Pathogenesis of idiopathic Normal Pressure Hydrocephalus: A review of knowledge

A bibliometric analysis and visualization of normal pressure hydrocephalus

Background

Normal pressure hydrocephalus (NPH) has drawn an increasing amount of attention over the last 20 years. At present, there is a shortage of intuitive analysis on the trends in development, key contributors, and research hotspots topics in the NPH field. This study aims to analyze the evolution of NPH research, evaluate publications both qualitatively and quantitatively, and summarize the current research hotspots.

Methods

A bibliometric analysis was conducted on data retrieved from the Web of Science Core Collection (WoSCC) database between 2003 and 2023. Quantitative assessments were conducted using bibliometric analysis tools such as VOSviewer and CiteSpace software.

Results

A total of 2,248 articles published between 2003 and 2023 were retrieved. During this period, the number of publications steadily increased. The United States was the largest contributor. The University of Gothenburg led among institutions conducting relevant research. Eide P. K. was the most prolific author. The Journal of Neurosurgery is the leading journal on NPH. According to the analysis of the co-occurrence of keywords and co-cited references, the primary research directions identified were pathophysiology, precise diagnosis, and individualized treatment. Recent research hotspots have mainly focused on epidemiology, the glymphatic system, and CSF biomarkers.

Conclusion

The comprehensive bibliometric analysis of NPH offers insights into the main research directions, highlights key countries, contributors, and journals, and identifies significant research hotspots. This information serves as a valuable reference for scholars to further study NPH.

Pathogenesis and management of low-pressure hydrocephalus: A narrative review

Patients diagnosed with low-pressure hydrocephalus typically present with enlarged ventricles and unusually low intracranial pressure, often measuring below 5 cmH2O or even below atmospheric pressure. This atypical presentation often leads to low recognition and diagnostic rates. The development of low-pressure hydrocephalus is believed to be associated with a decrease in the viscoelasticity of brain tissue or separation between the ventricular and subarachnoid spaces. Risk factors for low-pressure hydrocephalus include subarachnoid hemorrhage, aqueduct stenosis, prior cranial radiotherapy， ventricular shunting, and cerebrospinal fluid leaks. For potential low-pressure hydrocephalus, diagnostic criteria include neurological symptoms related to hydrocephalus, an Evans index >0.3 on imaging, ICP ≤ 5 cm H2O, symptom improvement with negative pressure drainage, and exclusion of ventriculomegaly caused by neurodegenerative diseases. The pathogenesis and pathophysiological features of low-pressure hydrocephalus differ significantly from other types of hydrocephalus, making it challenging to restore normal ventricular morphology through conventional drainage methods. The primary treatment options for low-pressure hydrocephalus involve negative pressure drainage and third ventriculostomy. With appropriate treatment, most patients can regain their previous neurological function. However, in most cases, permanent shunt surgery is still necessary. Low-pressure hydrocephalus is a rare condition with a high rate of underdiagnosis and mortality. Early identification and appropriate intervention are crucial in reducing complications and improving prognosis.

Loss of Katnal2 leads to ependymal ciliary hyperfunction and autism-related phenotypes in mice

Autism spectrum disorders (ASD) frequently accompany macrocephaly, which often involves hydrocephalic enlargement of brain ventricles. Katnal2 is a microtubule-regulatory protein strongly linked to ASD, but it remains unclear whether Katnal2 knockout (KO) in mice leads to microtubule- and ASD-related molecular, synaptic, brain, and behavioral phenotypes. We found that Katnal2-KO mice display ASD-like social communication deficits and age-dependent progressive ventricular enlargements. The latter involves increased length and beating frequency of motile cilia on ependymal cells lining ventricles. Katnal2-KO hippocampal neurons surrounded by enlarged lateral ventricles show progressive synaptic deficits that correlate with ASD-like transcriptomic changes involving synaptic gene down-regulation. Importantly, early postnatal Katnal2 re-expression prevents ciliary, ventricular, and behavioral phenotypes in Katnal2-KO adults, suggesting a causal relationship and a potential treatment. Therefore, Katnal2 negatively regulates ependymal ciliary function and its deletion in mice leads to ependymal ciliary hyperfunction and hydrocephalus accompanying ASD-related behavioral, synaptic, and transcriptomic changes.

Application of LRG mechanism in normal pressure hydrocephalus

Normal pressure hydrocephalus (NPH) is a prevalent type of hydrocephalus, including secondary normal pressure hydrocephalus (SNPH) and idiopathic normal pressure hydrocephalus (INPH). However, its clinical diagnosis and pathological mechanism are still unclear. Leucine-rich α-2 glycoprotein (LRG) is involved in various human diseases, including cancer, diabetes, cardiovascular disease, and nervous system diseases. Now the physiological mechanism of LRG is still being explored. According to the current research results on LRG, we found that the agency of LRG has much to do with the known pathological process of NPH. This review focuses on analyzing the LRG signaling pathways and the pathological mechanism of NPH. According to the collected literature evidence, we speculated that LRG probably be involved in the pathological process of NPH. Finally, based on the mechanism of LRG and NPH, we also summarized the evidence of molecular targeted therapies for future research and clinical application.

Positive association between omega-3/6 polyunsaturated fatty acids and idiopathic normal pressure hydrocephalus: a mendelian randomization study

Background: Idiopathic normal pressure hydrocephalus (iNPH) is a common disease among the elderly, which brings great harm to the health of patients and imposes a huge economic burden on the healthcare system. Research has shown that it is possible to prevent iNPH through nutritional and dietary interventions. Intake of omega-3 and omega-6 polyunsaturated fatty acids (PUFAs) can reduce the risk of many diseases. In this study, we aimed to explore the association between omega-3/6 PUFAs and iNPH. Methods: We conducted a two-sample Mendelian randomization (MR) study using summary data from publicly available genome-wide association studies (GWAS) to evaluate the potential impact of omega-3 and omega-6 PUFAs on the risk of iNPH in European populations. Inverse variance weighting was used as the main method for MR analysis, with Wald ratio, weighted median, MR-Egger, simple mode, and weighted mode as supplementary methods. In addition, we performed a series of instrument variable strength evaluations and sensitivity analyses to test the reliability of the study results. Finally, we also conducted a linkage disequilibrium score regression (LDSC) analysis to assess the genetic correlation and distinguish between causal associations and shared genetic variants between PUFAs and iNPH. Results: One SD increase in genetically predicted levels of total omega-3 PUFAs (OR: 0.748; 95% CI: 0.597-0.937; p = 0.012; IVW), DHA (OR: 0.709; 95% CI: 0.532-0.945; p = 0.019; IVW), ALA (OR: 0.001; 95% CI: 1.17E-06-0.423; p = 0.026; Wald ratio), and DHA (OR: 0.709; 95% CI: 0.532-0.945; p = 0.019; IVW) were associated with a reduced iNPH risk. LDSC did not reveal any significant genetic correlations. Conclusion: Higher genetically predicted levels of total omega-3 PUFAs, ALA, DHA, and DPA are associated with a reduced risk of iNPH. These findings have important implications for preventing iNPH and future nutritional guidance.

