The Tight Medial and High Convexity Subarachnoid Spaces Is the First Finding of Idiopathic Normal Pressure Hydrocephalus at the Preclinical Stage

Brain positron emission tomography in idiopathic normal-pressure hydrocephalus: new 18 F-fluorodeoxyglucose pattern in a long-known syndrome

AIM

Patients with idiopathic normal-pressure hydrocephalus (iNPH) can show a global reduction in cerebral glucose metabolism at [ 18 F]Fluorodeoxyglucose (FDG) PET. The presence of caudate hypometabolism has been identified as a potential biomarker in iNPH, yet there is limited evidence of hypermetabolic findings in patients with iNPH so far.

METHODS

We retrieved retrospectively patients with iNPH and normal cognitive assessment, evaluated before surgery undergoing brain [ 18 F]FDG-PET. The 18 F-FDG-PET brain scans were compared to those of a control group of healthy subjects, matched for age and sex, by statistical parametric mapping (SPM) to identify areas of relative hypo- and hypermetabolism. Furthermore, the existence of a correlation between areas of hypo- and hypermetabolism in the patient group was tested.

RESULTS

Seven iNPH patients (mean age 74 ± 6 years) were found in the hospital database. SPM group analysis revealed clusters of significant hypometabolism ( P  = 0.001) in the iNPH group in the dorsal striatum, involving caudate and putamen bilaterally. Clusters of significant hypermetabolism ( P  = 0.001) were revealed in the bilateral superior and precentral frontal gyrus (BA 4, 6). A significant inverse correlation between striatal hypometabolism and bilateral superior and precentral frontal gyrus hypermetabolism was revealed ( P  < 0.001 corrected for multiple comparisons).

CONCLUSION

In this cohort, patients with iNPH showed subcortical hypometabolism, including bilateral dorsal striatum. To the best of our knowledge, this is the first report demonstrating a hypermetabolic pattern in the primary motor and premotor areas, and showing an inverse correlation between the striatum and motor cortex in patients with iNPH.

Tightened Sulci in the High Convexities as a Noteworthy Feature of Idiopathic Normal Pressure Hydrocephalus

OBJECTIVE

The presence of tightened sulci in the high-convexities (THC) is a key morphological feature for the diagnosis of idiopathic normal pressure hydrocephalus (iNPH), but the exact localization of THC has yet to be defined. The purpose of this study was to define THC and compare its volume, percentage, and index between iNPH patients and healthy controls.

METHODS

According to the THC definition, the high-convexity part of the subarachnoid space was segmented and measured the volume and percentage from the 3D T1-weighted and T2-weighted magnetic resonance images in 43 patients with iNPH and 138 healthy controls.

RESULTS

THC was defined as a decrease in the high-convexity part of the subarachnoid space located above the body of the lateral ventricles, with anterior end on the coronal plane perpendicular to the anterior commissure-posterior commissure (AC-PC) line passing through the front edge of the genu of corpus callosum, the posterior end in the bilateral posterior parts of the callosomarginal sulci, and the lateral end at 3 cm from the midline on the coronal plane perpendicular to the AC-PC line passing through the midpoint between AC and PC. Compared to the volume and volume percentage, the high-convexity part of the subarachnoid space volume per ventricular volume ratio < 0.6 was the most detectable index of THC on both 3D T1-weighted and T2-weighted magnetic resonance images.

CONCLUSIONS

To improve the diagnostic accuracy of iNPH, the definition of THC was clarified, and high-convexity part of the subarachnoid space volume per ventricular volume ratio <0.6 proposed as the best index for THC detection in this study.

Incidental findings of typical iNPH imaging signs in asymptomatic subjects with subclinical cognitive decline

Background

The etiology of idiopathic normal pressure hydrocephalus (iNPH) remains unclear. Little is known about the pre-symptomatic stage. This study aimed to investigate the association of neuropsychological data with iNPH-characteristic imaging changes compared to normal imaging and unspecific atrophy in a healthy population.

