60 to 0.90 for different ROIs, but the median regional variability was in the range of 5% to 17%. Our results indicate that CBF in white matter close to the lateral ventricles plays a role in the reversibility of symptoms after CSF removal in patients with iNPH.

Preoperative acetazolamide SPECT is useful for predicting outcome of shunt operation in idiopathic normal pressure hydrocephalus patients

PURPOSE OF THE REPORT

Good outcome of shunt surgery for idiopathic normal pressure hydrocephalus (iNPH) patients are highly dependent on accurate preoperative assessments. Acetazolamide ethylcysteinate-dimer-single photon emission computer tomography (SPECT) was applied to iNPH patients for more exact preoperative evaluation.

PATIENTS AND METHODS

Sixty-five patients were categorized into 3 groups: group I (normals, n = 30), group II (with ventriculomegaly due to age-relating changes, n = 10), and group III (who underwent shunt surgery based on the diagnosis of iNPH, n = 25). Acetazolamide SPECT was performed in all patients, and mini-mental state examination (MMSE) was performed before and 1 month after the surgery in group III.

RESULTS

Acetazolamide SPECT study demonstrated normal increase of cerebral blood flow (CBF, more than 40%) in groups I and II. Group III was classified into 2 subgroups on the examination; a mean increasing percentage (%increase) of CBF was less than 20% in group IIIa and more than 40% in group IIIb. One month after the surgery, acetazolamide SPECT showed normal %increase of CBF in IIIa, and the increase in postoperative MMSE score was significantly greater in group IIIa than IIIb (P < 0.05). In iNPH patients, less than 20% increase in preoperative acetazolamide SPECT predicted improvement of MMSE score with 100% sensitivity and 60% specificity.

CONCLUSIONS

Poor %increase of CBF by acetazolamide implies a low capacity for vasodilation in the brain due to compression and stretching by ventriculomegaly. Acetazolamide SPECT study is not an absolute examination but one of the valuable supplementary objective examinations to determine the surgical indication in iNPH-suspected patients.

Cerebral oxygen metabolism in idiopathic-normal pressure hydrocephalus

OBJECTIVE

To distinguish idiopathic-normal pressure hydrocephalus (i-NPH) from the elder with brain atrophy is difficult. This investigation was undertaken to determine the cerebral oxygen metabolism and the cerebral blood flow using positron emission tomography (PET) in patients with i-NPH. Comparison of the variables between i-NPH patients and the age-comparable control with asymptomatic ventricular dilatation were performed.

METHODS

Nineteen patients were studied. Nine i-NPH patients with a mean age of 74.8 +/- 1.8 years (mean +/- SD) were examined using PET. The subjects who underwent a ventriculoperitoneal shunt (VPS) had the triad of NPH and ventricular dilatation on computed tomography (CT) and/or magnetic resonance imaging (MRI). The results of the PET study were compared with those for ten age-comparable controls (74.8 +/- 5.5 years) with asymptomatic ventricular dilatation and no severe cerebrovascular disease on MRI and magnetic resonance angiography (MRA). The PET study included analyses of regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), regional oxygen extraction fraction (rOEF) and regional cerebral metabolic rate of oxygen (rCMRO(2)).

RESULTS

In i-NPH, rCBF tended to decrease in the frontal lobe and the basal ganglia. rCMRO(2) in the frontal lobe of i-NPH was significantly higher than that in the controls (p<0.05 by Student's t-test), although rCMRO(2) in the basal ganglia of i-NPH was reduced. rCBV and rOEF showed no significant differences.

CONCLUSION

Reduction of oxygen metabolism in the basal ganglia might be one of the factors causing symptoms in i-NPH. Particular pattern of cerebral oxygen metabolism in i-NPH was not obvious in the present study.

A multicenter brain perfusion SPECT study evaluating idiopathic normal-pressure hydrocephalus on neurological improvement

PURPOSE

This study was designed to investigate the specific cerebral blood flow (CBF) pattern in patients with idiopathic normal-pressure hydrocephalus (iNPH) and a predictive value for shunt responsiveness in a multicenter study (Study of Idiopathic Normal-Pressure Hydrocephalus on Neurological Improvement: SINPHONI).

METHODS

Eighty-four iNPH patients underwent shunt operations using MRI selection criteria from the SINPHONI and were subjected to CBF single photon emission computed tomography (SPECT). The perfusion patterns on SPECT were classified: anterior-dominant CBF reduction type (A type), posterior-dominant CBF reduction type (P type), and mixed or diffuse CBF reduction type (M type). The predictive value of the CBF pattern for favorable shunt outcome was evaluated.

RESULTS

Favorable outcomes were obtained in 76% (64/84) of patients, and shunt responsiveness was achieved in 85% (71/84) of patients. Areas of severely reduced relative CBF were demonstrated around the corpus callosum and in the sylvian fissure area, which included the effects of dilatations of the ventricles and sylvian fissures and relatively increased perfusion in the medial and lateral frontal, parietal, and occipital areas at high convexity. Forty-nine (58%) cases were A type, 25 (30%) cases were M type, and 10 (12%) cases were P type. A, M, and P type cases exhibited 83, 84, and 90% positive predictive values for shunt responsiveness, respectively. Mean modified Rankin scale and Mini-Mental State Examination scores of the A type group were significantly better than those of other groups.

CONCLUSION

The iNPH patients showed various patterns of CBF reduction, but there was no significant difference in the predictive value among the three patterns, though CBF reduction patterns may suggest a severe condition of iNPH.

Global cerebral hypoperfusion in preclinical stage of idiopathic normal pressure hydrocephalus

In patients with idiopathic normal pressure hydrocephalus (iNPH), ventriculomegaly and narrowed subarachnoid spaces at the high convexity appear in magnetic resonance (MR) images before the occurrence of objective symptoms. In addition, quantitative regional cerebral blood flow (rCBF) has been reported to be reduced in iNPH patients with objective symptoms. To determine whether reduced rCBF is responsible for the appearance of symptoms, we compared rCBF in patients with suspected iNPH with no objective triad symptoms (NOS), iNPH patients with apparent objective triad symptoms (AOS) and normal control subjects (NC). Regional CBF was quantified in 35 Regions-of-interest (ROIs) by 123I-IMP single photon emission computed tomography (SPECT) using the autoradiography (ARG) method. Multiple comparisons showed that, in all brain regions examined except for in the frontal white matter, rCBF in the NOS group was significantly lower than that in the NC group, but in all brain regions, not significantly different from that of the AOS group. These results suggest that factors other than rCBF in the resting state are responsible for the occurrence of objective symptoms of iNPH.

Cerebrovascular physiology in perinates with congenital hydrocephalus

PURPOSE

This study investigated changes in regional cerebral blood flow (rCBF), autoregulation (AR), and mean CO(2) reactivity (CO(2)r) in nine neonates, who underwent cerebrospinal fluid (CSF) diversion for congenital hydrocephalus.

METHODS

During shunt insertion, a thermal diffusion probe inserted adjacent to the ventricular catheter in the right parietal region recorded rCBF. Changes in rCBF, mean arterial pressure, intracranial pressure (ICP), and expired CO(2) tension were recorded before and after removing CSF.