The Efficacy of Endoscopic Third Ventriculostomy for Idiopathic Normal Pressure Hydrocephalus

Recently, intervention with endoscopic third ventriculostomy (ETV) for patients with idiopathic normal pressure hydrocephalus (iNPH) has emerged as a potential minimally invasive alternative to traditional treatments (ventriculoperitoneal shunting). The clinical response to these interventions is variable and unclear. The objective of this review was to assess the efficacy of endoscopic third ventriculostomy in treating patients with iNPH. A systematic review of PubMed, Web of Science, and Google Scholar was conducted using search terms relevant to ETV and iNPH. Included studies met consistent, predetermined diagnostic criteria for iNPH, implemented ETV in subjects greater than 40 years of age, and assessed all 3 components of Hakim's triad (gait impairment, dementia, and incontinence). Data extraction included dichotomization of successful ETV clinical outcomes and a subgroup meta-analysis of ETV success rates across binarized age groups. Meta-analysis was conducted using a Mantel-Haenszel fixed-effects model. The outcomes presented include generalized ETV success rates across all 12 studies. Age-specific individual data was measured with odds ratios, with a pooled statistic measured using the Mantel-Haenszel test. Overall, 2294 studies were identified in this search, of which 12 were selected for inclusion in this systematic review. Of these, 3 studies were utilized for age-specific meta-analyses. Preliminary synthesis of ETV clinical outcomes across all 12 studies revealed a success rate of 60.2%. Additionally, meta-analysis revealed that iNPH patients younger than or equal to 65 years of age were significantly more likely to respond successfully to ETV intervention. Heterogeneity was inconsequential in this analysis.

Gait Analysis in Idiopathic Normal Pressure Hydrocephalus: A Meta-Analysis

Background

Gait analysis objectively quantifies gait impairment in idiopathic normal pressure hydrocephalus (iNPH), may improve diagnosis and evaluation for surgical candidacy.

Objectives

This meta-analysis aims to understand which objective gait parameters improve after tap-test (TT) and CSF shunt surgery (CSS), also comparing responders (R) with non-responders (NR) and to assess if gait restores within the range of healthy controls after procedures.

Methods

Studies enrolling iNPH with at least one instrumented gait measure were selected. Three time points of gait assessment were defined: PRE, POST-TT, and POST-CSS. Gait velocity, cadence, step length, stride length, and double limb support time were evaluated. Patients were categorized based on responsiveness to CSF diversion procedures.

Results

Seventeen studies including 527 patients were selected. iNPH improved significantly in almost all gait parameters POST-TT, and to a greater extent POST-CSS. Gait parameters consistently discriminated iNPH from healthy controls. Despite the aforementioned improvements, iNPH's gait did not completely normalize after CSF diversion procedures. Meta-regression analysis also revealed that TT's effect on gait velocity plateaus after 24-48 hr and returns to baseline in 90-100 hr.

Conclusions

Gait analysis is a reliable quantitative instrument to assess gait impairment in iNPH, demarking a net differentiation from healthy controls, according to the notion that the iNPH CSF dynamic alteration also leads to an irreversible damage. Specific gait parameters improve among TT-R, providing an opportunity to select patients that will respond to CSS. Future studies validating a standardized reporting method including criteria of responsiveness, specific gait parameters, and timeframe of assessment are needed.

The PUMCH Evaluation System of Idiopathic Normal Pressure Hydrocephalus and Clinical Practice

OBJECTIVE

Differentiating idiopathic normal pressure hydrocephalus (iNPH) from other neurodegenerative diseases is challenging. Only a portion of the patients clinically suspected of iNPH would respond to surgical intervention. A cerebrospinal fluid (CSF) tap test is usually used to predict surgery outcomes and hence aid clinical decision-making, but the workup varies. We introduce the CSF tap test conducted at our center and examine its power by analyzing data from a series of iNPH cases that underwent shunt placement. We analyze common features in the past medical history of our patients and investigate whether they are related to the etiology of iNPH.

METHODS

Data from 20 patients who were positive in the tap tests preoperatively and received ventriculoperitoneal shunting (VPS) were retrospectively analyzed. Preoperative and postoperative performance data were analyzed. History of any underlying medical conditions was taken into consideration. Patients with negative tap test results of the same period were also followed up.

RESULTS

We performed VPS placement in 20 NPH patients from October 2019 to February 2022. Of these, 90% exhibited improvement in at least 1 of the clinical triad, proving the predictive power of the Peking Union Medical College Hospital test workflow. The underlying conditions like hypertension, diabetes and insufficiency in cerebral blood supply were also found to be associated with the onset of NPH.

CONCLUSION

Our evaluation system is a valid tool for NPH assessment and can guide clinical decision-making. Comorbidities should be taken into consideration as they contribute to the pathogenesis and progression of NPH. Better identification of potential iNPH patients will lower the burden exerted on the family and the aging society.

Outcomes of the 2019 hydrocephalus association workshop, "Driving common pathways: extending insights from posthemorrhagic hydrocephalus"

The Hydrocephalus Association (HA) workshop, Driving Common Pathways: Extending Insights from Posthemorrhagic Hydrocephalus, was held on November 4 and 5, 2019 at Washington University in St. Louis. The workshop brought together a diverse group of basic, translational, and clinical scientists conducting research on multiple hydrocephalus etiologies with select outside researchers. The main goals of the workshop were to explore areas of potential overlap between hydrocephalus etiologies and identify drug targets that could positively impact various forms of hydrocephalus. This report details the major themes of the workshop and the research presented on three cell types that are targets for new hydrocephalus interventions: choroid plexus epithelial cells, ventricular ependymal cells, and immune cells (macrophages and microglia).

The choroid plexus: a missing link in our understanding of brain development and function

Studies of the choroid plexus lag behind those of the more widely known blood-brain barrier, despite a much longer history. This review has two overall aims. The first is to outline long-standing areas of research where there are unanswered questions, such as control of cerebrospinal fluid (CSF) secretion and blood flow. The second aim is to review research over the past 10 years where the focus has shifted to the idea that there are choroid plexuses located in each of the brain's ventricles that make specific contributions to brain development and function through molecules they generate for delivery via the CSF. These factors appear to be particularly important for aspects of normal brain growth. Most research carried out during the twentieth century dealt with the choroid plexus, a brain barrier interface making critical contributions to the composition and stability of the brain's internal environment throughout life. More recent research in the twenty-first century has shown the importance of choroid plexus-generated CSF in neurogenesis, influence of sex and other hormones on choroid plexus function, and choroid plexus involvement in circadian rhythms and sleep. The advancement of technologies to facilitate delivery of brain-specific therapies via the CSF to treat neurological disorders is a rapidly growing area of research. Conversely, understanding the basic mechanisms and implications of how maternal drug exposure during pregnancy impacts the developing brain represents another key area of research.

