CSF hypersecretion versus impaired CSF absorption in posthemorrhagic hydrocephalus: a systematic review

BACKGROUND

The molecular mechanisms underlying development of posthemorrhagic hydrocephalus (PHH) remain elusive. The aim of this systematic review was to evaluate existing literature on increased CSF secretion and impaired CSF absorption as pathogenic contributors to CSF accumulation in neonatal and adult PHH.

METHODS

The systematic review was conducted in accordance with the PRISMA guidelines. Relevant studies published before March 11th, 2023, were identified from PubMed and reference lists. Studies were screened for eligibility using predefined inclusion and exclusion criteria. Data from eligible studies were extracted and potential sources of bias were evaluated.

RESULTS

Nineteen studies quantified CSF production rates and/or CSF absorption capacity in human patients with PHH or animals with experimentally induced PHH. Increased CSF production was reported as early as 24 h and as late as 28 days post ictus in six out of eight studies quantifying CSF production rates in animals with experimentally induced PHH. Impaired CSF absorption was reported in all four studies quantifying CSF absorption capacity in human patients with PHH and in seven out of nine studies quantifying CSF absorption capacity in animals with experimentally induced PHH. Impaired CSF absorption was reported as early as 30 min and as late as 10 months post ictus.

CONCLUSIONS

The pathological CSF accumulation in PHH likely arises from a combination of increased CSF secretion and impaired CSF absorption, which may manifest at different time scales following a hemorrhagic event. Emergent evidence on increased CSF secretion by the choroid plexus may herald a paradigm shift in our understanding of PHH.

Normal Pressure Hydrocephalus Following Cranial Radiation: Identification of Shunting Responders

BACKGROUND

We examined cognitive, brain MRI, and lumbar infusion test (LIT) features to identify predictors of response to ventriculoperitoneal shunting (VPS) in long-term cancer survivors with suspected normal pressure hydrocephalus (NPH) following cranial radiotherapy (RT).

METHODS

Patients who completed cranial RT at least 2 years before with clinically suspected NPH and an Evans' index (EI) ≥ 0.30 underwent a cognitive and a cerebrospinal fluid (CSF) volumetric (MRI) analysis (n = 36). For those in whom VPS was placed (n = 14), we explored whether adding a CSF volumetric analysis to classical MRI and LIT (Tap Test) features would better identify VPS responders.

RESULTS

Nearly 80% exhibited cognitive impairment. The CSF volume at NPH diagnoses was significantly larger in the group of VPS responders (p = 0.04). The addition of CSF volume to NPH diagnoses increased accuracy to 93%, with a positive and negative predictive value of 91% and 100%, respectively.

CONCLUSION

The addition of a quantitative MRI analysis of CSF volume to classical MRI and LIT NPH criteria, along with a high clinical suspicion of NPH, may help to identify VPS responders, thus improving the clinical management and prognosis of long-term survivors.

Prediction of Shunt Responsiveness in Suspected Patients With Normal Pressure Hydrocephalus Using the Lumbar Infusion Test: A Machine Learning Approach

BACKGROUND

Machine learning (ML) approaches can significantly improve the classical Rout-based evaluation of the lumbar infusion test (LIT) and the clinical management of the normal pressure hydrocephalus.

OBJECTIVE

To develop a ML model that accurately identifies patients as candidates for permanent cerebral spinal fluid shunt implantation using only intracranial pressure and electrocardiogram signals recorded throughout LIT.

METHODS

This was a single-center cohort study of prospectively collected data of 96 patients who underwent LIT and 5-day external lumbar cerebral spinal fluid drainage (external lumbar drainage) as a reference diagnostic method. A set of selected 48 intracranial pressure/electrocardiogram complex signal waveform features describing nonlinear behavior, wavelet transform spectral signatures, or recurrent map patterns were calculated for each patient. After applying a leave-one-out cross-validation training-testing split of the data set, we trained and evaluated the performance of various state-of-the-art ML algorithms.

RESULTS

The highest performing ML algorithm was the eXtreme Gradient Boosting. This model showed a good calibration and discrimination on the testing data, with an area under the receiver operating characteristic curve of 0.891 (accuracy: 82.3%, sensitivity: 86.1%, and specificity: 73.9%) obtained for 8 selected features. Our ML model clearly outperforms the classical Rout-based manual classification commonly used in clinical practice with an accuracy of 62.5%.

