Idiopathic normal pressure hydrocephalus: new findings and thoughts on etiology

Global Neurocognitive and Frontal Functions Analysis and Precision Intrathecal Pressure Measurement to Settle the Diagnostic Dilemma of the Normal Pressure Hydrocephalus: A Preliminary Experience

INTRODUCTION

Normal-pressure hydrocephalus (NPH) is a common condition associated with a cognitive deterioration and possibly involving up to 9%-14% of all nursing home residents older than 65 years old. The purpose of the present paper is to introduce an inclusive study protocol aimed at increasing the diagnostic precision and follow-up accuracy.

METHODS

A total of 28 patients were operated on for NPH in our institution in the period ranging between January 2015 and December 2019. All the patients underwent magnetic resonance imaging of the brain with standard sequences, calculation of the Evans index and corpus callosum angle, and evaluations by means of Montreal Cognitive Assessment (MOCA), Mini-Mental State Examination, and Frontal Assessment Battery (FAB) neuropsychological tests preoperatively and at 1 and 6 months. A preoperative lumbar test infusion (LIT) with fine measurement of the intrathecal pressures at the beginning and at the end of the procedures was performed.

RESULTS

MOCA and FAB proved an overall improvement of the neurocognitive conditions at 1 month postoperatively. The mean pressure at the beginning of the LIT, was negatively associated with the neuropsychological outcome variables (Mini-Mental State Examination, FAB, and MOCA) in the 3 different evaluations, with FAB and MOCA at 6 months. We found a strong positive correlation between the Evans index as measured on the first magnetic resonance imaging scan both with the diastolic and systolic pressure at the beginning of the test.

CONCLUSIONS

Neuropsychological assessment, combined with LIT with intrathecal pressure managements aids the diagnostic process in patients affected by NPH. It allows standardizing in a rigorous fashion the follow-up evaluation of patients undergoing surgery for a ventriculoperitoneal shunt.

Measurement of CSF pulsation from EPI-based human fMRI

It is recently discovered that the glymphatic system and meningeal lymphatic system are the primary routes for the clearance of brain waste products. The CSF flow is part of these systems, facilitating the clearance procedure. Nonetheless, the relationship between CSF flow and brain functional activity has been underexplored. To investigate CSF dynamics and functional brain activity simultaneously, recent studies have proposed a CSF inflow index measured on edge slices (CSFedge) of echo-planar imaging (EPI) based functional magnetic resonance imaging (fMRI), however, it lacks the quantitative aspect of the CSF pulsation. We proposed a new method for quantifying CSF pulsation (CSFpulse) based on an interslice CSF pulsation model in the 4^th ventricle of EPI-based fMRI. The proposed CSFpulse successfully detected the higher CSF flow during the resting state than the typical task states (visual and motor) (p<.05), which is consistent with previous studies based on phase contrast (PC) MRI and CSF volume MRI, while it was not detected in CSFedge based indices or baseline CSF signals in various regions of interest (ROIs). Moreover, CSFpulse demonstrated dynamic functional changes in CSF pulsation: it decreased during the activation-on blocks while it increased during the activation-off blocks. CSFpulse significantly correlated with stroke volume measured using PC MRI, a standard method for CSF pulsation quantification, under the same functional state, while CSFedge based indices or CSF ROIs showed no correlation with the PC MRI stroke volume. Lastly, the correlation of CSFpulse with global BOLD was weaker than that of CSFedge, suggesting that CSFpulse may reflect distinct CSF physiological information that is less affected by global BOLD effects. Based on these results, the proposed CSFpulse provides CSF pulsatility information more accurately in a quantitative manner than CSFedge based indices from the recent CSF studies or the conventional ROI-based analysis. In addition to the high correlation with PC MRI, CSFpulse is much faster than PC MRI and provides information of functional brain activations simultaneously, advantageous over PC MRI or CSF volume MRI. Accordingly, the suggested CSFpulse can be used for investigating intra-subject functional changes in BOLD and CSF pulsation simultaneously and inter-subject CSF pulsation variations based on conventional EPI-based fMRI, which warrants further investigation.

