Evaluation of pediatric hydrocephalus by computed tomography

Bulat-Klarica-Oreskovic Hypothesis: A Comprehensive Review

Classical theories of cerebrospinal fluid (CSF) production and flow are taught throughout medical education. The idea that CSF is produced and/or filtered by the choroid plexus and flows in one direction throughout the ventricular system has been a largely accepted thesis. However, modern studies have called into question the validity of this hypothesis, suggesting that CSF does not move unidirectionally but rather is driven by microvessel contractions in a to-and-fro manner throughout the cerebrospinal system. Moreover, new insights suggest that in addition to CSF production, the exchange of fluids and proteins between the cortical vasculature and the interstitium may function as the brain's version of a lymphatic system. This comprehensive review provides evidence for a different framework of CSF flow. One that includes perivascular pulsations that push CSF back and forth, allowing exchange between the CSF and interstitium, and with CSF production occurring throughout the cerebrospinal system. These findings could be revolutionary in understanding the pathophysiology of CSF flow and in the treatment of pathologies such as intracranial hypertension, hydrocephalus, Alzheimer's disease, and many others.

Etiology- and region-specific characteristics of transependymal cerebrospinal fluid flow

OBJECTIVE

Transependymal flow (TEF) of CSF, often delineated as T2-weighted hyperintensity adjacent to the lateral ventricles on MRI, is a known imaging finding, usually in the setting of CSF flow disturbances. Specific radiological features of TEF and their relationships with clinical markers of hydrocephalus and underlying disease pathology are not known. Here, the authors describe the radiological features and clinical associations of TEF with implications for CSF circulation in the setting of intracranial pathology.

METHODS

After obtaining IRB review and approval, the authors reviewed the radiological records of all patients who underwent intracranial imaging with CT or MRI at St. Louis Children's Hospital, St. Louis, Missouri, between 2008 and 2019 to identify individuals with TEF. Then, under direct review of imaging, TEF pattern, degree, and location and underlying pathology and other radiological and clinical features pertaining to CSF circulation and CSF disturbances were noted.

RESULTS

TEF of CSF was identified in 219 patients and was most prevalent in the setting of neoplasms (72%). In 69% of the overall cohort, TEF was seen adjacent to the anterior aspect of the frontal horns and the posterior aspect of the occipital horns of the lateral ventricles, and nearly half of these patients also had TEF dorsal to the third ventricle near the splenium of the corpus callosum. This pattern was independently associated with posterior fossa medulloblastoma when compared with pilocytic astrocytoma (OR 4.75, 95% CI 1.43-18.53, p = 0.0157). Patients with congenital or neonatal-onset hydrocephalus accounted for 13% of patients and were more likely to have TEF circumferentially around the ventricles without the fronto-occipital distribution. Patients who ultimately required permanent CSF diversion surgery were more likely to have the circumferential TEF pattern, a smaller degree of TEF, and a lack of papilledema at the time of CSF diversion surgery.

CONCLUSIONS

CSF transmigration across the ependyma is usually restricted to specific periventricular regions and is etiology specific. Certain radiological TEF characteristics are associated with tumor pathology and may reflect impaired or preserved ependymal fluid handling and global CSF circulation. These findings have implications for TEF as a disease-specific marker and in understanding CSF handling within the brain.

Review of Cerebrospinal Fluid Physiology and Dynamics: A Call for Medical Education Reform

BACKGROUND

The flow of cerebrospinal fluid (CSF) has been described as a unidirectional system with the choroid plexus serving as the primary secretor of CSF and the arachnoid granulations as primary reabsorption site. This theory of neurosurgical forefathers has been universally adopted and taught as dogma. Many neuroscientists have found difficulty reconciling this theory with common pathologies, and recent studies have found that this "classic" hypothesis may not represent the full picture.

OBJECTIVE

To review modern CSF dynamic theories and to call for medical education reform.