CONCLUSION

This study successfully used the ML approach to predict the outcome of a 5-day external lumbar drainage and hence which patients are likely to benefit from permanent shunt implantation. Our automated ML model thus enhances the diagnostic utility of LIT in management.

Communicating chronic hydrocephalus: A review

Formerly called normal pressure hydrocephalus, communicating chronic hydrocephalus (CCH) is a condition affecting 0.1 to 0.5% of patients over 60years of age. The pathophysiology of this disease is poorly understood, but a defect in cerebrospinal fluid (CSF) resorption appears to be commonly defined as the cause of the neurological disorders. The last important discovery is the description of the glymphatic system and its implication in CCH and CSF resorption. Comorbidities (Alzheimer's disease, microangiopathy, parkinsonism) are very frequent, and involve a diagnostic challenge. The clinical presentation is based on the Hakim and Adams triad, comprising gait disorders, mainly impairing walking, cognitive disorders, affecting executive functions, episodic memory, visuospatial cognition, and sphincter disorders as urinary incontinence (detrusor hyperactivity). The diagnosis is suspected through a set of arguments, combining the clinical presentation, the radiological data of the magnetic resonance imaging (MRI) showing a ventriculomegaly associated with signs of transependymomous resorption of the CSF and disappearance of the cortical sulci, and the clinical response to the depletion of CSF. In the presence of all these elements, or a strong clinical suspicion, the standard treatment will be of a permanent CSF shunt, using a ventriculoatrial or ventriculoperitoneal shunt. The effectiveness of this treatment defines the diagnosis. The clinical improvement is better when treatment occurs early after the onset of the disorders, reaching 75 to 90% of motor improvement.

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.

Shunt infusion studies: impact on patient outcome, including health economics

Objectives

The diagnosis of shunt malfunction is often not straightforward. We have explored, in symptomatic shunted patients with hydrocephalus or pseudotumour cerebri syndrome (PTCS), the accuracy of CSF infusion tests in differentiating a functioning shunt from one with possible problems, and the health economic consequences.

Methods

Participants: hydrocephalus/PTCS patients with infusion tests performed from January 2013 until December 2015. We followed patients up after 6 and 12 months from the test to determine whether they had improved, had persisting symptoms or had required urgent revision. We calculated the total cost savings of revision versus infusion tests and standard protocol of revision and ICP monitoring versus infusion tests.

Results

Three hundred sixty-five shunt infusion tests had been performed where a shunt prechamber/reservoir was present. For hydrocephalus patients, more than half of the tests (~ 55%, 155 out of 280) showed no shunt malfunction versus 125 with possible malfunction (ages 4 months to 90 years old). For PTCS patients aged 10 to 77 years old, 47 had possible problems and 38 no indication for shunt malfunction. Overall, > 290 unnecessary revisions were avoided over 3 years’ time. Two hundred fifty-eight (> 85%) of those non-surgically managed, remained well, did not deteriorate and did not require surgery. No infections were associated with infusion studies. For Cambridge, the overall savings from avoiding revisions was £945,415 annually.

Conclusions

Our results provide evidence of the importance of shunt testing in vivo to confirm shunt malfunction. Avoiding unnecessary shunt revisions carries a strong health benefit for patients that also translates to a significant financial benefit for the National Health Service and potentially for other healthcare systems worldwide.

Electronic supplementary material

The online version of this article (10.1007/s00701-020-04212-0) contains supplementary material, which is available to authorized users.

Timing of intraventricular infusion test for diagnosing idiopathic normal pressure hydrocephalus

BACKGROUND

Infusion tests, which measure resistance to outflow (R_out), are used in selecting patients suspected for idiopathic normal pressure hydrocephalus (iNPH) for shunt surgery. Infusion tests can be performed through an external ventricular drain (EVD). A 24-hour time gap from EVD insertion to an infusion test is a routine practice at our department due to concerns that the surgical procedure might influence the test results in the immediate postoperative period. The objective of the study was to investigate if timing of an intraventricular infusion test influences the results of the test in patients suspected for iNPH.