Endoscopic third ventriculostomy compared to ventriculoperitoneal shunt as treatment for idiopathic normal pressure hydrocephalus: a systematic review and meta-analysis

BACKGROUND

The accepted treatment for idiopathic normal pressure hydrocephalus (iNPH) is the insertion of a ventriculoperitoneal shunt (VPS). Recently, some studies examined endoscopic third ventriculostomy (ETV) for the treatment of iNPH with controversial results. The aim of this systematic review and meta-analysis was to compare ETV to VPS regarding complications and outcome for the treatment of iNPH.

METHODS

We searched Medline, Embase and Scopus. Due to the scarcity of data, we did not include only randomized controlled trials, but also retro- and prospective studies. The primary outcome was failure of cerebrospinal fluid diversion method. Secondary endpoints were clinical postoperative improvement rate, morbidity and mortality.

RESULTS

Out of 311 screened studies, three were included in the quantitative analysis including one RCT and two retrospective cohort studies. No statistically significant difference concerning failure rate of CSF diversion method (ETV 27.5% vs. VPS 33.2%, RR 1.19, 95% CI [0.69-2.04], p = 0.52) or postoperative improvement was found (68% for ETV vs. 72.8% for VPS, RR 0.81, 95% CI [0.57-1.16], p = 0.26). ETV showed a significantly lower complication rate compared to VPS (7.5% vs. 51.1%, RR 0.25, 95% CI [0.08-0.76], p = 0.02).

CONCLUSION

ETV and VPS did not differ significantly regarding their failure rate for iNPH, while ETV showed a significantly lower complication rate than VPS. However, the data available is scarce with only one RCT investigating this important matter. Further well-designed trials are necessary to investigate the clinical outcome of ETV in iNPH.

TRIAL REGISTRATION NUMBER

PROSPERO (ID: CRD42020199173).

Research Evidence of the Role of the Glymphatic System and Its Potential Pharmacological Modulation in Neurodegenerative Diseases

The glymphatic system is a unique pathway that utilises end-feet Aquaporin 4 (AQP4) channels within perivascular astrocytes, which is believed to cause cerebrospinal fluid (CSF) inflow into perivascular space (PVS), providing nutrients and waste disposal of the brain parenchyma. It is theorised that the bulk flow of CSF within the PVS removes waste products, soluble proteins, and products of metabolic activity, such as amyloid-β (Aβ). In the experimental model, the glymphatic system is selectively active during slow-wave sleep, and its activity is affected by both sleep dysfunction and deprivation. Dysfunction of the glymphatic system has been proposed as a potential key driver of neurodegeneration. This hypothesis is indirectly supported by the close relationship between neurodegenerative diseases and sleep alterations, frequently occurring years before the clinical diagnosis. Therefore, a detailed characterisation of the function of the glymphatic system in human physiology and disease would shed light on its early stage pathophysiology. The study of the glymphatic system is also critical to identifying means for its pharmacological modulation, which may have the potential for disease modification. This review will critically outline the primary evidence from literature about the dysfunction of the glymphatic system in neurodegeneration and discuss the rationale and current knowledge about pharmacological modulation of the glymphatic system in the animal model and its potential clinical applications in human clinical trials.

Impact of Subjective Evaluations in Predicting Response to Ventriculoperitoneal Shunt for Idiopathic Normal Pressure Hydrocephalus

BACKGROUND

Cerebrospinal fluid tap test is a common procedure to predict the efficacy of ventriculoperitoneal shunt for idiopathic normal pressure hydrocephalus. Objective tests after cerebrospinal fluid tap test are used to establish the surgical indication, but subjective improvements may also be important in selection of surgical candidates. The aim of this study was to evaluate surgical outcomes of patients with ventriculoperitoneal shunt for idiopathic normal pressure hydrocephalus, comparing patients showing objective improvement with patients improving only on subjective assessments.

METHODS

In this retrospective analysis, patients were divided into 2 groups: group 1 included patients with improvement on objective evaluation after cerebrospinal fluid tap test; group 2 included patients who showed only subjective improvement. The surgical outcomes of the 2 groups were compared.

RESULTS

Of 28 included patients, 17 were objective responders (group 1), and 11 were subjective responders (group 2). Clinical and radiological characteristics were similar. The only significant difference was the baseline Berg Balance Scale, which was lower in objective responders (P = 0.0015). At 3 months after surgery and at last follow-up, there was no difference in surgical outcomes between the 2 groups. However, in the group of subjective responders, a continuous improvement for incontinence and gait was more frequently observed (P = 0.04 and P < 0.001, respectively).

CONCLUSIONS

Surgical outcomes after ventriculoperitoneal shunt were similar between the 2 groups, with a more favorable trend in terms of symptom improvement for subjective responders. Subjective assessment seems to be an important factor to consider in preoperative evaluation.

Plasma Neurofilament Light Chain and Clinical Diagnosis in Frontotemporal Dementia Syndromes

Background: Frontotemporal dementia (FTD) syndromes, mimics, phenocopy (phFTD), and slowly progressive behavioral variant FTD (bvFTD) can be difficult to distinguish clinically. Biomarkers such as neurofilament light chain (NfL) may be helpful. Objective: To study plasma NfL levels in people with FTD syndromes and determine if plasma NfL can distinguish between FTD syndromes and phFTD. Methods: Plasma NfL levels were estimated using both Simoa ® Quanterix HD-X™ and SR-X™ machines grouped via final diagnosis after investigation and review. Results: Fifty participants were studied: bvFTD = 20, semantic variant FTD (svFTD) = 11, non-fluent variant FTD (nfvFTD) = 9, FTD with motor neuron disease (MND) = 4, phFTD = 2, slow progressors = 3, FTD mimic = 1, mean age 67.2 (SD 8.4) years. NfL levels were significantly higher in the FTD group compared to phenocopy group (p = 0.003). Median NfL (IQR) pg/mL was comparable in the FTD syndromes: bvFTD 41.10 (50.72), svFTD 44.38 (16.61), and nfvFTD 42.61 (22.93), highest in FTD with MND 79.67 (45.32) and lowest in both phFTD 13.99 (0.79) and slow progressors 17.97 (3.62). Conclusion: Plasma NfL appears to differentiate FTD syndromes and mimics. However, a lower NfL may predict a slower, but not necessarily lack of, neurodegeneration and therefore appears limited distinguishing slow progressors from FTD phenocopies. Larger numbers of patients from all clinical groups are required to strengthen diagnostic utility.