METHODS

We reviewed the literature from January 1990 to December 2020. We searched the PubMed database using key terms "cerebrospinal fluid circulation," "cerebrospinal fluid dynamics," "cerebrospinal fluid physiology," "glymphatic system," and "glymphatic pathway." We selected articles with a primary aim to discuss either CSF dynamics and/or the glymphatic system.

RESULTS

The Bulat-Klarica-Orešković hypothesis purports that CSF is secreted and reabsorbed throughout the craniospinal axis. CSF demonstrates similar physiology to that of water elsewhere in the body. CSF "circulates" throughout the subarachnoid space in a pulsatile to-and-fro fashion. Osmolarity plays a critical role in CSF dynamics. Aquaporin-4 and the glymphatic system contribute to CSF volume and flow by establishing osmolarity gradients and facilitating CSF movement. Multiple studies demonstrate that the choroid plexus does not play any significant role in CSF circulation.

CONCLUSION

We have highlighted major studies to illustrate modern principles of CSF dynamics. Despite these, the medical education system has been slow to reform curricula and update learning resources.

Hydrocephalus: Ventricular Volume Quantification Using Three-Dimensional Brain CT Data and Semiautomatic Three-Dimensional Threshold-Based Segmentation Approach

OBJECTIVE

To evaluate the usefulness of the ventricular volume percentage quantified using three-dimensional (3D) brain computed tomography (CT) data for interpreting serial changes in hydrocephalus.

MATERIALS AND METHODS

Intracranial and ventricular volumes were quantified using the semiautomatic 3D threshold-based segmentation approach for 113 brain CT examinations (age at brain CT examination ≤ 18 years) in 38 patients with hydrocephalus. Changes in ventricular volume percentage were calculated using 75 serial brain CT pairs (time interval 173.6 ± 234.9 days) and compared with the conventional assessment of changes in hydrocephalus (increased, unchanged, or decreased). A cut-off value for the diagnosis of no change in hydrocephalus was calculated using receiver operating characteristic curve analysis. The reproducibility of the volumetric measurements was assessed using the intraclass correlation coefficient on a subset of 20 brain CT examinations.

RESULTS

Mean intracranial volume, ventricular volume, and ventricular volume percentage were 1284.6 ± 297.1 cm³, 249.0 ± 150.8 cm³, and 19.9 ± 12.8%, respectively. The volumetric measurements were highly reproducible (intraclass correlation coefficient = 1.0). Serial changes (0.8 ± 0.6%) in ventricular volume percentage in the unchanged group (n = 28) were significantly smaller than those in the increased and decreased groups (6.8 ± 4.3% and 5.6 ± 4.2%, respectively; p = 0.001 and p < 0.001, respectively; n = 11 and n = 36, respectively). The ventricular volume percentage was an excellent parameter for evaluating the degree of hydrocephalus (area under the receiver operating characteristic curve = 0.975; 95% confidence interval, 0.948-1.000; p < 0.001). With a cut-off value of 2.4%, the diagnosis of unchanged hydrocephalus could be made with 83.0% sensitivity and 100.0% specificity.

CONCLUSION

The ventricular volume percentage quantified using 3D brain CT data is useful for interpreting serial changes in hydrocephalus.

Exploring neurodegenerative disorders using a novel integrated model of cerebral transport: Initial results