Methods

We extracted data from the community-dwelling Austrian Stroke Prevention Family Study (ASPS-Fam) database (2006–2010). All subjects underwent a baseline and identical follow-up examination after 3–5 years with MR imaging and an extensive neuropsychological test battery (Trail Making Test B, short physical performance balance, walking speed, memory, visuo-practical skills, composite scores of executive function and g-factor). We categorized the subjects into “iNPH”-associated, non-specific “atrophy,” and “normal” based on the rating of different radiological cerebrospinal fluid (CSF) space parameters. We noted how the categories developed over time. We assessed the association of the image categories with the neuropsychological data, different demographic, and lifestyle parameters (age, sex, education, alcohol intake, arterial hypertension, hypercholesterolemia), and the extent of white matter hyperintensities. We investigated whether neuropsychological data associated with the image categories were independent from other parameters as confounders.

Results

One hundred and thirteen subjects, aged 50–70 years, were examined. The imaging category “iNPH” was only present at follow-up. A third of subjects with “atrophy” at baseline changed to the category “iNPH” at follow-up. More white matter hyperintensities (WMH) were present in later “iNPH” subjects. Subjects with “iNPH” performed worse than “normal” subjects on executive function (p = 0.0118), memory (p = 0.0109), and Trail Making Test B (TMT-B. p < 0.0001). Education, alcohol intake, diabetes, arterial hypertension, and hypercholesterolemia had no effect. Age, number of females, and the extent of white matter hyperintensities were higher in “iNPH” than in “normal” subjects but did not significantly confound the neuropsychological results.

Conclusions

Apparent asymptomatic subjects with “iNPH” imaging characteristics presented with subclinical cognitive decline and showed worse executive function, memory, and TMT-B results than “normal” subjects. WMH seem to play a role in the etiology before ventriculomegaly. Clinical screening of individuals with incidental iNPH-characteristic imaging and conspicuous results sof these neurocognitive tests needs further validation.

Neurofluids-Deep inspiration, cilia and preloading of the astrocytic network

With the advent of real-time MRI, the motion and passage of cerebrospinal fluid can be visualized without gating and exclusion of low-frequency waves. This imaging modality gives insights into low-volume, rapidly oscillating cardiac-driven movement as well as sustained, high-volume, slowly oscillating inspiration-driven movement. Inspiration means a spontaneous or artificial increase in the intrathoracic dimensions independent of body position. Alterations in thoracic diameter enable the thoracic and spinal epidural venous compartments to be emptied and filled, producing an upward surge of cerebrospinal fluid inside the spine during inspiration; this surge counterbalances the downward pooling of venous blood toward the heart. Real-time MRI, as a macroscale in vivo observation method, could expand our knowledge of neurofluid dynamics, including how astrocytic fluid preloading is adjusted and how brain buoyancy and turgor are maintained in different postures and zero gravity. Along with these macroscale findings, new microscale insights into aquaporin-mediated fluid transfer, its sensing by cilia, and its tuning by nitric oxide will be reviewed. By incorporating clinical knowledge spanning several disciplines, certain disorders-congenital hydrocephalus with Chiari malformation, idiopathic intracranial hypertension, and adult idiopathic hydrocephalus-are interpreted and reviewed according to current concepts, from the basics of the interrelated systems to their pathology.

Prognostic Utility of Disproportionately Enlarged Subarachnoid Space Hydrocephalus in Idiopathic Normal Pressure Hydrocephalus Treated with Ventriculoperitoneal Shunt Surgery: A Systematic Review and Meta-analysis

BACKGROUND

Disproportionately enlarged subarachnoid space hydrocephalus is a specific radiologic marker for idiopathic normal pressure hydrocephalus. However, controversy exists regarding the prognostic utility of disproportionately enlarged subarachnoid space hydrocephalus.

PURPOSE

Our aim was to evaluate the prevalence of disproportionately enlarged subarachnoid space hydrocephalus in idiopathic normal pressure hydrocephalus and its predictive utility regarding prognosis in patients treated with ventriculoperitoneal shunt surgery.

DATA SOURCES

We used MEDLINE and EMBASE databases.

STUDY SELECTION

We searched for studies that reported the prevalence or the diagnostic performance of disproportionately enlarged subarachnoid space hydrocephalus in predicting treatment response.

DATA ANALYSIS

The pooled prevalence of disproportionately enlarged subarachnoid space hydrocephalus was obtained. Pooled sensitivity, specificity, and area under the curve of disproportionately enlarged subarachnoid space hydrocephalus to predict treatment response were obtained. Subgroup and sensitivity analyses were performed to explain heterogeneity among the studies.