The need for an institution-specific normal pressure hydrocephalus management protocol

Background

Despite the publication of international guidelines, the management of normal pressure hydrocephalus (NPH) varies due to clinician preference and varying clinical evidence. An audit was performed to review the current pathways used in clinical practice with the aim of formulating an institution-specific protocol to optimize and standardize care.

Methods

An internal audit was performed on the management of patients with NPH who presented to the Princess Alexandra Hospital, Brisbane between January 2016 and February 2019.

Results

Forty-one patients were included in the study. Lumbar puncture (LP) was the main diagnostic test used (63.4%). About 14.6% underwent lumbar drain (LD) insertion instead. About 12.2% did not undergo either LP or LD before definitive treatment. Only 60% of all patients underwent ventriculoperitoneal shunt insertion. Overall, five treatment pathways were noted. LP + VP shunt showed the greatest average improvement in Montreal Cognitive Assessment (MoCA) or Mini-Mental State Examination (MMSE) (+3.8 ± 3.18), followed by LD + VP shunt (+3.25 ± 3.52) and sole treatment with LP (+1.83 ± 1.18). Both pre and post intervention assessment of gait and cognition were only performed in 31% and 48.8% of patients, respectively. Four types of cognitive assessment were used (MOCA 46.4%, MMSE 46.4%, Rowland Universal Dementia Assessment Scale 3.6%, and Addenbrooke's Cognitive Examination-III 3.6%). MoCA showed greater cognition improvement (2.07) compared to MMSE (1.3) post intervention. There was no consistent objective gait assessment test used.

Conclusion

The multiple NPH treatment pathways, low rate of pre and post objective symptom assessment, and lack of standardized gait and cognitive assessment tests demonstrate a clear need for an institution-specific NPH management protocol to standardize diagnostic workup, definitive management, and allied health assessment.

Dual-Task Performance in Older Adults With and Without Idiopathic Normal Pressure Hydrocephalus

Two of the main features of idiopathic normal pressure hydrocephalus (iNPH) are disturbed gait and cognition. These features are typically investigated separately, but here we combined walking with a cognitive task to investigate if older adults with iNPH were more susceptible to dual-task interference on walking than those without iNPH. In total, 95 individuals from the general population participated in our study. Of these, 20 were classified as Possible iNPH (median [interquartile range, IQR] 80 years [75–82.5]) and 75 as Unlikely iNPH (74 years [72–78]). Conversation, 10-m walking, semantic and phonemic verbal fluency were performed either combined or independently. “Stopping walking while talking” was noted. Pairwise comparisons and multiple logistic regression analyses were used. We found that the Possible iNPH group was older, stopped walking more frequently during the conversation, and had a slower single-task pace. The dual-task pace was slower for both groups. Only single-task walking pace could predict Possible iNPH when adjusted for age. We could establish a dual-task cost on gait performance in this sample of older adults from the general population, but the cost was not exclusive for individuals with Possible iNPH. To further assess the value of dual-task testing in iNPH, including observations of stopping walking while talking, a study of a clinical iNPH material with more severe symptoms would be valuable.

Open-aqueduct LOVA, LIAS, iNPH: a comparative clinical-radiological study exploring the "grey zone" between different forms of chronic adulthood hydrocephalus

Purpose

The definition of chronic adult hydrocephalus encompasses different pathological entities with overlapping characteristics, including long-standing overt ventriculomegaly in adults (LOVA), late-onset idiopathic aqueductal stenosis (LIAS) and idiopathic normal pressure hydrocephalus (iNPH). The aim of our study was to identify preoperative clinical and radiological features peculiar of these diseases providing some pathophysiology inferences on these forms of hydrocephalus.

Methods

Clinical and radiological preoperative records, type of surgical treatment and clinical outcome of patients with chronic adult hydrocephalus who were surgically treated between 2013 and 2019 were retrospectively reviewed. Univariate and multivariate analyses were performed to evaluate the contribution of each variable to the differential diagnosis.

Results

In total, 105 patients were included: 18 with LOVA, 23 with LIAS and 64 with iNPH. On multivariate analysis, an enlarged cisterna magna and a more severe ventriculomegaly were associated with the diagnosis of LOVA, while an older age and DESH with iNPH. LIAS patients tend to have an higher prevalence of raised ICP symptoms. Based on that, a clinical and radiological scoring system was developed to distinguish between iNPH and no iNPH cases. A precise cut-off value with a sensitivity of 95.1% and a specificity of 90.6% was identified.

Conclusions

LOVA, LIAS and iNPH are different forms of chronic adulthood hydrocephalus and present different and peculiar clinical and radiological features, with an impact on the treatment and outcome prediction. The implementation of a clinical-radiological score for differential diagnosis may help the differentiation. Further studies are warranted.

Supplementary Information

The online version contains supplementary material available at 10.1007/s00701-022-05215-9.

Shunt Surgery Efficacy Is Correlated With Baseline Cerebrum Perfusion in Idiopathic Normal Pressure Hydrocephalus: A 3D Pulsed Arterial-Spin Labeling Study

This study investigated the relationship between preoperative cerebral blood flow (CBF) in patients with idiopathic normal pressure hydrocephalus (INPH) and preoperative clinical symptoms and changes of clinical symptoms after shunt surgery. A total of 32 patients with diagnosed INPH and 18 age-matched healthy controls (HCs) were involved in this study. All subjects underwent magnetic resonance imaging (MRI), including 3D pulsed arterial-spin labeling (PASL) for non-invasive perfusion imaging, and clinical symptom evaluation at baseline, and all patients with INPH were reexamined with clinical tests 1 month postoperatively. Patients with INPH had significantly lower whole-brain CBF than HCs, with the most significant differences in the high convexity, temporal lobe, precuneus, and thalamus. At baseline, there was a significant correlation between the CBF in the middle frontal gyrus, calcarine, inferior and middle temporal gyrus, thalamus, and posterior cingulate gyrus and poor gait manifestation. After shunting, improvements were negatively correlated with preoperative perfusion in the inferior parietal gyrus, inferior occipital gyrus, and middle temporal gyrus. Preoperative CBF in the middle frontal gyrus was positively correlated with the severity of preoperative cognitive impairment and negatively correlated with the change of postoperative MMSE score. There was a moderate positive correlation between anterior cingulate hypoperfusion and improved postoperative urination. Our study revealed that widely distributed and intercorrelated cortical and subcortical pathways are involved in the development of INPH symptoms, and preoperative CBF may be correlative to short-term shunt outcomes.