METHODS

Ten patients scheduled for an intraventricular infusion test were included. Measurements of baseline intracranial pressure (ICP) and plateau ICP were obtained during constant rate intraventricular infusion test performed at two time points (1 and 24 h after EVD insertion) and R_out was calculated from these measures and compared within patients.

RESULTS

Eight patients completed both infusion tests. In one of the 18 infusion tests performed, it was not possible to define an ICP plateau and this infusion test was excluded, leaving 7 paired infusion tests. Median R_out was 12.9 mmHg/ml/min (range 7.0-22.0) 1 h after EVD insertion and 11.3 mmHg/ml/min (range 7.8-18.1) after 24 h. Overall, there were no statistically significant differences in R_out (P = 0.83), baseline ICP (P = 0.70), or plateau ICP (P = 0.81) between the recordings performed 1 h and 24 h after EVD insertion. For two of the seven patients with paired infusion tests, there was poor agreement between R_out values at 1 and 24 h.

CONCLUSION

Overall, R_out estimates do not change significantly between 1 and 24 h after EVD insertion. We therefore propose that infusion tests can be performed shortly after surgery to reduce the period of indwelling EVD and duration of hospitalization.

Validation of Davson's equation in patients suffering from idiopathic normal pressure hydrocephalus

INTRODUCTION

The so-called Davson's equation relates baseline intracranial pressure (ICP) to resistance to cerebrospinal fluid outflow (Rout), formation of cerebrospinal fluid (I_f) and sagittal sinus pressure (P_SS) There is a controversy over whether this fundamental equation is applicable in patients with normal pressure hydrocephalus (NPH). We investigated the relationship between Rout and ICP and also other compensatory, clinical and demographic parameters in NPH patients.

METHOD

We carried out a retrospective study of 229 patients with primary NPH who had undergone constant-rate infusion studies in our hospital. Data was recorded and processed using ICM+ software. Relationships between variables were sought by calculating Pearson product correlation coefficients and p values.

RESULTS

We found a significant, albeit weak, relationship between ICP and Rout (R = 0.17, p = 0.0049), Rout and peak-to-peak amplitude of ICP (AMP) (R = 0.27, p = 3.577e-05) and Rout and age (R = 0.16, p = 0.01306).

CONCLUSIONS

The relationship found between ICP and Rout provides indirect evidence to support disturbed Cerebrospinal fluid circulation as a key factor in disturbed CSF dynamics in NPH. Weak correlation may indicate that other factors-variable P_SS and formation of CSF outflow-contribute heavily to linear model expressed by Davson's equation.

ICP Monitoring and Phase-Contrast MRI to Investigate Intracranial Compliance

OBJECTIVE

The amplitude of intracranial pressure (ICP) can be measured by ICP monitoring. Phase-contrast magnetic resonance imaging (PCMRI) can quantify blood and cerebrospinal fluid (CSF) flows. The aim of this work was to investigate intracranial compliance at rest by combining baseline ICP monitoring and PCMRI in hydrocephalus patients.

MATERIALS AND METHODS

ICP monitoring was performed before infusion testing to quantify ΔICP_rest at the basal condition in 33 suspected hydrocephalus patients (74 years). The day before, patients had had a PCMRI to assess total cerebral blood flow (tCBF), intracranial blood volume change (stroke volume SVblood), and cervical CSF volume change (the stroke volume CSV). Global (blood and CSF) intracranial volume change (ΔIVC) during each cardiac cycle (CC) was calculated. Finally, Compliance: C_rest = ΔIVC/ΔICP_rest was calculated. The data set was postprocessed by two operators according to blind analysis.

RESULTS

Bland-Altman plots showed that measurements presented no significant difference between the two operators. ΔICP_rest = 2.41 ± 1.21 mmHg, tCBF = 469.89 ± 127.54 mL/min, SVblood = 0.82 ± 0.32 mL/cc, CSV = 0.50 ± 0.22 mL/cc, ΔIVC = 0.44 ± 0.22 mL, and C_rest = 0.23 ± 0.15 mL/mmHg. There are significant relations between SVblood and CSV and also SVblood and tCBF.

CONCLUSIONS

During "basal" condition, the compliance amplitude of the intracranial compartment is heterogeneous in suspected hydrocephalus patients, and its value is lower than expected! This new parameter could represent new information, complementary to conventional infusion tests. We hope that this information can be applied to improve the selection of patients for shunt surgery.