DATA SYNTHESIS

Ten articles with 812 patients were included. The pooled prevalence of disproportionately enlarged subarachnoid space hydrocephalus in idiopathic normal pressure hydrocephalus was 44% (95% CI, 34%-54%). The pooled prevalence of disproportionately enlarged subarachnoid space hydrocephalus was higher in the studies using the second edition of the Japanese Guidelines for Management of Idiopathic Normal Pressure Hydrocephalus compared with the studies using the international guidelines without statistical significance (52% versus 43%, P = .38). The pooled sensitivity and specificity of disproportionately enlarged subarachnoid space hydrocephalus for prediction of treatment response were 59% (95% CI, 38%-77%) and 66% (95% CI, 57%-74%), respectively, with an area under the curve of 0.67 (95% CI, 0.63-0.71).

LIMITATIONS

The lack of an established method for assessing disproportionately enlarged subarachnoid space hydrocephalus using brain MR imaging served as an important cause of the heterogeneity.

CONCLUSIONS

Our meta-analysis demonstrated a relatively low prevalence of disproportionately enlarged subarachnoid space hydrocephalus in idiopathic normal pressure hydrocephalus and a poor diagnostic performance for treatment response.

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.

Role of DESH, callosal angle and cingulate sulcus sign in prediction of gait responsiveness after shunting in iNPH patients

Primary endpoint of this single-centre, prospective consecutive cohort study was to evaluate DESH score, CA, CSS and Evans index of suspected iNPH patients against the reference standard of lumbar infusion test (LIT) and external lumbar drainage (ELD) in prediction of gait response after VP shunt implantation in patients with idiopathic normal pressure hydrocephalus (iNPH). Patients were assigned to NPH and non-NPH groups based on LIT and ELD results. Age-matched controls were added for group comparison. 32 NPH, 46 non-NPH and 15 control subjects were enrolled in the study. There were significant differences in mean preoperative DESH scores of NPH, non-NPH and control groups (6.3 ± 2.3 ([±SD]) (range 2-10) vs 4.5 ± 2.4 (range 0-10) vs 1.0 ± 1.2 (range 0-4)). Differences in mean CA and Evans index were not significant between NPH and non-NPH groups. CSS showed 62.5% sensitivity, 60.87% specificity, 52.63% PPV and 70% NPV for differentiation of NPH and non-NPH groups. A CA of 68 degrees had 48.49% sensitivity, 76.09% specificity, 59.26% PPV 67.31% NPV and DESH score of 4 had 93.75% sensitivity, 41.30% specificity, 52.63% PPV and 90.48% NPV for differentiation between NPH and non-NPH groups. The groups of probable iNPH patients with gait impairment diagnosed by high DESH score or positive functional testing did not overlap and DESH score did not correlate with gait improvement after ELD. DESH score should not be used as a simple diagnostic or prognostic marker of iNPH and we could not confirm the benefit of measurement of callosal angle and cingulate sulcus sign.

Association between the Onset of Idiopathic Normal Pressure Hydrocephalus Symptoms and Reduced Default Mode Network Connectivity

OBJECTIVE

The aim was to examine the association between connectivity changes in the default mode network (DMN) and the progression of idiopathic normal pressure hydrocephalus (iNPH).

METHODS

We retrospectively recruited cases of preclinical and clinical iNPH from 2,196 patients who had received whole-body 18F-fluorodeoxyglucose-positron emission tomography/computed tomography (FDG-PET/CT) scanning. We included 31 cases with asymptomatic ventriculomegaly with features of iNPH on MRI (AVIM; reported as preclinical iNPH) and 12 with iNPH. We performed a voxel-based analysis of the brain FDG-PET images of the AVIM and iNPH groups as well as for each background-matched normal control (NC) group, using Statistical Parametric Mapping 12. Volume of interest (VOI)-based analysis was also performed. We set the VOI as the region from the precuneus to the posterior cingulate cortices (PCC), and compared the mean regional standardized uptake value ratio (SUVR) between the AVIM and iNPH group FDG-PET/CT images and each corresponding NC group.

RESULTS

The voxel-based analysis showed a greater decreased FDG uptake in the PCC in the iNPH group than in the AVIM group. The VOI-based analysis revealed no significant difference in the mean SUVR of the AVIM group and the corresponding NC group, but that of the iNPH group was significantly lower than that of its corresponding NC group.