Evaluation of cerebrospinal fluid flow dynamic changes in patients with idiopathic intracranial hypertension using phase contrast cine MR imaging

Background

Idiopathic intracranial hypertension (IIH) mainly affects overweight women in the middle age period. The pathophysiology of IIH stays unclear, but suggested mechanisms include excess CSF production, reduced CSF absorption, increased brain water content, and increased cerebral venous pressure

Objectives

To assess the cerebrospinal fluid (CSF) flow dynamic changes in aqueduct of Sylvius in patients of idiopathic intracranial hypertension (IIH) with new MRI technique: phase contrast cine MRI (PCC-MRI).

Methods

Thirty patients diagnosed with idiopathic intracranial hypertension were divided into 3 groups according to treatment options (no treatment, medical treatment, and medical treatment with repeated lumbar tapping). CSF flow data were evaluated by phase contrast cine MRI.

Results

PCC-MRI parameters were significantly higher in group who was on medical treatment (group II) than other groups. The sensitivity of PCC MRI parameters ranged from 56.7 (stroke volume (SV) and mean flow (MF)) to 83.3% (peak systolic velocity (PSV)). A statistically significant difference was found for the mean flow value (p 0.039) between the control group and IIH patients.

Conclusion

The most specific CSF flowmetry parameter detected to help diagnosis of IIH is mean flow especially among early discovered patients. PCC MRI can be used as non-invasive technique for diagnosis of IIH and treatment follow-up.

Magnetic resonance elastography to estimate brain stiffness: Measurement reproducibility and its estimate in pseudotumor cerebri patients

This study determines the reproducibility of magnetic resonance elastography (MRE) derived brain stiffness in normal volunteers and compares it against pseudotumor patients before and after lumbar puncture (LP). MRE was performed on 10 normal volunteers for reproducibility and 14 pseudotumor patients before and after LP. During LP, opening and closing cerebrospinal fluid (CSF) pressures were recorded before and after removal of CSF and correlated to brain stiffness. Stiffness reproducibility was observed (r > 0.78; p < 0.008). Whole brain opening LP stiffness was significantly (p = 0.04) higher than normals, but no significant difference (p = 0.11) in closing LP measurements. No significant correlation was observed between opening and closing pressure and brain stiffness.

Quantitative analysis of cerebrospinal fluid dynamics at phase contrast cine-MRI: predictivity of neurosurgical "Shunt" responsiveness in patients with idiopathic normal pressure hydrocephalus

BACKGROUND

Aqueductal stroke volume (ACSV) measured by phase-contrast cine (PCC)-MRI has been proposed with controversy as a tool for the selection of patients with normal pressure hydrocephalus (NPH) as candidates for shunt-surgery. The aim of this study was to assess if PCC-MRI scan measurements of ACSV could select properly these patients.

METHODS

We retrospectively reviewed charts and MRI of 38 shunted patients (72.16±6.16 years). ACSV measurements were performed 7-30 days before shunt and at the first and sixth months after surgery. Normally distributed variables were compared in the two groups (improved/unimproved) by t-test for baseline values and with repeated measures analysis of variance.

RESULTS

Twenty-six patients (68,4%) improved after VPS (mean time of symptom onset was 8.15±7.19 months). Mean preoperative ACSV value was 271.85±143.03, which decreased by 21.6% (mean 213±125.14) at the first month and 40.3% sixth months after VPS (mean 162.15±91.5). Twelve patients (31.6%) did not improve (mean time of symptom onset was 29±5.62 months). Mean preoperative ACSV value was 79.83±31.24, decreased to 8.7% (mean 72.83±28.66) at first month after VPS. 21.2% (mean 62.83±31.12) after six months. We found statistical difference between preoperative ACSV of improved and unimproved patients (P<0.01), onset time of symptoms (P<0.01) and the changes in ACSV after one and six months in both groups (P<0.001).

CONCLUSIONS

ACSV is useful to stratify patients with NPH after surgery (improved /not improved) suggesting to proceed with serial ACSV measurements before deciding treatment.

Negative-Pressure Hydrocephalus: A Case Report on Successful Treatment Under Intracranial Pressure Monitoring with Bilateral Ventriculoperitoneal Shunts

BACKGROUND

Negative-pressure hydrocephalus (NegPH), a very rare condition of unknown etiology and optimal treatment, usually presents postneurosurgery with clinical and imaging features of hydrocephalus, but with negative cerebrospinal fluid pressure.