RESULTS

Mean baseline rCBF for the entire group was 19.5 mL/100 g/min (range 8.4-44.8), with a mean ICP of 9.9 mmHg (range 4-20). Following CSF removal, the rCBF increased significantly in two patients. Three patients demonstrated AR throughout their studies; one infant showed AR after CSF removal. One infant without AR during shunt insertion showed an increase in rCBF and AR during a revision 5 months later. Baseline CO(2)r varied considerably but was greater than two in two patients and increased in three other children after CSF removal. Mean follow-up was 23.6 months. One child, with severe developmental delay, died. Death or severe delay was associated with the absence of AR and a negative CO(2)r in three children. Normal or mild developmental delay was associated with AR and a neutral or positive CO(2)r in five patients.

CONCLUSIONS

Baseline levels of rCBF were not associated with developmental prognosis. AR and a positive CO(2)r were necessary but insufficient factors for normal development. The absence of AR and a negative CO(2)r were associated with poor prognosis.

Ongoing search for diagnostic biomarkers in idiopathic normal pressure hydrocephalus

Idiopathic normal pressure hydrocephalus is a syndrome, which typically has a clinical presentation of gait/balance disturbance, often accompanied by cognitive decline and/or urinary incontinence. Its diagnosis is based on relevant history and clinical examination, appropriate imaging findings and physiological testing. The clinical picture of idiopathic normal pressure hydrocephalus may occasionally be difficult to distinguish from that of Alzheimer’s dementia, subcortical ischemic vascular dementia and Parkinson’s disease. The aim of this article is to systematically review the literature from the last 29 years in order to identify cerebrospinal fluid (CSF) or imaging biomarkers that may aid in the diagnosis of the syndrome. The authors concluded that no CSF or imaging biomarker is currently fulfilling the criteria required to aid in the diagnosis of the condition. However, a few studies have revealed promising CSF and imaging markers that need to be verified by independent groups. The reasons that the progress in this field has been slow so far is also commented on, as well as steps required to apply the current evidence in the design of future studies within the field.

A prospective study of cerebral blood flow and cerebrovascular reactivity to acetazolamide in 162 patients with idiopathic normal-pressure hydrocephalus

OBJECT

Cerebral blood flow (CBF) and cerebrovascular reactivity (CVR) to acetazolamide were investigated prospectively in 162 patients with a proposed diagnosis of idiopathic normal-pressure hydrocephalus (NPH). The aim of this study was to assess the usefulness of the measurement of CBF and CVR in determining which patients would be likely to benefit from shunt placement.

METHODS

The mean CBF of the whole brain was measured according to the Patlak plot method by using technetium-99m hexamethylpropyleneamine oxime. The CVR value was obtained from the response to administration of 500 mg acetazolamide and calculated as the percentage change from the baseline mean CBF value.

RESULTS

One hundred forty-six patients (90.1%) responded to shunt placement ("responders"), but 16 patients (9.9%) did not ("nonresponders"). No significant difference in preoperative CBF was observed between responders and nonresponders. Preoperative CVR was significantly impaired (p<0.0025) in responders compared with healthy controls, but not in nonresponders. Responders with the incomplete triad had a significant reduction (p<0.001) in preoperative CVR, but not in preoperative CBF, compared with healthy controls. Responders with the complete triad had significantly lower preoperative CBF and CVR than those with the incomplete triad (p<0.01 and p<0.05, respectively). Postoperative CBF and CVR increased significantly (p<0.025 and p<0.001, respectively) in responders.

CONCLUSIONS

Both CBF and CVR decrease with the development of NPH, suggesting that hemodynamic ischemia may be responsible for manifestation of the symptoms. Impaired CVR and reduced CBF with the development of symptoms can be proposed as diagnostic criteria for idiopathic NPH.

Longitudinal diffusion-weighted imaging in infants with hydrocephalus: decrease in tissue water diffusion after cerebrospinal fluid diversion

OBJECT

Progressive hydrocephalus may lead to edema of the periventricular white matter and to damage of the brain parenchyma because of compression, stretching, and ischemia. The aim of the present study was to investigate whether cerebral edema can be quantified using diffusion-weighted imaging in infants with hydrocephalus and whether CSF diversion could decrease cerebral edema.

METHODS

Diffusion-weighted MR imaging was performed in 24 infants with progressive hydrocephalus before and after CSF diversion. Parametric images of the trace apparent diffusion coefficients (ADCs) were obtained. The ADCs of 5 different cortical and subcortical regions of interest were calculated pre- and postoperatively in each patient. The ADC values were compared with age-related normal values. Mean arterial blood pressure and anterior fontanel pressure were measured immediately after each MR imaging study.

RESULTS

After CSF diversion, the mean ADC decreased from a preoperative value of 1209 +/- 116 x 10(-6) mm(2)/second to a postoperative value of 928 +/- 64 x 10(-6) mm(2)/second (p < 0.005). Differences between pre- and postoperative ADC values were most prominent in the periventricular white matter, supporting the existence of preoperative periventricular edema. Compared with age-related normal values, the preoperative ADC values were higher and the postoperative ADC values were lower, although within normal range. The decrease in ADC after CSF drainage was more rapid than the more gradual physiological decrease that is related to age. The preoperative ICP was elevated in all patients. After CSF diversion the ICP decreased significantly to within the normal range. A linear correlation between ADC values and ICP was found (correlation coefficient 0.496, p < 0.001). In all patients the mean arterial blood pressure was within physiological limits both pre- and postoperatively.

CONCLUSIONS

This study shows a rapid and more extensive decrease in ADC values after CSF diversion than is to be expected from physiological ADC decrease solely due to increasing patient age. The preoperative ADC increase can be explained by interstitial edema caused by transependymal CSF leakage or by vasogenic edema caused by capillary compression and stretching of the brain parenchyma. This study population of infants with (early recognized) hydrocephalus did not suffer from cytotoxic edema. These findings may help to detect patients at risk for cerebral damage by differentiating between progressive and compensated hydrocephalus.

Noninvasive biomarkers in normal pressure hydrocephalus: evidence for the role of neuroimaging

Object

Normal pressure hydrocephalus (NPH) represents a treatable form of dementia. Recent estimates of the incidence of this condition are in the region of 5% of patients with dementia. The symptoms of NPH can vary among individuals and may be confused with those of patients with multi-infarct dementia, dementia of the Alzheimer type, or even Parkinson disease. Traditionally the diagnosis of NPH could only be confirmed postoperatively by a favorable outcome to surgical diversion of CSF. The object of this literature review was to examine the role of structural and functional imaging in providing biomarkers of favorable surgical outcome.

Methods

A Medline search was undertaken for the years 1980–2006, using the following terms: normal pressure hydrocephalus, adult hydrocephalus, chronic hydrocephalus, imaging, neuroimaging, imaging studies, outcomes, surgical outcomes, prognosis, prognostic value, sensitivity, specificity, positive predictive value, negative predictive value, and accuracy.