CONCLUSIONS

DMN connectivity was reduced in the clinical iNPH group but not in the preclinical group. These data suggest that alterations in the functional connectivity of the DMN are related to the onset of iNPH symptoms.

Reliability and Interobserver Variability of Evans' Index and Disproportionately Enlarged Subarachnoid Space Hydrocephalus as Diagnostic Criteria for Idiopathic Normal Pressure Hydrocephalus

Background:

The image diagnosis of idiopathic normal-pressure hydrocephalus (iNPH) is based on the ventriculomegaly, whose criterion is an Evans' Index (EI) >0.3. Recently, disproportionately enlarged subarachnoid space hydrocephalus (DESH) has been proposed as a morphological characteristic to iNPH. Several studies cast doubt on the reliability of these criteria in the diagnosis of iNPH. Furthermore, interobserver differences of these criteria have not yet been investigated. The objective of this study was to assess the diagnostic reliability and interobserver variability of EI and DESH.

Materials and Methods:

The preoperative magnetic resonance (MR) images of 84 definite iNPH patients were retrospectively evaluated by a neuroradiologist (NR) and physical therapist (PT). They independently assessed the EI and DESH. The MR images were evaluated preoperatively by a neurosurgeon (NS). The results were showed in mean (standard deviation).

Results:

The mean age was 78.4 (6.3) years (male:female = 49:35). The mean EI was 0.33 (0.04), 0.32 (0.04), and 0.31 (0.03) for NS, NR, and PT, respectively (P < 0.0001). The rate of accurate diagnosis of iNPH with EI >0.3 was 74%, 66%, and 61% for NS, NR, and PT, respectively, and there was a moderate level of agreement. By contrast, there was a substantial lower level of accuracy in assessment with DESH for all three evaluators as 50%, 44%, and 27% for NS, NR, and PT, respectively, again with a moderate level of agreement. However, the rates of patients fulfilling both EI >0.3 and DESH were remarkably lower than either of the two parameters individually at a mere 37%, 30%, and 16% for NS, NR, and PT, respectively, with a low level of agreement between the rates.

Conclusion:

This study suggests that DESH cannot be a diagnostic criterion for iNPH. If EI >0.3 and DESH were both necessary to diagnose iNPH, then more than 70% of patients would have been misdiagnosed and would have been deprived of the chance of treatment and its benefits. These results request a paradigm shift in the concepts of iNPH.

Changes in cerebral glucose metabolism caused by morphologic features of prodromal idiopathic normal pressure hydrocephalus

Background

Decreased cerebral glucose metabolism has been reported in idiopathic normal pressure hydrocephalus (iNPH). However, the timing of appearance in the preclinical stage of iNPH remains unknown. Herein, we evaluated the changes in regional cerebral glucose metabolism with respect to the characteristic morphologic features of iNPH.

Methods

We performed a cross-sectional study in > 2000 elderly patients who received a whole body 18F-fluorodeoxyglucose-positron emission tomography/computed tomography scanning and recruited subjects with clinical and preclinical iNPH. We included 12 subjects with iNPH, 32 subjects with asymptomatic ventriculomegaly with features of iNPH on magnetic resonance imaging (AVIM), and 33 subjects with preclinical morphologic features of DESH (PMD). We previously reported that iNPH develops in the order of PMD (asymptomatic subjects with incomplete DESH), AVIM (asymptomatic subjects with DESH), and iNPH (symptomatic subjects with DESH). We measured the median regional standardized uptake value ratio (SUVR) on 18F-fluorodeoxyglucose-positron emission tomography/computed tomography images between the three groups and compared them with background-matched normal controls in the frontal lobes, temporal lobes, medial parietal lobes, striata, and thalami.

Results

In the frontal and temporal lobes, the SUVR distributions of the PMD, AVIM, and PMD groups were significantly lower than for each NC (p < 0.05 for all). In the medial parietal lobes, the SUVR distributions were significantly higher in PMD and AVIM groups (p < 0.05 for all). In the thalami and striata, the SUVR distributions were significantly lower in the iNPH group (p < 0.05 for all).

Conclusions

Changes in brain glucose metabolism in the cortices are observed in preclinical iNPH, while metabolic decline in the basal ganglia is only detected in clinical iNPH.