Aquaporin-4 and Cognitive Disorders

Aquaporin-4 (AQP4) is the most abundantly expressed aquaporin in the central nervous system (CNS) and is an integral part of the glymphatic system that cannot be ignored. The CNS has the glymphatic system instead of the conventional lymphatic system. The glymphatic system plays an essential role in the pathophysiological processes of many cognitive disorders. AQP4 shows noteworthy changes in various cognitive disorders and is part of the pathogenesis of these diseases. For this reason, AQP4 has attracted attention as a potential and promising target for regulating and even reversing cognitive dysfunction. This review will summarize the role of AQP4 in the pathophysiological processes of several cognitive disorders as reported in recent studies.

Normal-pressure hydrocephalus: A rare cause of reversible dementia

ABSTRACT

Normal-pressure hydrocephalus (NPH) is characterized by the clinical triad of dementia, gait instability, and urinary incontinence. The estimated annual incidence is 1.8 cases in 100,000 persons, making NPH a rare diagnosis and uncommon cause of dementia. NPH is a form of communicating hydrocephalus that can easily be missed in older adults with multiple comorbidities, so clinicians must exclude reversible causes of dementia before diagnosing irreversible causes such as Alzheimer disease.

Evaluation of aquaporins in the cerebrospinal fluid in patients with idiopathic normal pressure hydrocephalus

Brain aquaporin 1 (AQP1) and AQP4 are involved in cerebrospinal fluid (CSF) homeostasis and might participate in the origin of hydrocephalus. Studies have shown alterations of perivascular AQP4 expression in idiopathic normal pressure hydrocephalus (iNPH) and Alzheimer's disease (AD). Due to the overlapping of clinical signs between iNPH and certain neurological conditions, mainly AD, specific biomarkers might improve the diagnostic accuracy for iNPH. The goal of the present study was to analyze and quantify the presence of AQP1 and AQP4 in the CSF of patients with iNPH and AD to determine whether these proteins can be used as biomarkers of iNPH. We examined AQP1 and AQP4 protein levels in the CSF of 179 participants (88 women) classified into 5 groups: possible iNPH (81 participants), hydrocephalus associated with other neurological disorders (13 participants), AD (41 participants), non-AD dementia (32 participants) and healthy controls (12 participants). We recorded each participant's demographic and clinical variables and indicated, when available in the clinical history, the record of cardiovascular and respiratory complications. An ELISA showed virtually no AQP content in the CSF. Information on the vascular risk factors (available for 61 patients) confirmed some type of vascular risk factor in 86% of the patients with possible iNPH and 58% of the patients with AD. In conclusion, the ELISA analysis showed insufficient sensitivity to detect the presence of AQP1 and AQP4 in CSF, ruling out the possible use of these proteins as biomarkers for diagnosing iNPH.

Abdominal Pseudocyst: A Rare Complication of Ventriculoperitoneal Shunts

We present the case of a 69-year-old man patient who was brought with a history of gait disturbances, memory impairment, and urinary incontinence with gradual worsening over the past six months. The patient underwent magnetic resonance imaging of the brain which demonstrated enlarged ventricles, widening of the Sylvian fissure, and narrow sulci at the vertex. Subsequently, the patient underwent a lumbar puncture which revealed a normal opening pressure with normal cerebrospinal fluid analysis. The diagnosis of normal pressure hydrocephalus was established. The patient underwent a ventriculoperitoneal shunt for the management of his symptoms. Three years after the placement of the shunt, the patient was brought to the emergency department with an expanding right-sided subcutaneous abdominal mass. A computed tomography scan of the abdomen showed the subcutaneous mass superficial to the right rectus muscle and was containing the coiled distal end of the shunt. Such findings were consistent with a subcutaneous cerebrospinal fluid pseudocyst. The mass was aspirated and the fluid analysis was in keeping with the cerebrospinal fluid characteristics. The fluid culture revealed no bacterial growth. The ventriculoperitoneal shunt was replaced with a minimally invasive technique.

White Matter Microstructural Damage Associated With Gait Abnormalities in Idiopathic Normal Pressure Hydrocephalus

Background: Idiopathic normal pressure hydrocephalus (iNPH) is a common disease in elderly adults. Patients with iNPH are generally characterized by progressive gait impairment, cognitive deficits, and urinary urgency and/or incontinence. A number of radiographic studies have shown that iNPH patients have enlarged ventricles and altered brain morphology; however, few studies have focused on the relationships between altered brain structure and gait dysfunction due to iNPH. Thus, this study aimed to evaluate the abnormalities of white matter (WM) correlated with gait impairment in iNPH patients and to gain a better understanding of its underlying pathology. Methods: Fifteen iNPH patients (five women, 10 men) were enrolled in this study, and each patient's demographic and gait indices were collected. First, we performed a correlation analysis between the demographic and gait indices. Then, all gait indices were grouped according to the number of WM hyperintensities (WMH) among each WM tract (JHU WM tractography atlas), to perform comparative analysis. Results: Considering sex and illness duration as covariates, correlation analysis showed a significantly negative correlation between step length (r = -0.80, p = 0.001), pace (r = -0.84, p = 2.96e-4), and age. After removing the effects of age, sex, and illness duration, correlation analysis showed negative correlation between step length (r = -0.73, p = 0.007), pace (r = -0.74, p = 0.005), and clinical-grade score and positive correlation between 3-m round trip time (r = 0.66, p = 0.021), rising time (r = 0.76, p = 0.004), and clinical-grade score. Based on WMH of each white matter tract, gait indices showed significant differences (p < 0.05/48, corrected by Bonferroni) between fewer WMH patients and more WMH in the middle cerebellar peduncle, left medial lemniscus, left posterior limb of the internal capsule (IC), and right posterior limb of the IC. Conclusions: Our results indicated that iNPH patients exhibited gait-related WM abnormalities located in motor and sensory pathways around the ventricle, which is beneficial to understand the underlying pathology of iNPH.

Acute low-pressure hydrocephalus: a case series and systematic review of 195 patients

OBJECTIVE

Acute low-pressure hydrocephalus (ALPH) is characterized by clinical manifestations of an apparent raised intracranial pressure (ICP) and ventriculomegaly despite measured ICP that is below the expected range (i.e., typically ≤ 5 cm H2O). ALPH is often refractory to standard hydrocephalus intervention protocols and the ICP paradox commonly leads to delayed diagnosis. The aim of this study was to characterize ALPH and develop an algorithm to facilitate diagnosis and management for patients with ALPH.

METHODS

EMBASE, MEDLINE, and Google Scholar databases were searched for ALPH cases from its first description in 1994 until 2019. Cases that met inclusion criteria were pooled with cases managed at the authors' institution. Patient characteristics, presenting signs/symptoms, precipitating factors, temporizing interventions, definitive treatment, and patient outcomes were recorded.