Results

The query revealed 16 studies that correlated imaging with surgical outcomes offering accuracy results. Three studies fulfilled the statistical criteria of a biomarker. A dementia Alzheimer-type pattern on SPECT in patients with idiopathic NPH, the presence of CSF flow void on MR imaging, and the N-acetylaspartate/choline ratio in patients with the secondary form are able to predict surgical outcomes with high accuracy.

Conclusions

There is at present Level A evidence for using MR spectroscopy in patients with secondary NPH, and Level B evidence for using SPECT and phase-contrast MR imaging to select patients with idiopathic NPH for shunt placement. The studies, however, need to be repeated by other groups. The current work should act as a platform to design further studies with larger sample sizes.

Cervical spine disease may result in a negative lumbar spinal drainage trial in normal pressure hydrocephalus: case report

OBJECTIVE

In this case report, we present a patient with normal pressure hydrocephalus in whom a lumbar drainage trial yielded a false-negative result secondary to cervical spondylosis.

CLINICAL PRESENTATION

An 80-year-old woman presented with classic symptoms of normal pressure hydrocephalus as well as evidence of cervical myelopathy. Magnetic resonance imaging of the brain and spine showed enlarged ventricles and single-level cervical canal narrowing.

INTERVENTION

An initial lumbar drainage trial was performed, which revealed negative results. The patient then underwent cervical decompression and fusion. Despite this procedure, the patient's symptoms continued to worsen. A repeat lumbar drainage trial was performed with positive results. Subsequently, a ventriculoperitoneal shunt was placed, resulting in significant improvement of her symptoms.

CONCLUSION

This case report illustrates how altered cerebrospinal fluid flow dynamics may impact the accuracy of the lumbar spinal drainage trial in patients with normal pressure hydrocephalus.

Magnetic resonance imaging for quantitative flow measurement in infants with hydrocephalus: a prospective study

OBJECT

Raised intracranial pressure (ICP) that is associated with hydrocephalus may lead to alterations in cerebral hemodynamics and ischemic changes in the brain. In infants with hydrocephalus, defining the right moment for surgical intervention based on clinical signs alone can sometimes be a difficult task. Clinical signs of raised ICP are known to be unreliable and sometimes even misleading. Furthermore, when sutures are closed, ICP does not always correlate with the size of the ventricles or with the clinical signs or symptoms. In this study the authors investigated whether cerebral blood flow (CBF) can be measured by using quantitative MR angiography in infants with progressive hydrocephalus. In addition, the authors investigated the relationship between CBF and ICP, before and after cerebrospinal fluid (CSF) diversion.

METHODS

Fifteen infants with progressive hydrocephalus (age range 1 day-7 months) were examined. All patients underwent anterior fontanel pressure measurement, MR angiography, and mean arterial blood pressure measurements before and after CSF diversion. Brain volume was measured to compensate for the physiological increase in CBF during brain maturation in infants.

RESULTS

The mean preoperative ICP was 19.1 +/- 8.4 cm H(2)O (+/- standard deviation). The mean postoperative ICP was 6.7 +/- 4.0 cm H(2)O (p < 0.005). The mean preoperative CBF was 25.7 +/- 11.3 ml/100 cm(3) brain/min. After CSF diversion, CBF increased to 50.1 +/- 12.1 ml/100 cm(3) brain/min (p < 0.005). The mean arterial blood pressure did not change after surgical intervention.

CONCLUSIONS

Magnetic resonance imaging can be used to measure CBF in infants with hydrocephalus. Raised ICP was related to a decrease in CBF. After CSF diversion, CBF and ICP improved to values within the normal range.

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.

Brain metabolism in adult chronic hydrocephalus

Normal pressure hydrocephalus (NPH) is the most frequent form of chronic hydrocephalus in adults. NPH remains underdiagnosed although between 5% and 10% of all demented patients may suffer from this disorder. As dementia is an increasing demographic problem, treatable forms such as in NPH have become a central issue in neurology. Despite the traditional perception of hydrocephalus being a disorder of disturbed CSF dynamics, in NPH metabolic impairment seems at least as important. So far, the only valid animal model of NPH is chronic adult kaolin hydrocephalus. In this model, opening of alternative CSF outflow pathways leads to normal or near-normal intracranial pressure and CSF outflow resistance. Yet, various metabolic disturbances cause ongoing ventricular enlargement and characteristic symptoms including cognitive decline and gait ataxia. Delayed hippocampal neuronal death, accumulation of beta-amyloid and disturbed cholinergic neurotransmission may contribute to memory dysfunction. Compromised periventricular blood flow, decreased dopamine levels in the substantia nigra and damaged striatal GABAergic interneurons may reflect basal ganglia symptoms. At least in human hydrocephalus cerebrovascular co-morbidity of the white matter plays an important role as well. It seems that in hydrocephalus from a certain 'point of no return' metabolic impairment becomes decoupled from CSF dynamics and, at least partly, self-sustained. This is probably the reason why despite restored CSF circulation by shunting many patients with chronic hydrocephalus still suffer from severe neurological deficits. The present paper offers a comprehensive review of the experimental and clinical data suggesting metabolic disturbances in chronic hydrocephalus.

Chronic hydrocephalus-induced hypoxia: increased expression of VEGFR-2+ and blood vessel density in hippocampus

Chronic hydrocephalus (CH) is a neurological disease characterized by increased cerebrospinal fluid volume and pressure that is often associated with impaired cognitive function. By and large, CH is a complex and heterogeneous cerebrospinal fluid (CSF) disorder where the exact site of brain insult is uncertain. Several mechanisms including neural compression, fiber stretch, and local or global hypoxia have been implicated in the underlying pathophysiology of CH. Specifically, the hippocampus, which plays a significant role in memory processing and is in direct contact with expanding CSF ventricles, may be involved. Using our model of chronic hydrocephalus, we quantified the density of vascular endothelial growth factor receptor 2 (VEGFR-2(+)) neurons, glial, endothelial cells, and blood vessels in hippocampal regions CA1, CA2-3, dentate gyrus and hilus using immunohistochemical and stereological methods. Density and %VEGFR-2(+) cell populations were estimated for CH animals (2-3 weeks vs. 12-16 weeks) and surgical controls (SC). Overall, we found approximately six- to eightfold increase in the cellular density of VEGFR-2(+) and more than double blood vessel density (BVd) in the hippocampus of CH compared with SC. There were no significant regional differences in VEGFR-2(+) cellular and BVd expression in the CH group. VEGFR-2(+) and BVds were significantly related to changes in CSF volume (P<or=0.05), and not intracranial pressure (ICP). The %VEGFR-2(+) was significantly greater in CH than SC (P<or=0.05), and was significantly correlated with BVd (P<or=0.05). These results showed that CH elicited a profound increase in VEGFR-2(+) in hippocampus that corresponded to increased BVd. It was unclear whether increased VEGFR-2(+) and blood vessel expression was related to focal compression alone or in combination with global ischemia/hypoxia conditions as previously described. These findings suggest that VEGFR-2 may play an adaptive role in angiogenesis after CH-induced hypoxia. Modulation of vascular endothelial growth factor/VEGFR-2(+) may be important in developing treatments for hypoxic conditions including hydrocephalus and other forms of cerebral ischemia.