Supplementary Tests in Idiopathic Normal Pressure Hydrocephalus: A Single-Center Experience with a Combined Lumbar Infusion Test and Tap Test

BACKGROUND

The lumbar infusion test (LIT) and tap test (TT) have previously been described for the diagnosis and selection of appropriate surgical candidates in idiopathic normal pressure hydrocephalus (iNPH).

METHODS

We retrospectively reviewed 81 consecutive patients with a clinical diagnosis of iNPH selected for supplementary testing. Clinical evaluation was scored with the Japanese Grading Scale for Normal Pressure Hydrocephalus, the Global Deterioration Score, and the modified Rankin Scale (mRS). The test protocol included a cerebrospinal fluid pressure monitoring (PMi), an LIT, and a TT. Patients were selected for surgery if outflow resistance was ≥14 mm Hg/mL/minute or if a clinical improvement was recorded after TT.

RESULTS

Sixty-eight patients were selected for ventriculoperitoneal shunting; 72.8% had a positive PMi or LIT, 74.1% had a positive TT, and 63.0% were positive to both tests. Complications were all transient. Clinical evaluation at 12 months after shunting showed a global improvement in 60 patients (88.2%). Overall, 75.0% of patients had no significant disability (mRS score, 1 and 2), 20.6% had an mRS score of 3 or 4, and 4.4% had severe disability after surgery. The positive predictive value of PMi/LIT, TT, or both combined was similar (89.8, 90.0, and 88.2%); however, 21.7% of patients who improved after surgery were selected with either a positive LIT or TT alone.

CONCLUSIONS

LIT and TT are complementary and they can easily be combined in sequence with a low complication rate and high probability of selecting patients with iNPH who may benefit from ventriculoperitoneal shunt surgery.

Diagnosis and Treatment of Idiopathic Normal Pressure Hydrocephalus

PURPOSE OF REVIEW

This article provides neurologists with a pragmatic approach to the diagnosis and treatment of idiopathic normal pressure hydrocephalus (iNPH), including an overview of: (1) key symptoms and examination and radiologic findings; (2) use of appropriate tests to determine the patient's likelihood of shunt responsiveness; (3) appropriate referral to tertiary centers with expertise in complex iNPH; and (4) the contribution of neurologists to the care of patients with iNPH following shunt surgery.

RECENT FINDINGS

The prevalence of iNPH is higher than previously estimated; however, only a fraction of persons with the disorder receive shunt surgery. iNPH should be considered as a diagnosis for patients with unexplained symmetric gait disturbance, a frontal-subcortical pattern of cognitive impairment, and urinary urge incontinence, whose MRI scans show enlarged ventricles and whose comorbidities are not sufficient to explain their symptoms. Physiologically based tests, such as the tap test (large-volume lumbar puncture) or temporary spinal catheter insertion for external lumbar drainage with gait testing before and after CSF removal, or CSF infusion testing for measurement of CSF outflow resistance, can reliably identify patients who are likely to respond to shunt surgery. Properly selected patients have an 80% to 90% chance of responding to shunt surgery, and all symptoms can improve following shunt surgery. Longitudinal care involves investigating the differential diagnosis of any symptoms that either fail to respond to shunt surgery or that worsen after initial improvement from shunt surgery.

SUMMARY

Neurologists play an important role in the identification of patients who should be evaluated for possible iNPH. With contemporary diagnostic tests and treatment with programmable shunts, the benefit-to-risk ratio of shunt surgery is highly favorable. For more complex patients, tertiary centers with expertise in complex iNPH are available throughout the world.

Repeated assessment of suspected normal pressure hydrocephalus in non-shunted cases. A prospective study based on the constant rate lumbar infusion test

BACKGROUND

Only a few reports have been published on the natural history of non-shunted patients suspected of having NPH. The aim of this study is to follow up a group of such cases.

METHODS

It was possible to follow up 27 patients who had not been qualified for shunting after the primary diagnosis. An assessment of Hakim's triad was performed, together with an analysis of radiological parameters and the results of lumbar infusion tests (LITs), both on admission and at the later date (on average, after 5.6 months). All parameters were analyzed with respect to periventricular lucency (PVL), atrophy, type of NPH, and the age of the patients.