RESULTS

There were 195 patients identified, with 42 local and 153 from the literature review (53 pediatric patients and 142 adults). Decreased level of consciousness was the predominant clinical sign. The most common etiologies of hydrocephalus were neoplasm and hemorrhage. While the majority of ALPH occurred spontaneously, 39% of pediatric patients had previously undergone a lumbar puncture. Prior to ALPH diagnosis, 92% of pediatric and 39% of adult patients had a ventricular shunt in situ. The most common temporizing intervention was subatmospheric CSF drainage. The majority of patients underwent a shunt insertion/revision or endoscopic third ventriculostomy as definitive ALPH treatment. Although the mortality rate was 11%, 83% of pediatric and 49% of adult patients returned to their pre-ALPH neurological functional status after definitive treatment. Outcomes were related to both the severity of the underlying neurosurgical disease causing the hydrocephalus and the efficacy of ALPH treatment.

CONCLUSIONS

ALPH is an underrecognized variant phenotype of hydrocephalus that is associated with multiple etiologies and can be challenging to treat as it frequently does not initially respond to standard strategies of CSF shunting. With early recognition, ALPH can be effectively managed. A management algorithm is provided as a guide for this purpose.

The CERAD Neuropsychological Battery in Patients with Idiopathic Normal Pressure Hydrocephalus Compared with Normal Population and Patients with Mild Alzheimer's Disease

BACKGROUND

The usefulness of CERAD Neuropsychological Battery for describing the cognitive impairment in idiopathic normal pressure hydrocephalus (iNPH) is unknown.

OBJECTIVE

To compare the cognitive profile of patients with iNPH to patients with mild Alzheimer's disease (AD) and age-matched cognitively healthy individuals by using the CERAD-NB.

METHODS

We studied CERAD-NB subtest results, including the Mini-Mental State Examination (MMSE), between 199 patients with probable iNPH, 236 patients with mild AD, and 309 people with normal cognition, using age, education, and gender adjusted multivariate linear regression model. In addition, the effects of AD-related brain pathology detected in frontal cortical brain biopsies in iNPH patients' cognitive profiles were examined.

RESULTS

The iNPH patients performed worse than cognitively healthy people in all CERAD-NB subtests. Despite similar performances in the MMSE, AD patients outperformed iNPH patients in Verbal Fluency (p = 0.016) and Clock Drawing (p < 0.001) tests. However, iNPH patients outperformed AD patients in the Boston Naming Test and Word List Recall and Recognition (p < 0.001). AD-related pathology in brain biopsies did not correlate with the CERAD-NB results.

CONCLUSION

At the time of the iNPH diagnosis, cognitive performances differed from cognitively healthy people in all CERAD-NB subtests. When the iNPH and AD patients' results were compared, the iNPH patients performed worse in Verbal Fluency and Clock Drawing tests while the AD group had more pronounced episodic memory dysfunctions. This study demonstrates significant differences in the CERAD-NB subtests between cognitive profiles of iNPH and AD patients. These differences are not captured by the MMSE alone.

Elevated CSF LRG and Decreased Alzheimer's Disease Biomarkers in Idiopathic Normal Pressure Hydrocephalus

Leucine-rich-alpha-2-glykoprotein (LRG) is suggested as a potential biomarker for idiopathic normal pressure hydrocephalus (iNPH). Our goal was to compare the cerebrospinal fluid (CSF) LRG levels between 119 iNPH patients and 33 age-matched controls and with the shunt responses and the brain biopsy Alzheimer’s disease (AD) pathology among the iNPH patients. CSF LRG, Aβ_1-42, P-tau₁₈₁, and T-tau were measured by using commercial ELISAs. The LRG levels in the CSF were significantly increased in the iNPH patients (p < 0.001) as compared to the controls, regardless of the AD pathology. However, CSF LRG did not correlate with the shunt response in contrast to the previous findings. The CSF AD biomarkers, i.e., Aβ_1-42, T-tau, and P-tau correlated with the brain biopsy AD pathology as expected but were systematically lower in the iNPH patients when compared to the controls (<0.001). Our findings support that the LRG levels in the CSF are potentially useful for the diagnostics of iNPH, independent of the brain AD pathology, but contrary to previous findings, not for predicting the shunt response. Our findings also suggest a need for specific reference values of the CSF AD biomarkers for the diagnostics of comorbid AD pathology in the iNPH patients.

A venous mechanism of ventriculomegaly shared between traumatic brain injury and normal ageing

Recently, age-related timing dissociation between the superficial and deep venous systems has been observed; this was particularly pronounced in patients with normal pressure hydrocephalus, suggesting a common mechanism of ventriculomegaly. Establishing the relationship between venous drainage and ventricular enlargement would be clinically relevant and could provide insight into the mechanisms underlying brain ageing. To investigate a possible link between venous drainage and ventriculomegaly in both normal ageing and pathological conditions, we compared 225 healthy subjects (137 males and 88 females) and 71 traumatic brain injury patients of varying ages (53 males and 18 females) using MRI-based volumetry and a novel perfusion-timing analysis. Volumetry, focusing on the CSF space, revealed that the sulcal space and ventricular size presented different lifespan profiles with age; the latter presented a quadratic, rather than linear, pattern of increase. The venous timing shift slightly preceded this change, supporting a role for venous drainage in ventriculomegaly. In traumatic brain injury, a small but significant disease effect, similar to idiopathic normal pressure hydrocephalus, was found in venous timing, but it tended to decrease with age at injury, suggesting an overlapping mechanism with normal ageing. Structural bias due to, or a direct causative role of ventriculomegaly was unlikely to play a dominant role, because of the low correlation between venous timing and ventricular size after adjustment for age in both patients and controls. Since post-traumatic hydrocephalus can be asymptomatic and occasionally overlooked, the observation suggested a link between venous drainage and CSF accumulation. Thus, hydrocephalus, involving venous insufficiency, may be a part of normal ageing, can be detected non-invasively, and is potentially treatable. Further investigation into the clinical application of this new marker of venous function is therefore warranted.