CASE DESCRIPTION

We describe a NegPH case of -3 mm Hg intracranial pressure that was successfully treated to achieve 5 mm Hg under continuous intracranial pressure monitoring with horizontal positioning, head down and legs elevated to 10°-15°, neck wrapping for controlled venous drainage, chest and abdomen bandages, infusion of 5% dextrose fluid to lower plasma osmolarity (Na⁺, 130-135 mmol/L), daily cerebrospinal fluid drainage >200 mL, and arterial blood gas partial pressure of carbon dioxide >40 mm Hg.

Normal pressure hydrocephalus as a failure of ICP homeostasis mechanism: the hidden role of Monro-Kellie doctrine in the genesis of NPH

OBJECTIVE

The theme of this paper is to outline that the genesis of normal pressure hydrocephalus (NPH) is governed by the intracranial pressure (ICP) homeostatic principle. The development of this new concept is based mainly on rethinking the well-known Monro-Kellie doctrine in the way that ICP homeostasis mechanism is not only a mechanism that works to prevent pathologically high ICP but also a mechanism that aims to protect from pathologically low ICP.

METHODS

The NPH-related literatures are reviewed and reinterpreted to generate a new paradigm for the cascade of pathophysiological events that leads to the genesis NPH, as well as the mechanism of clinical beneficial effects and complications of the shunting procedure.

RESULTS

According to this new paradigm, the suboptimal cerebral perfusion that is associated with the impairment of the cerebral autoregulation is the initial step in the genesis of NPH. When the overall volume of blood that circulates intracranially is diminished, a chronic low ICP with episodes of pathologically low ICP occurs. Since the cranial vault is not collapsible, those episodes of low ICP are compensated by the accumulation of cerebrospinal fluid (CSF) to keep the ICP in normal ideal range. The impairment of brain toxin-flushing mechanism because of CSF pooling combined with the already-established suboptimal cerebral perfusion leads to functional disinhibition of the cerebral cortex.

CONCLUSION

Recognizing the importance of ICP homeostatic mechanisms in the genesis of the NPH is a simple yet novel view that could change the way we look at NP and can give a basic and fundamental theoretical frame work to achieve better understanding of NPH.

"Flow comp off": An easy technique to confirm CSF flow within syrinx and aqueduct

Flow compensation, a gradient pulse used for artifact reduction, often used to suppress cerebrospinal fluid (CSF) flow artifacts in spinal magnetic resonance imaging (MRI), can be switched off to make the CSF flow voids within syrinx (syringomyelia) and within aqueduct [normal pressure hydrocephalus (NPH)] more obvious (thus confirming CSF flow). It is a simple method which does not require much time or expertise.

Venous hemodynamics in neurological disorders: an analytical review with hydrodynamic analysis

Venous abnormalities contribute to the pathophysiology of several neurological conditions. This paper reviews the literature regarding venous abnormalities in multiple sclerosis (MS), leukoaraiosis, and normal-pressure hydrocephalus (NPH). The review is supplemented with hydrodynamic analysis to assess the effects on cerebrospinal fluid (CSF) dynamics and cerebral blood flow (CBF) of venous hypertension in general, and chronic cerebrospinal venous insufficiency (CCSVI) in particular.CCSVI-like venous anomalies seem unlikely to account for reduced CBF in patients with MS, thus other mechanisms must be at work, which increase the hydraulic resistance of the cerebral vascular bed in MS. Similarly, hydrodynamic changes appear to be responsible for reduced CBF in leukoaraiosis. The hydrodynamic properties of the periventricular veins make these vessels particularly vulnerable to ischemia and plaque formation.Venous hypertension in the dural sinuses can alter intracranial compliance. Consequently, venous hypertension may change the CSF dynamics, affecting the intracranial windkessel mechanism. MS and NPH appear to share some similar characteristics, with both conditions exhibiting increased CSF pulsatility in the aqueduct of Sylvius.CCSVI appears to be a real phenomenon associated with MS, which causes venous hypertension in the dural sinuses. However, the role of CCSVI in the pathophysiology of MS remains unclear.