The pathophysiology of idiopathic normal pressure hydrocephalus: cerebral ischemia or altered venous hemodynamics?

BACKGROUND AND PURPOSE

Many theories of normal pressure hydrocephalus (NPH) stress the importance of ischemia in the deep white matter. Alternate theories stress a reduction in superficial venous compliance and changes in pulse-wave propagation. An overlap in the cerebral blood flow volumes measured between NPH and controls suggests that ischemia may not be a prerequisite for this condition. This study sought to compare blood flow and compliance measures in a cohort of patients with NPH selected for having arterial inflows above the normal range to see if deep brain ischemia or superficial hemodynamic changes contribute to the pathophysiology of NPH.

MATERIALS AND METHODS

Twenty patients with NPH and arterial inflows above the normal range were selected. They underwent MR imaging with flow quantification measuring the total blood inflow, sagittal/straight sinus outflow, aqueduct stroke volume, and arteriovenous delay (AVD). Patients were compared with 12 age-matched controls.

RESULTS

The deep outflow volumes were normal. The superficial venous outflow was reduced as a percentage of the inflow by 9% (P = .04). The sagittal sinus compliance as measured by the AVD was reduced by 50% (P = .0001), and the aqueduct stroke volume was elevated by 192% (P = .02).

CONCLUSION

Ischemia in the deep venous territory is not a prerequisite for NPH. Patients with high-inflow NPH show alterations in superficial venous compliance and a reduction in the blood flow returning via the sagittal sinus. These changes together suggest that an elevation in superficial venous pressure may occur in NPH.

Predictive assessment of shunt effectiveness in patients with idiopathic normal pressure hydrocephalus by determining regional cerebral blood flow on 3D stereotactic surface projections

BACKGROUND

The regional cerebral blood flow (rCBF) and cerebral metabolism in patients with idiopathic normal pressure hydrocephalus (iNPH) remain to be studied in detail.

PURPOSE

Using single-photon emission computed tomography (SPECT), we compared the characteristic rCBF patterns in iNPH patients who did, or did not, respond to shunt operations.

MATERIALS AND METHODS

We studied 24 consecutive iNPH patients: 14 men and 10 women aged 68 to 88 years (mean 77.5 years). Using the Japanese normal pressure hydrocephalus grading scale, they were divided into responders and non-responders to shunt operations. Follow-up ranged from 10 to 36 months (mean 25 months). We obtained baseline single-photon emission computed tomography (SPECT) data on three-dimensional stereotactic surface projections (3D-SSP) before and after shunt operations, and compared rCBF in responders and non-responders.

RESULTS

On statistical maps, responders manifested significantly lower rCBF in the basal frontal lobes and cingulate gyrus (anterior-dominant).

CONCLUSIONS

The preoperative measurement of rCBF by 3D-SSP SPECT may help to identify iNHP patients expected to exhibit a good response to shunt operations.

Oxygen metabolism changes in patients with idiopathic normal pressure hydrocephalus before and after shunting operation

OBJECTIVE

The present study revealed the changes in cerebral oxygen metabolism before and after ventriculo-peritoneal shunt (VPS) using (15)O positron emission tomography ((15)O-PET).

METHODS

Eight patients with idiopathic normal pressure hydrocephalus (i-NPH) underwent VPS. A (15)O-PET study was undertaken before and approximately 3 months after VPS. In five patients, the symptoms improved based on the classification by Krauss et al. [Neurosurgery 1996;39:292] (good responders) after VPS. In three patients, the symptoms improved subjectively following VPS (poor responders). The changes in oxygen metabolism before and after VPS were analyzed.

RESULTS

The postoperative regional cerebral metabolic rate of oxygen (rCMRO(2)) of the good responders increased significantly. The postoperative regional oxygen extraction fraction (rOEF) is reduced in the poor responders.

CONCLUSION

The improvement of rCMRO(2) correlated with the response to VPS. Significant changes in rOEF might predict poor response to VPS.

Cerebral perfusion pattern of idiopathic normal pressure hydrocephalus studied by SPECT and statistical brain mapping

OBJECTIVES

To investigate the specific pattern of cerebral blood flow (CBF) in subjects with idiopathic normal pressure hydrocephalus (iNPH) using voxel-based analysis.

METHODS

N-isopropyl-p-[123I]iodoamphetamine (IMP) single photon emission computed tomography (SPECT) images were performed in 30 iNPH patients, who met probable iNPH criteria, 30 Alzheimer disease (AD) patients and 15 normal control (NC) subjects. Inter-group comparisons between iNPH patients and NC subjects and between AD patients and NC subjects were performed using three-dimensional stereotactic surface projection (3D-SSP) analysis. Individual 3D-SSP images of the iNPH patients were assessed by visual inspection.

RESULTS

On the Z-score maps, areas of relative hypoperfusion were recognized around the corpus callosum in all 30 iNPH patients, as well as in the Sylvian fissure regions in 19 of 30 iNPH patients which included artifacts by dilated ventricles and the Sylvian fissures. Ten frontal dominant, eight parietotemporal dominant, and 12 diffuse hypoperfusion types were demonstrated. Inter-group comparison between iNPH and NC subjects showed relative hypoperfusion in the frontal and parietotemporal areas and severe hypoperfusion around the corpus callosum and Sylvian fissure regions, while parietotemporal and posterior cingulate CBF reduction was demonstrated between the AD and NC groups.

CONCLUSION

Voxel-based analysis showed a characteristic pattern of regional CBF reduction with frontal dominant or diffuse cerebral hypoperfusion accompanying severe hypoperfusion around the corpus callosum and Sylvian fissures with artifacts.

Pathophysiology of Cerebral Circulatory Disorders in Idiopathic Normal Pressure Hydrocephalus