RESULTS

There were no deteriorations and six patients improved. Those who were over 50 and who had no PVL or secondary NPH tended to improve more frequently. Significant improvement of dementia was noted (p = 0.042) in all cases, and in the group of patients without PVL (p = 0.04). The size of the ventricles did not change significantly. The values of the resistance to outflow (R), elastance (E), and ICP remained stable.

CONCLUSIONS

Analysis of our series revealed that the patients suspected of having NPH who had not been qualified for shunting did not deteriorate, while some of them even improved significantly as far as the level of dementia was concerned. As the CT and LIT parameters remained stable, there were no indications for repeating these examinations, at least within the period of nearly 6 months, which followed the primary diagnosis.

Spectral analysis of intracranial pressure: Is it helpful in the assessment of shunt functioning in-vivo?

OBJECTIVE

Shunt failure is common in hydrocephalic patients. The cerebrospinal fluid (CSF) infusion test enables the assessment of CSF absorption capacity, which is represented by the resistance to CSF outflow (ROUT) However, shunt failure may not only affect the CSF absorption capacity but also the intracranial compliance or compensatory properties. Spectral analysis of the ICP signal obtained during the infusion test may enable the comprehensive assessment of the overall deterioration caused by shunt failure.

MATERIAL AND METHODS

A total of 121 hydrocephalic shunted patients underwent the infusion test with continuous intracranial pressure (ICP) and arterial blood pressure (ABP) recording. The maximum amplitudes of three major frequency bandwidths (0.2-2.6, 2.6-4.0 and 4.0-15 Hz, respectively) were calculated from the ICP. Statistical analyses were conducted to identify factors significantly associated with shunt failure, to construct an index (i.e., the shunt response parameter, SRP) for detecting shunt failure, and to define thresholds for ROUT and SRP.

RESULTS

The ROUT threshold for detecting shunt failure was 7.59 mmHg/ml/min, and this threshold showed an accuracy of 82.64%. All spectral parameters were found to be significantly associated with shunt patency (p<0.05). The SRP exhibited significantly better accuracy than ROUT in detecting shunt failure (91.74%).

CONCLUSION

The hydrodynamic assessment of shunted patients enhanced by spectral analysis during the infusion test detected shunt failure with high accuracy. Although further validation is needed, the SRP exhibited promising results.

Idiopathic normal pressure hydrocephalus: diagnostic and predictive value of clinical testing, lumbar drainage, and CSF dynamics

OBJECTIVE The aim of the study was to analyze the diagnostic and predictive values of clinical tests, CSF dynamics, and intracranial pulsatility tests, compared with external lumbar drainage (ELD), for shunt response in patients with idiopathic normal pressure hydrocephalus (iNPH). METHODS Sixty-eight consecutive patients with suspected iNPH were prospectively evaluated. Preoperative assessment included clinical tests, overnight intracranial pressure (ICP) monitoring, lumbar infusion test (LIFT), and ELD for 24-72 hours. Simple and multiple linear regression analyses were conducted to identify predictive parameters concerning the outcome after shunt therapy. RESULTS Positive response to ELD correctly predicted improvement after CSF diversion in 87.9% of the patients. A Mini-Mental State Examination (MMSE) value below 21 was associated with nonresponse after shunt insertion (specificity 93%, sensitivity 67%). Resistance to outflow of CSF (ROut) > 12 mm Hg/ml/min was false negative in 21% of patients. Intracranial pulsatility parameters yielded different results in various parameters (correlation coefficient between pulse amplitude and ICP, slow wave amplitude, and mean ICP) but did not correlate to outcome. In multiple linear regression analysis, a calculation of presurgical MMSE versus the value after ELD, ROut, and ICP amplitude quotient during LIFT was significantly associated with outcome (p = 0.04). CONCLUSIONS Despite a multitude of invasive tests, presurgical clinical testing and response to ELD yielded the best prediction for improvement of symptoms following surgery. The complication rate of invasive testing was 5.4%. Multiple and simple linear regression analyses indicated that outcome can only be predicted by a combination of parameters, in accordance with a multifactorial pathogenesis of iNPH.