The Pathogenesis Based on the Glymphatic System, Diagnosis, and Treatment of Idiopathic Normal Pressure Hydrocephalus

Idiopathic normal pressure hydrocephalus (iNPH) is a rare neurological disorder with no clear prevalence factors and is a significant danger to the elderly. The intracranial glymphatic system is the internal environment that maintains brain survival and metabolism, and thus fluid exchange changes in the glymphatic system under various pathological conditions can provide important insights into the pathogenesis and differential diagnosis of many neurodegenerative diseases such as iNPH. iNPH can be diagnosed using a combination of clinical symptoms, imaging findings and history, and cerebrospinal fluid biomarkers due to the glymphatic system disorder. However, only few researchers have linked the two. Shunt surgery can improve the glymphatic system disorders in iNPH patients, and the surgical approach is determined using a combination of clinical diagnosis and trials. Therefore, we have composed this review to provide a future opportunity for elucidating the pathogenesis of iNPH based on the glymphatic system, and link the glymphatic system to the diagnosis and treatment of iNPH. The review will provide new insights into the medical research of iNPH.

Pathogenesis and pathophysiology of idiopathic normal pressure hydrocephalus

Idiopathic normal pressure hydrocephalus (iNPH), the most common type of adult-onset hydrocephalus, is a potentially reversible neuropsychiatric entity characterized by dilated ventricles, cognitive deficit, gait apraxia, and urinary incontinence. Despite its relatively typical imaging features and clinical symptoms, the pathogenesis and pathophysiology of iNPH remain unclear. In this review, we summarize current pathogenetic conceptions of iNPH and its pathophysiological features that lead to neurological deficits. The common consensus is that ventriculomegaly resulting from cerebrospinal fluid (CSF) dynamics could initiate a vicious cycle of neurological damages in iNPH. Pathophysiological factors including hypoperfusion, glymphatic impairment, disturbance of metabolism, astrogliosis, neuroinflammation, and blood-brain barrier disruption jointly cause white matter and gray matter lesions, and eventually lead to various iNPH symptoms. Also, we review the current treatment options and discuss the prospective treatment strategies for iNPH. CSF diversion with ventriculoperitoneal or lumboperitonealshunts remains as the standard therapy, while its complications prompt attempts to refine shunt insertion and develop new therapeutic procedures. Recent progress on advanced biomaterials and improved understanding of pathogenesis offers new avenues to treat iNPH.

Soluble Membrane Attack Complex: Biochemistry and Immunobiology

The soluble membrane attack complex (sMAC, a.k.a., sC5b-9 or TCC) is generated on activation of complement and contains the complement proteins C5b, C6, C7, C8, C9 together with the regulatory proteins clusterin and/or vitronectin. sMAC is a member of the MACPF/cholesterol-dependent-cytolysin superfamily of pore-forming molecules that insert into lipid bilayers and disrupt cellular integrity and function. sMAC is a unique complement activation macromolecule as it is comprised of several different subunits. To date no complement-mediated function has been identified for sMAC. sMAC is present in blood and other body fluids under homeostatic conditions and there is abundant evidence documenting changes in sMAC levels during infection, autoimmune disease and trauma. Despite decades of scientific interest in sMAC, the mechanisms regulating its formation in healthy individuals and its biological functions in both health and disease remain poorly understood. Here, we review the structural differences between sMAC and its membrane counterpart, MAC, and examine sMAC immunobiology with respect to its presence in body fluids in health and disease. Finally, we discuss the diagnostic potential of sMAC for diagnostic and prognostic applications and potential utility as a companion diagnostic.

Striatal Dopamine Deficit and Motor Impairment in Idiopathic Normal Pressure Hydrocephalus

BACKGROUND

Idiopathic normal pressure hydrocephalus can present with parkinsonism. However, abnormalities of the striatal dopamine reuptake transporter are unclear.

OBJECTIVES

To explore presence and features of striatal dopaminergic deficit in subjects with idiopathic normal pressure hydrocephalus as compared to Parkinson's disease (PD) patients and healthy controls.

METHODS

We investigated 50 subjects with idiopathic normal pressure hydrocephalus, 25 with PD, and 40 healthy controls. All participants underwent [¹²³ I]-N-ω-fluoropropyl-2β-carbomethoxy-3β-(4-iodophenyl)nortropane and single-photon emission computed tomography to quantify the striatal dopamine reuptake transporter binding. All subjects with idiopathic normal pressure hydrocephalus underwent a levodopa (l-dopa) challenge test and magnetic resonance imaging to evaluate ventriculomegaly and white matter changes. Gait, cognition, balance, and continence were assessed with the Idiopathic Normal Pressure Hydrocephalus Rating Scale, and parkinsonism with the motor section of the Movement Disorder Society-Unified Parkinson's Disease Rating Scale. All patients completed a 2-year follow-up.

RESULTS

A total of 62% of patients with idiopathic normal pressure hydrocephalus featured a reduced striatal dopamine reuptake transporter binding, which correlated with the severity of parkinsonism but not with features of ventriculomegaly or white matter changes. Unlike PD, this dopaminergic deficit in idiopathic normal pressure hydrocephalus was more symmetric and prominent in the caudate nucleus.

CONCLUSIONS

Subjects with idiopathic normal pressure hydrocephalus can present a reduction of striatal dopamine reuptake transporter binding, which is consistent with the severity of parkinsonism and qualitatively differs from that found in PD patients. Longitudinal interventional studies are needed to prove a role for striatal dopamine reuptake transporter deficit in the pathophysiology of idiopathic normal pressure hydrocephalus. © 2020 International Parkinson and Movement Disorder Society.

Usefulness of Brain Positron Emission Tomography with Different Tracers in the Evaluation of Patients with Idiopathic Normal Pressure Hydrocephalous

Idiopathic normal pressure hydrocephalus (iNPH) is the only form of dementia that can be cured by surgery. Its diagnosis relies on clinical and radiological criteria. Identifying patients who can benefit from surgery is challenging, as other neurological diseases can be concomitant or mimic iNPH. We performed a systematic review on the role of positron emission tomography (PET) in iNPH. We retrieved 35 papers evaluating four main functional aspects with different PET radiotracers: (1) PET with amyloid tracers, revealing Alzheimer's disease (AD) pathology in 20-57% of suspected iNPH patients, could be useful in predictions of surgical outcome. (2) PET with radiolabeled water as perfusion tracer showed a global decreased cerebral blood flow (CBF) and regional reduction of CBF in basal ganglia in iNPH; preoperative perfusion parameters could predict surgical outcome. (3) PET with 2-Deoxy-2-[18F]fluoroglucose ([18F]FDG ) showed a global reduction of glucose metabolism without a specific cortical pattern and a hypometabolism in basal ganglia; [18F]FDG PET may identify a coexisting neurodegenerative disease, helping in patient selection for surgery; postsurgery increase in glucose metabolism was associated with clinical improvement. (4) Dopaminergic PET imaging showed a postsynaptic D2 receptor reduction and striatal upregulation of D2 receptor after treatment, associated with clinical improvement. Overall, PET imaging could be a useful tool in iNPH diagnoses and treatment response.