This study was conducted to elucidate the pathologic conditions of cerebral circulatory disorders in idiopathic normal pressure hydrocephalus (iNPH). Among 44 possible iNPH patients, 40 patients underwent shunt surgery based on diagnostic flow charts plotted by the Southern Tohoku method and were evaluated to be shunt-effective at the end of the first post-surgical month. The cerebral blood flow (CBF) was measured by N-isopropyl-((123)I)-P-iodo-amphetamine single photon emission computed tomography (mean, mCBF; cortical region, cCBF; thalamus-basal ganglia region, tbCBF on autoradiography [ARG] method) and the perfusion patterns of the cerebral cortex were measured based on three-dimensional stereotactic surface projection (3D-SSP) Z-score images, before and 1 month after the surgery in all 40 subjects. The mCBF rose significantly from 32.1 +/- 2.74 ml/100 g/min before surgery to 39.8 +/- 3.02 ml/100 g/min after surgery (p < 0.03). Investigation of the change of CBF revealed reductions in the cCBF (3 cases), tbCBF (9 cases), and cCBF + tbCBF (28 cases), with the reduced-cCBF group totaling 31 cases and the reduced-tbCBF group totaling 37 cases. Investigation of cerebral cortex hypoperfusion by 3D-SSP Z-score revealed 31 cases with hypoperfusion (frontal lobe type [19 cases], occipitotemporal lobe type [5 cases], mixed type [7 cases]) and nine cases with cortical normoperfusion (N). The pattern of reduction of the cortical blood flow on ARG method was favorably correlated with the pattern of hypoperfusion of the cerebral cortex on 3D-SSP Z-score images before surgery. A reduction of blood flow was found in the thalamus-basal ganglia region of all N type cases. The blood flow improved in 19 of 31 (61.3%) cases of the reduced-cCBF group and in 32 of 37 (86.5%) cases of the reduced-tbCBF group. All of the cases without detectable improvement exhibited increased blood flow in non-reduction areas. Investigation of the hypoperfusion patterns of the cerebral cortex on 3D-SSP Z-score images, revealed a reduction or disappearance of the hypoperfusion site in 19 of 31 (61.3%) cases, either no-change or a shift of the hypoperfusion site in 12 of 31 (38.7%) cases, and a correlation between the pattern of cortical blood flow reduction on ARG method and the pattern of cerebral cortex hypoperfusion on 3D-SSP Z-score images after surgery. Cerebral circulatory disorders in iNPH manifest as either of two pathophysiological conditions: the "circulatory disorder of the cerebral cortical region" and the "circulatory disorder of the thalamus-basal ganglia region." Various patterns develop according to the disease stage.

Chronic hydrocephalus-induced changes in cerebral blood flow: mediation through cardiac effects

Decreased cerebral blood flow (CBF) in hydrocephalus is believed to be related to increased intracranial pressure (ICP), vascular compression as the result of enlarged ventricles, or impaired metabolic activity. Little attention has been given to the relationship between cardiac function and systemic blood flow in chronic hydrocephalus (CH). Using an experimental model of chronic obstructive hydrocephalus developed in our laboratory, we investigated the relationship between the duration and severity of hydrocephalus and cardiac output (CO), CBF, myocardial tissue perfusion (MTP), and peripheral blood flow (PBF). Blood flow measures were obtained using the microsphere injection method under controlled hemodynamic conditions in experimental CH (n=23) and surgical control (n=8) canines at baseline and at 2, 4, 8, 12, and 16 weeks. Cardiac output measures were made using the Swan-Ganz thermodilution method. Intracranial compliance (ICC) via cerebrospinal fluid (CSF) bolus removal and infusion, and oxygen delivery in CSF and prefrontal cortex (PFC) were also investigated. We observed an initial surgical effect relating to 30% CO reduction and approximately 50% decrease in CBF, MTP, and PBF in both groups 2 weeks postoperatively, which recovered in control animals but continued to decline further in CH animals at 16 weeks. Cerebral blood flow, which was positively correlated with CO (P=0.028), showed no significant relationship with either CSF volume or pressure. Decreased CBF correlated with oxygen deprivation in PFC (P=0.006). Cardiac output was inversely related with ventriculomegaly (P=0.019), but did not correlate with ICP. Decreased CO corresponded to increased ICC, as measured by CSF infusion (P=0.04). Our results suggest that CH may have more of an influence on CO and CBF in the chronic stage than in the early condition, which was dominated by surgical effect. The cause of this late deterioration of cardiac function in hydrocephalus is uncertain, but may reflect cardiac regulation secondary to physiologic response or brain injury. The relationship between cardiac function and CBF should be considered in the pathophysiology and clinical treatment of CH.

Amplitude and phase of cerebrospinal fluid pulsations: experimental studies and review of the literature

OBJECT

A recently developed model of communicating hydrocephalus suggests that ventricular dilation may be related to the redistribution of pulsations in the cranium from the subarachnoid spaces (SASs) into the ventricles. Based on this model, the authors have developed a method for analyzing flow pulsatility in the brain by using the ratio of aqueductal to cervical subarachnoid stroke volume and the phase of cerebrospinal fluid (CSF) flow, which is obtained at multiple locations throughout the cranium, relative to the phase of arterial flow.

METHODS

Flow data were collected in a group of 15 healthy volunteers by using a series of images acquired with cardiac-gated, phase-contrast magnetic resonance imaging. The stroke volume ratio was 5.1 +/- 1.8% (mean +/- standard deviation). The phase lag in the aqueduct was -52.5 +/-16.5 degrees and the phase lag in the prepontine cistern was -22.1 +/- 8.2 degrees. The flow phase at the level of C-2 was -5.1 +/- 10.5 degrees, which was consistent with flow synchronous with the arterial pulse. The subarachnoid phase lag ventral to the pons was shown to decrease progressively to zero at the craniocervical junction. Flow in the posterior cervical SAS preceded the anterior space flow.

CONCLUSIONS

Under normal conditions, pulsatile ventricular CSF flow is a small fraction of the net pulsatile CSF flow in the cranium. A thorough review of the literature supports the view that modified intracranial compliance can lead to redistribution of pulsations and increased intraventricular pulsations. The phase of CSF flow may also reflect the local and global compliance of the brain.

Gravitational shunts in longstanding overt ventriculomegaly in adults

OBJECTIVE

A new entity of chronic hydrocephalus was introduced recently in the international literature: longstanding overt ventriculomegaly in adults. Previous experience with this disorder has demonstrated that shunt therapy for such patients involves a considerable risk of overdrainage. In the present study, we aimed to clarify whether this risk could be avoided by use of gravitational shunts.

METHODS

A total of 26 adults (age range, 17-75 yr) with macrocephaly and progressive hydrocephalus symptoms underwent implantation of either an adjustable Codman Hakim gravity-assisted shunt (Codman Medos, LeLocle, Switzerland) plus an Aesculap-Miethke ShuntAssistant (Miethke KG, Kleinmachnow, Germany) or a nonadjustable gravitational shunt (Aesculap-Miethke gravity-assisted valve). The follow-up period averaged 29 +/- 13 months (range, 6-48 mo).

RESULTS

Significant sustained clinical improvement was achieved in 87% of patients. In more than 90% of patients, Evans index decreased postoperatively by less than 10%. No correlation was documented between the degree of ventricle width reduction and clinical improvement. Only two patients developed subdural hematoma, which was caused by insufficient hydrostatic pressure compensation owing to errors in estimation of intraperitoneal pressure.

CONCLUSION

Unlike conventional differential pressure shunts, gravitational shunts can be used in the treatment of high-risk patients with longstanding overt ventriculomegaly in adults. Significant risk of overdrainage can be avoided. Gravitational shunts offer a viable alternative to endoscopic third ventriculostomy, provided the choice and adjustment of the shunt opening pressure is based on a correct assessment of the hydrostatic pressure to be compensated for.