Proton MR spectroscopy and white matter hyperintensities in idiopathic normal pressure hydrocephalus and other dementias

The differentiation of idiopathic normal-pressure hydrocephalus (INPH) from other types of dementia is a clinical challenge. The aim of this prospective study was to evaluate the role of proton MR spectroscopy (MRS) and white matter hyperintensities (WMH) in the diagnosis of INPH, predicting response to therapy and differentiating INPH from other dementias. The study included 18 patients with INPH (Group 1), 11 patients with other types of dementia (Group 2) and 20 control patients (Group 3). The value of WMH scores and MRS findings in diagnosis, evaluation of response to therapy and in the differentiation of INPH from other dementias was statistically evaluated. The level of statistical significance was set at p<0.05 (Kruskal-Wallis and Mann-Whitney U-test). In both Groups 1 and 2, N-acetylaspartate (NAA)/choline-NAA/creatine ratios were significantly less than in the control group (p<0.05). The WMH and MRS findings of Groups 1 and 2 demonstrated no statistically significant correlation (p>0.05). No correlation was found between the outcome of shunt operations and WMH and MRS findings (p>0.05). In conclusion, neither WMH nor MRS were useful in differentiating INPH from other types of dementia. WMH and MRS showed no additional benefit in identifying INPH patients who will better respond to shunt therapy.

The efficiency of PC-MRI in diagnosis of normal pressure hydrocephalus and prediction of shunt response

RATIONALE AND OBJECTIVES

In this prospective study, we aimed to reveal the efficiency of phase-contrast magnetic resonance imaging (PC-MRI) in the diagnosis of idiopathic normal pressure hydrocephalus (INPH) and prediction of shunt response.

MATERIALS AND METHODS

The study group consisted of 43 patients with INPH diagnosis and 15 asymptomatic age-matched controls. PC-MRI studies were applied on cerebral aqueduct and superior sagittal sinus (SSS) in all the cases.

RESULTS

The maximum and mean cerebrospinal fluid (CSF) flow velocities were significantly higher in the INPH patients compared with the controls (P < .05). CSF stroke volume (43.2 + or - 63.8 microL) and output/min (3921 + or - 5668 microL) were remarkably higher in the NPH group compared with the control group (3.9 + or - 3.9 microL, 439 + or - 487 microL, respectively) (P < .05). Maximum and mean venous velocity values of the INPH patients (maximum, 19.2 + or - 4.3 cm/s; mean, 16 + or - 3.7 cm/s), were lower than those of the control group (maximum, 21.8 + or - 4.6 cm/s; mean, 18.9 + or - 3.9 cm/s) (P < .05). Stroke volume and venous output/min values of INPH patients in SSS, were significantly lower than those of the control group (P < .001, P = .007, respectively). The response of INPH patients against shunt treatment showed no statistical correlation with any of the PC-MRI parameters (P > .05).

CONCLUSION

The measurement of CSF venous flow velocities with PC-MRI is a noninvasive test that benefits INPH diagnosis, but remains inadequate in prediction of response against shunt treatment.

Idiopathic Normal Pressure Hydrocephalus: Correlating Magnetic Resonance Imaging Biomarkers with Clinical Response

Idiopathic Normal Pressure Hydrocephalus (NPH) is a debilitating condition of the elderly. The patient is typically “wet, wobbly and wonky”, to different degrees of the triad. The diagnosis is supported by the radiologic finding of dilated ventricles, determined by an elevated Evan’s Index (EI) without a demonstrable cause. Patients with newly diagnosed NPH typically respond to ventriculo-peritoneal shunting (VPS). NPH-related dementia is possibly the only surgically reversible dementia. An elevated cerebrospinal fluid (CSF) flow rate (FR) is associated with a positive response to shunting. However, post-shunting EI and FRs are unpredictable. Of late, intracranial apparent diffusion coefficient (ADC) quantification via Diffusion Weighted Imaging (DWI) has been emerging as a possible marker in NPH diagnosis. A local study, conducted on a national level, to study the relationship of EI, FR and ADC to pre- and post-shunt clinical measurements has just ended. This review seeks to reconcile the current thinking of NPH, magnetic resonance imaging (MRI) quantification and clinical evaluation, and in the process shed some light on major pathophysiological determinants of the disease.