NODDI in clinical research

Diffusion MRI (dMRI) has proven to be a useful imaging approach for both clinical diagnosis and research investigating the microstructures of nervous tissues, and it has helped us to better understand the neurophysiological mechanisms of many diseases. Though diffusion tensor imaging (DTI) has long been the default tool to analyze dMRI data in clinical research, acquisition with stronger diffusion weightings beyond the DTI regimen is now possible with modern clinical scanners, potentially enabling even more detailed characterization of tissue microstructures. To take advantage of such data, neurite orientation dispersion and density imaging (NODDI) has been proposed as a way to relate the dMRI signal to tissue features via biophysically inspired modeling. The number of reports demonstrating the potential clinical utility of NODDI is rapidly increasing. At the same time, the pitfalls and limitations of NODDI, and general challenges in microstructure modeling, are becoming increasingly recognized by clinicians. dMRI microstructure modeling is a rapidly evolving field with great promise, where people from different scientific backgrounds, such as physics, medicine, biology, neuroscience, and statistics, are collaborating to build novel tools that contribute to improving human healthcare. Here, we review the applications of NODDI in clinical research and discuss future perspectives for investigations toward the implementation of dMRI microstructure imaging in clinical practice.

Emergence and Developmental Roles of the Cerebrospinal Fluid System

We summarize recent work illuminating how cerebrospinal fluid (CSF) regulates brain function. More than a protective fluid cushion and sink for waste, the CSF is an integral CNS component with dynamic and diverse roles emerging in parallel with the developing CNS. This review examines the current understanding about early CSF and its maturation and roles during CNS development and discusses open questions in the field. We focus on developmental changes in the ventricular system and CSF sources (including neural progenitors and choroid plexus). We also discuss concepts related to the development of fluid dynamics including flow, perivascular transport, drainage, and barriers.

Prevalence of possible idiopathic normal pressure hydrocephalus in older inpatients with schizophrenia: a replication study

BACKGROUND

We recently reported that older patients with schizophrenia (SZ) show possible idiopathic normal pressure hydrocephalus (iNPH) more frequently than the general population. In this study, we estimated the prevalence of iNPH in a larger number of older SZ patients and explored useful examination values for diagnosis in the SZ population.

METHODS

We enrolled older inpatients with SZ (n = 39, mean age = 68.6 ± 7.7 years) from several psychiatric hospitals in Ehime, Japan and acquired brain imaging data using computed tomography. We evaluated three iNPH symptoms (dementia, gait disturbance, and urinary incontinence). In addition, we combined these data with our previous data to elucidate the relationship between iNPH and characteristics of SZ symptoms.

RESULTS

In total, five (12.8%) patients were diagnosed with possible iNPH. Evans' index for patients with iNPH was significantly higher than for those without iNPH (p = 0.002). The number of disproportionately enlarged subarachnoid space hydrocephalus (DESH) findings was significantly higher in patients with iNPH than in those without iNPH (p <  0.001). Using combined data, Drug-Induced Extra-pyramidal Symptoms Scale (DIEPSS) subscales of gait and bradykinesia showed an increasing trend in the SZ with iNPH group.

CONCLUSIONS

We reconfirmed that older inpatients with SZ experienced possible iNPH more frequently than the general population. We should pay attention to the DIEPSS subscales of gait and bradykinesia and DESH findings in addition to the three main symptoms of iNPH and Evans' index so as to not miss SZ patients with iNPH.

Brain Ventricular System and Cerebrospinal Fluid Development and Function: Light at the End of the Tube: A Primer with Latest Insights

The brain ventricular system is a series of connected cavities, filled with cerebrospinal fluid (CSF), that forms within the vertebrate central nervous system (CNS). The hollow neural tube is a hallmark of the chordate CNS, and a closed neural tube is essential for normal development. Development and function of the ventricular system is examined, emphasizing three interdigitating components that form a functional system: ventricle walls, CSF fluid properties, and activity of CSF constituent factors. The cellular lining of the ventricle both can produce and is responsive to CSF. Fluid properties and conserved CSF components contribute to normal CNS development. Anomalies of the CSF/ventricular system serve as diagnostics and may cause CNS disorders, further highlighting their importance. This review focuses on the evolution and development of the brain ventricular system, associated function, and connected pathologies. It is geared as an introduction for scholars with little background in the field.

Our Efforts in Understanding Normal Pressure Hydrocephalus: Learning from the 100 Most Cited Articles by Bibliometric Analysis

BACKGROUND

Normal pressure hydrocephalus (NPH) is a syndrome that was characterized several decades ago; however, its optimal diagnosis and management remain unclear. Our objective was to evaluate citation and bibliometric characteristics of the 100 most cited articles about NPH to better understand the state of research efforts in the field and where improvements may arise.

METHODS

Elsevier's Scopus database was searched for the 100 most cited articles that focused on NPH. Articles were characterized and various bibliometric parameters were compared. Categorical data were analyzed using Pearson χ², and continuous data were analyzed using either linear regression or a Student t test.

RESULTS

The 100 most cited articles were published between 1965 and 2014, from 16 unique countries in 38 unique journals. The most common outcome types of these articles were clinical (n = 77). Median number of citations and rate of citations were 114 citations and 5.9 citations/year since publication, respectively, with a significant inverse linear relationship between the 2 parameters (P < 0.01). The most common year of publication was 2002 (n = 10), and the most common country of origin was the United States (n = 40). Higher citation rates were associated with more recent articles (P < 0.01) and more authors (P < 0.01).

CONCLUSIONS

In the 100 most cited articles about NPH, there has been a distinct shift toward a more globalized effort in recent decades. The lack of more impactful articles in recent decades highlights that particular classic studies still penetrate practice and the possible need to reconsider our contemporary views on NPH to further advance the field.

Under pressure: Cerebrospinal fluid contribution to the physiological homeostasis of the eye

The cerebrospinal fluid (CSF) is a waterly, colorless fluid contained within the brain ventricles and the cranial and spinal subarachnoid spaces. CSF physiological functions range from hydromechanical protection of the central nervous system (CNS) to CNS modulation of developmental processes and regulation of interstitial fluid homeostasis. Optic nerve (ON) is surrounded by CSF circulating in the subarachnoid spaces and is exposed to both CSF (CSFP) and intra ocular (IOP) pressures, which converge at the lamina cribrosa (LC) as two opposite forces. The trans-lamina cribrosa pressure gradient (TLPG) is defined as IOP - CSFP and its alterations (due either to an elevation in IOP or a reduction in ICP) could result in structural damaging of the ON, including glaucomatous changes. The purpose of this review is to update the readers on the CSF contribution in controlling the functions/dysfunctions of ON by regulating homeostasis at LC. We also highlight emerging parallelisms regarding the expression of cilia-related genes in the regulation of common functions of body fluids in both brain and eye structures.