Voxel-based assessment of spinal tap test-induced regional cerebral blood flow changes in normal pressure hydrocephalus

OBJECTIVE

Normal pressure hydrocephalus (NPH) is a cause of dementia that may be amended by medical intervention. Its diagnosis is therefore of major importance and the establishment of response criteria to cerebrospinal fluid (CSF) shunting is essential. One of these criteria is the clinical response to spinal tap. The accuracy of the spinal tap test could potentially be improved by adding neuroimaging of regional cerebral blood flow (rCBF) changes to the response criteria. Statistical parametric mapping (SPM) is a voxel-based method of image analysis that may be used to statistically assess the significance of rCBF changes. The objective of this study was to evaluate, by SPM, spinal tap test-induced rCBF changes in patients with NPH syndrome.

METHODS

Forty patients with NPH syndrome underwent hexamethylpropylene amine oxime (HMPAO) brain single photon emission computed tomography (SPECT) before and after a spinal tap test (1-day split-dose protocol). The differences in rCBF between these pairs of scans were analysed by SPM in the whole group and between subgroups divided according to gait improvement at the spinal tap test.

RESULTS

In the whole group of patients, there was no statistical difference between pre- and post-spinal tap SPECT images. SPM analysis of patients grouped as a function of their clinical response to the spinal tap test revealed a significant post-spinal tap rCBF increase in the bilateral dorsolateral frontal and left mesiotemporal cortex in clinically responding compared with non-responding patients.

CONCLUSION

According to SPM analysis, gait improvement at the spinal tap test in patients with NPH syndrome is associated with an rCBF increase localized in the bilateral dorsolateral frontal and left mesiotemporal cortex.

Alteration of cerebral perfusion in patients with idiopathic normal pressure hydrocephalus measured by 3D perfusion weighted magnetic resonance imaging

OBJECTIVE

It is controversial whether alteration of cerebral perfusion plays an important role in the pathophysiology of patients with idiopathic normal pressure hydrocephalus (NPH) and can help to predict the outcome after shunt surgery.

MATERIALS AND METHODS

28 patients with suspected NPH were examined clinically (Homburg Hydrocephalus Scale, walking test, incontinence protocol) and by 3D dynamic susceptibility based perfusion weighted magnetic resonance imaging (PWI-MRI) before and after cerebrospinal fluid release (spinal tap test, STT). The perfusion parameters (negative integral (NI), time of arrival (T0), time to peak (TTP), mean transit time, and the difference TTP-T0 were analysed.

RESULTS

Three different groups of patients were identified preoperatively: In group 1 seven patients showed an increase in the cerebral perfusion and a clinical improvement after STT. The second group (9 patients) also revealed an increase of the cerebral perfusion, but no significant alteration of the clinical assessment could be found. In the third group neither the cerebral perfusion nor the clinical assessment changed. 14 of the 16 patients (group 1 and 2) were examined three months after shunt placement. 11 patients showed a good or excellent result, 2 patients revealed a fair assessment, and only 1 patient had transiently improved. No patient was downgraded after shunting. In the patient group 1 and 2 the NI increased significantly (effect size: 34%), whereas in group 3 no significant alteration of NI was observed.

CONCLUSION

PWI-MRI improves the prediction of outcome after shunt placement in patients with NPH and can offer new insights into the pathophysiology.

Impaired wakefulness is associated with reduced anterior cingulate CBF in patients with normal pressure hydrocephalus

OBJECTIVE

To evaluate if impaired wakefulness (IW) in normal pressure hydrocephalus (NPH) is associated with reduced blood flow in regions associated with the brain arousal system.

METHOD

NPH (n = 28) patients were studied before and after surgery. Wakefulness was assessed using a new developed scale. Relative regional cerebral blood flow (rrCBF) was quantified using SPECT and rectangular regions of interest analysis.

RESULTS

Sixteen patients presented with IW at baseline and in 14 of these, IW vanished after surgery. Patients presenting with IW had reduced rrCBF in the anterior cingulate cortex compared with those without. After surgery, rrCBF increased significantly in thalamic, frontal and hippocampal grey matter regions. Increased hippocampal rrCBF correlated with increased basal frontal rrCBF (r = 0.64). In patients where IW vanished after surgery, rrCBF increased in the mesencephalon, hippocampus and the frontal association cortex. The postoperative increase in wakefulness correlated with increased rrCBF in frontal (r = 0.74) and parietal (r = 0.65) association cortex areas.

CONCLUSION

IW in NPH is associated with reduced rrCBF in the anterior cingulate cortex. Improved wakefulness following surgery corresponds to rrCBF increments in the frontal association cortex. This study provides support for a functional coupling between frontal, hippocampal, thalamic and mesencephalic rrCBF in NPH at large.

Cerebral blood oxygenation after cerebrospinal fluid removal in hydrocephalus measured by near infrared spectroscopy

BACKGROUND

The cerebrospinal fluid (CSF) tap test has been used for the diagnosis of chronic hydrocephalus to identify the candidates for surgical CSF shunting. However, a high rate of false negative results limits it utility. The purpose of this study is to investigate whether the concomitant monitoring of cerebral hemodynamics by near infrared spectroscopy (NIRS) can improve the diagnostic accuracy of the tap test.

METHODS

Thirteen patients with dilated ventricular system were candidates for this study. We assessed for the patterns of cerebral blood oxygenation (CBO) change in hydrocephalus to determine whether CBO change after CSF removal is useful for selecting shunt candidates.

RESULTS

Patients who showed clinical improvement following CSF shunting had a characteristic CBO change with increases in the concentration of oxyhemoglobin (Oxy-Hb), and patients without improvement during continuous CSF drainage test showed no increase in Oxy-Hb.

CONCLUSION

The current data suggests that CBF increases after CSF removal in hydrocephalus. Although the patients utilized in the present study had secondary chronic hydrocephalus, we speculate that these data could be applied to patients with idiopathic chronic hydrocephalus. Further investigation would be of benefit.

Cerebrospinal fluid dynamics

Hydrocephalus is far more complicated than a simple disorder of CSF circulation. Historically, it has been diagnosed using clinical and psychomotor assessment plus brain imaging. The role of physiological measurement to aid diagnosis becomes more appreciated in current clinical practice. This has been reflected by recently formulated guidelines for the management of normal pressure hydrocephalus. Clinical measurement in hydrocephalus is mainly related to intracranial pressure (ICP) and cerebral blood flow. This review lists and discusses most common forms of the methods: CSF infusion study, overnight ICP monitoring, assessment of slow ICP waves, testing pressure reactivity, cerebral autoregulation, CO2 reactivity and PET-CBF studies combined with MRI co-registration. The basics of CSF dynamics modelling are presented and the principles of the assessment of functioning of the implanted hydrocephalus shunts are also discussed. The descriptions of multiple forms of measurement along with clinical illustrations are mainly based on in-house experience of a multidisciplinary group of scientists and clinicians from Cambridge, UK.

Pattern of white matter regional cerebral blood flow and autoregulation in normal pressure hydrocephalus

The mean cerebral blood flow (CBF) has generally been demonstrated to be lower in normal pressure hydrocephalus (NPH) than in normal controls. We investigated the distribution of the regional peri- and paraventricular white matter CBF (WM CBF) in NPH at baseline and during a controlled rise in intracranial pressure (ICP). Twelve patients with idiopathic NPH (mean age 69 years) underwent a CSF infusion study. CBF was measured by H2(15)O PET at baseline and then during the steady-state plateau of raised ICP. The PET images were co-registered and resliced to 3D structural T1-weighted MRIs. Ten healthy normal volunteers served as control subjects for baseline CBF determination only. Profiles of the regional distribution of the baseline WM CBF and of the percentage change in WM CBF as a function of distance from the ventricles were plotted. The global mean baseline CBF in patients (28.4 +/- 5.2 ml/100 ml/min) was lower than in the control subjects (33 +/- 5.4 ml/100 ml/min) (P < 0.005). In patients, the profile of the regional WM CBF at baseline showed an increase with distance from the ventricles (P < 0.0001), with a maximal reduction adjacent to the ventricles and progressive normalization with distance, whereas in controls no relationship was apparent (P = 0.0748). In 10 patients, the rise in ICP during the infusion produced a fall in cerebral perfusion pressure (CPP) and a significant decrease of the global mean CBF from 27.6 +/- 3.1 to 24.5 +/- 2.9 ml/100 ml/min (P < 0.0001). The profile of the percentage changes in regional WM CBF in patients showed a U-shaped relationship with distance from the ventricles (P = 0.0007), with a maximal decrease skewed on the side of the lateral ventricles at around a mean distance of 9 mm. The WM CBF is reduced in NPH, with an abnormal gradient from the lateral ventricles towards the subcortical WM. An excessive decrease in CBF is brought about by reductions in CPP and appears to be maximal in the paraventricular watershed region. These results are discussed in the light of previous hypotheses concerning the aetiology of periventricular CBF reduction in NPH.

Intracranial Fluid Dynamics in Normal and Hydrocephalic States

OBJECTIVE

To present a novel magnetic resonance (MR) method of analysis of cerebrospinal fluid (CSF) flow dynamics.

METHODS

Fifty-one subjects were explored with phase-contrast cine MR imaging. There were 36 volunteers, 9 patients with normal pressure hydrocephalus (NPH), and 6 patients with asymptomatic ventricular dilation (VD). The transfer function XFRA/CSF from the arterial pulse waves (APWs) and the CSF pulse waves (CSFPWs) and the transfer function XFRCSF/SS from the CSF pulse waves (CSFPWs) and the sagittal sinus pulse waves (SSPWs) were studied separately.

RESULTS

There was a significant difference in the amplitude spectrum of the XFRA/CSF of patients with VD and volunteers (P < 0.05) and in that of patients with NPH and volunteers (P = 0.005). The amplitude of the fundamental frequency was higher in the NPH group than in the VD group (P = 0.02). In patients with NPH, the amplitude spectrum of XFRCSF/SS showed an attenuation of the pulse wave components that significantly differed from the observed amplification in healthy subjects (P = 0.009) and patients with VD (P = 0.012).

CONCLUSION

This systems analysis method could help to detect increased venous compliance in VD and decreased venous compliance in NPH.

Multi-modal MRI in normal pressure hydrocephalus identifies pre-operative haemodynamic and diffusion coefficient changes in normal appearing white matter correlating with surgical outcome

Magnetic resonance techniques were used to investigate haemodynamic abnormalities and their consequences in normal pressure hydrocephalus (NPH) and to assess changes in these parameters following surgery. Eleven patients with NPH were studied pre- and post-operatively using perfusion and diffusion weighted imaging and compared with ten age-matched controls. Pre-operative periventricular relative cerebral blood volume (rCBV) was reduced in patients (0.76+/-0.11) compared with control (1.16+/-0.16, P<0.01). There was no difference between outcome groups and no change in haemodynamic parameters following surgery. The periventricular apparent diffusion coefficient (ADC) was elevated in the poor outcome group (1.67+/-0.3 x 10(-3) mm(2) s(-1)) compared with both controls (1.04+/-0.4 x 10(-3) mm(2) s(-1), P<0.05) and the good outcome group (0.99+/-0.3 x 10(-3) mm(2) s(-1), P<0.05) despite appearing normal on conventional imaging. In white matter hyperintensities (WMH), rCBV was reduced (0.70+/-0.12 vs. 1.00+/-0.10, P<0.01), and the ADC was increased (1.98+/-0.6 vs. 1.04+/-0.4 x 10(-3) mm(2) s(-1), P<0.05) compared with the same anatomical location in controls. As low rCBV and high ADC is characteristic of chronic infarction, the findings in WMH regions suggest they are irreversibly damaged. Normal appearing periventricular tissue rCBV was reduced, implying that significant haemodynamic consequences contribute to symptoms in NPH. The elevated pre-operative ADC of the same region, was correlated with poor outcome, and may, therefore, be useful in selecting patients for surgery.

Is a combination of Tc-SPECT or perfusion weighted magnetic resonance imaging with spinal tap test helpful in the diagnosis of normal pressure hydrocephalus?

OBJECTIVE

The aim of this study was to evaluate the combination of spinal tap test (STT) with cerebral perfusion measurement assessed either by Tc-bicisate-SPECT (Tc-SPECT) or perfusion weighted MRI (pwMRI), or both, for a better preoperative selection of promising candidates for shunt operations in suspected idiopathic normal pressure hydrocephalus.

METHODS

27 consecutive patients were examined with a standard clinical protocol (assessed by the Homburg Hydrocephalus Scale (HHS)) as well as with 99m Tc-bicisate-SPECT (n=27) or additionally by pwMRI (n=12) before and after STT. The results of these examinations were compared preoperatively for each patient and correlated with postoperative clinical outcome after shunt surgery.

RESULTS

Nine patients showed both, a clinical improvement, and increased cerebral perfusion after STT. They underwent shunt surgery with good to excellent results. In another nine patients increasing cerebral perfusion was detected although they did not show a clear clinical improvement after STT. Six of them also received a shunt operation with good to excellent outcome. Three patients of the last group could have an operation. Nine patients did not show any clinical improvement or any kind of increasing cerebral perfusion after STT. Therefore, they did not undergo surgery. The results of SPECT and pwMRI correlated in 92 % of the patients (11 of 12).

CONCLUSION

It is concluded that a combination of clinical assessment with SPECT or pwMRI is helpful in the preoperative selection of patients for shunting procedures with suspected NPH syndrome. This combination is a minimal invasive and objective test modality that is superior to STT alone. Further studies are necessary for a comparison of the described imaging techniques with different diagnostic tests in this difficult field of cerebral disease.

Cerebral hemodynamics before and after shunting in normal pressure hydrocephalus

OBJECTIVE

To study the relationship between cerebral hemodynamics and clinical performance in normal pressure hydrocephalus (NPH), before and after surgery.

MATERIAL AND METHODS

Ten patients were studied prospectively before and 3 months after shunt surgery by means of transcranial Doppler (TCD). Clinical performance was scored by means of an NPH scale and the modified Rankin scale.

RESULTS

Peak systolic and mean cerebral blood flow velocity (MCV) were lower and cerebrovascular CO2 reactivity was higher after shunt surgery. The three patients with clinical improvement had higher preoperative end diastolic cerebral blood flow velocity and MCV. All postoperative cerebral blood flow velocities were higher in patients with clinical improvement.

CONCLUSION

Our data suggest that higher cerebral blood flow velocity before surgery in patients with NPH is related to clinical improvement after shunt surgery. Cerebral hemodynamic parameters may develop into predictors of successful shunt surgery in patients with normal pressure hydrocephalus.

Cerebral autoregulation among patients with symptoms of hydrocephalus

OBJECTIVE

To study the relationship between the resistance to cerebrospinal fluid (CSF) outflow and cerebral autoregulation.

METHODS

We examined 35 patients who presented with ventricular dilation and clinical symptoms of communicating hydrocephalus. For all of these patients, CSF compensatory reserve was investigated by using a computerized infusion test, with simultaneous recording of blood flow velocity wave forms (by using transcranial Doppler ultrasonography) and arterial blood pressure (with a Finapress finger cuff). The resistance to CSF outflow was calculated as the absolute increase in intracranial pressure (interpolated over vasogenic waves) divided by the infusion rate (1.5 ml/min in most cases). The index of autoregulation was assessed as a correlation coefficient (moving time window of 5 min) between slow waves (with periods of 20 s to 2 min) in mean blood flow velocity and cerebral perfusion pressure.

RESULTS

The mean intracranial pressure increased during the test, from 6 mm Hg (standard deviation, 6 mm Hg) to 20 mm Hg (standard deviation, 10 mm Hg) (P < 0.0001). The index of autoregulation was significantly correlated with the resistance to CSF outflow (r = -0.41, P < 0.03), indicating better autoregulation with greater resistance to CSF outflow.

CONCLUSION

Patients presenting with ventricular dilation may exhibit either decreased (atrophy) or increased (normal-pressure hydrocephalus) resistance to CSF outflow. Increased resistance is correlated with preserved autoregulation. Patients with low resistance, suggesting brain atrophy, more often have disturbed autoregulation in the middle cerebral artery territory, as assessed by transcranial Doppler ultrasonography.

Functional magnetic resonance imaging before and after ventriculoperitoneal shunting for hydrocephalus--case report

A 70-year-old man with hydrocephalus was examined with functional magnetic resonance (fMR) imaging before and after ventriculoperitoneal shunting. Preoperatively, activation by right hand exercise revealed only a slight signal increase in the peri-rolandic area. However, 3 months after ventriculoperitoneal shunting, a significant signal increase was observed. fMR imaging may detect activity-related improvement of cerebral blood flow responses in patients with hydrocephalus after surgical treatment.

Normal pressure hydrocephalus and cerebral blood flow: a review

Normal pressure hydrocephalus is a neurological disease which poses both diagnostic and therapeutic problems for the clinician. The measurement and characterisation of cerebral blood flow has been proposed as a tool for resolving such problems as well as elucidating its pathophysiology. We review the results of studies in which this tool has been applied to normal pressure hydrocephalus patients and consider the merits of the techniques that have been utilised. Finally, consideration is given to feasible future studies and the methods that could be employed in the study of cerebral blood flow and metabolism in patients with normal pressure hydrocephalus.

Effects of ventriculoperitoneal shunt removal on cerebral oxygenation and brain compliance in chronic obstructive hydrocephalus

OBJECT

The pathophysiology of shunt malfunction has not been fully examined, probably because of the paucity of appropriate animal models. Using a canine model of chronic obstructive hydrocephalus, the effects of shunt placement and removal on physiological parameters were evaluated.

METHODS

Fifteen dogs, nine in which chronic hydrocephalus was induced and six controls, were used in the experiment. Thirteen weeks after the induction of hydrocephalus, intracranial pressure (ICP), tissue and cerebrospinal fluid O2 saturation, response to hyperventilation, and brain compliance at low (5-15 mm Hg) and high (15-25 mm Hg) pressures were measured (untreated stage). Following this procedure, ventriculoperitoneal shunts were implanted in the dogs suffering from hydrocephalus. Two weeks later, the same series of measurements were repeated (shunted stage), following which the shunt systems were removed. One week after shunt removal, the last measurements were obtained (shunt-removed stage). All dogs underwent magnetic resonance imaging four times: before induction of hydrocephalus and before each measurement. All dogs with hydrocephalus also had ventriculomegaly (1.42 +/- 0.89 ml before induction of hydrocephalus compared with 3.4 +/- 1.64 ml 13 weeks after induction, p = 0.0064). In dogs in the untreated hydrocephalus stage, ICP remained within the normal range (8.33 +/- 2.60 mm Hg)--although it was significantly higher than that in the control group (5 +/- 1.41 mm Hg, p = 0.014). Tissue O2 saturation in the dogs in the hydrocephalus group (26.1 +/- 5.33 mm Hg) was lower than that in the dogs in the control group (48.7 +/- 4.27 mm Hg, p < 0.0001). After the dogs underwent shunt placement, significant improvement was observed in their ICP (5.22 +/- 2.17 mm Hg, p = 0.012) and tissue O2 saturation (35.2 +/- 6.80 mm Hg, p = 0.0084). However, removal of the shunt reversed these improvements back to the preshunt status. Hyperventilation induced significant decreases in ICP and O2 saturation at every measurement time and induced a significant decrease in tissue O2 saturation during the shunted stage, but not during the untreated and shunt-removed stages. Brain compliance measured at high pressure demonstrated a significant gradual decrease at every measurement.

CONCLUSIONS

In chronic obstructive hydrocephalus, shunt placement improves ICP and cerebral oxygenation as well as the response to hyperventilation in the tissue. Shunt removal reverses these improvements back to levels present during the untreated stage. The decrease in brain compliance may be one of the factors responsible for symptoms in shunt malfunction.

Clinical features of late-onset idiopathic aqueductal stenosis

BACKGROUND

Although late-onset idiopathic aqueductal stenosis (LIAS) is considered a good indication for endoscopic third ventriculostomy (ETV), the characteristics of this clinical entity have seldom been reported in the magnetic resonance (MR) imaging era. The authors reviewed their patients with LIAS who were treated by ETV to confirm its clinical features and response to treatment.

METHODS

The study group was composed of 31 patients diagnosed with LIAS who were previously untreated. Both anatomic and cine phase-contrast MR studies were used to detect the obstruction of the aqueduct canal. The preoperative symptoms were statistically analyzed in relation to the age of the patients and the degree of preoperative ventriculomegaly.

RESULTS

The overall success rate of ETV was 83.9% with mean follow-up duration of 26.2 months. Only two patients had acute onset (within one month) without any predisposing chronic symptoms. The patients with chronic symptoms (longer than 6 months [n = 25]) can be divided into two major groups: a headache group (n = 12) and a normal pressure hydrocephalus (NPH)-symptom group (n = 11), Two patients had both headaches and NPH symptoms. The patients in the headache group were significantly younger and had smaller ventricles than the patients in the NPH group. With multivariate regression analysis, age independently affected the type of chronic symptoms.

CONCLUSIONS

LIAS typically presents with chronic onset, with younger patients tending to have headaches, and older patients tending to have NPH symptoms. ETV is considered the best surgical option, with more than an 80% success rate.