The neurovascular unit (NVU) underlines the complex and symbiotic relationship between brain cells and the cerebral vasculature, and dictates the need to consider both neurodegenerative and cerebrovascular diseases under the same mechanistic umbrella. Importantly, unlike peripheral organs, the brain was thought not to contain a dedicated lymphatics system. The glymphatic system concept (a portmanteau of glia and lymphatic) has further emphasized the importance of cerebrospinal fluid transport and emphasized its role as a mechanism for waste removal from the central nervous system. In this work, we outline a novel multiporoelastic solver which is embedded within a high precision, subject specific workflow that allows for the co-existence of a multitude of interconnected compartments with varying properties (multiple-network poroelastic theory, or MPET), that allow for the physiologically accurate representation of perfused brain tissue. This novel numerical template is based on a six-compartment MPET system (6-MPET) and is implemented through an in-house finite element code. The latter utilises the specificity of a high throughput imaging pipeline (which has been extended to incorporate the regional variation of mechanical properties) and blood flow variability model developed as part of the VPH-DARE@IT research platform. To exemplify the capability of this large-scale consolidated pipeline, a cognitively healthy subject is used to acquire novel, biomechanistically inspired biomarkers relating to primary and derivative variables of the 6-MPET system. These biomarkers are shown to capture the sophisticated nature of the NVU and the glymphatic system, paving the way for a potential route in deconvoluting the complexity associated with the likely interdependence of neurodegenerative and cerebrovascular diseases. The present study is the first, to the best of our knowledge, that casts and implements the 6-MPET equations in a 3D anatomically accurate brain geometry.

Subject-specific multi-poroelastic model for exploring the risk factors associated with the early stages of Alzheimer's disease

There is emerging evidence suggesting that Alzheimer's disease is a vascular disorder, caused by impaired cerebral perfusion, which may be promoted by cardiovascular risk factors that are strongly influenced by lifestyle. In order to develop an understanding of the exact nature of such a hypothesis, a biomechanical understanding of the influence of lifestyle factors is pursued. An extended poroelastic model of perfused parenchymal tissue coupled with separate workflows concerning subject-specific meshes, permeability tensor maps and cerebral blood flow variability is used. The subject-specific datasets used in the modelling of this paper were collected as part of prospective data collection. Two cases were simulated involving male, non-smokers (control and mild cognitive impairment (MCI) case) during two states of activity (high and low). Results showed a marginally reduced clearance of cerebrospinal fluid (CSF)/interstitial fluid (ISF), elevated parenchymal tissue displacement and CSF/ISF accumulation and drainage in the MCI case. The peak perfusion remained at 8 mm s⁻¹ between the two cases.

Contemporary management and surveillance strategy after shunt or endoscopic third ventriculostomy procedures for hydrocephalus

The management of hydrocephalus can be challenging even in expert hands. Due to acute presentation, recurrence, accompanying complications, the need for urgent diagnosis; a robust management plan is an absolute necessity. We devised a novel time efficient surveillance strategy during emergency, and clinic follow up settings which has never been described in the literature. We searched all articles embracing management/surveillance protocol on pediatric hydrocephalus utilizing the terms "hydrocephalus follow up" or "surveillance protocol after hydrocephalus treatment". The authors present their own strategy based on vast experience in the hydrocephalus management at a single institution. The need for the diagnostic laboratory testing, age and presentation based radiological imaging, significance of neuro-opthalmological exam, and when to consider the emergent exploration have been discussed in detail. Moreover, a definitive triaging strategy has been described with the help of flow chart diagrams for clinicians, and the neurosurgeons in practice. The triage starts from detail history, physical exam, necessary labs, radiological imaging depending on the presentation, and the age of the child. A quick head CT scan helps after shunt surgery while, a FAST sequence MRI scan (fsMRI) is important in post ETV patients. The need for neuro-opthalmological exam, and the shunt series stays vital in asymptomatic patients during regular follow up.

Research into the Physiology of Cerebrospinal Fluid Reaches a New Horizon: Intimate Exchange between Cerebrospinal Fluid and Interstitial Fluid May Contribute to Maintenance of Homeostasis in the Central Nervous System

Cerebrospinal fluid (CSF) plays an essential role in maintaining the homeostasis of the central nervous system. The functions of CSF include: (1) buoyancy of the brain, spinal cord, and nerves; (2) volume adjustment in the cranial cavity; (3) nutrient transport; (4) protein or peptide transport; (5) brain volume regulation through osmoregulation; (6) buffering effect against external forces; (7) signal transduction; (8) drug transport; (9) immune system control; (10) elimination of metabolites and unnecessary substances; and finally (11) cooling of heat generated by neural activity. For CSF to fully mediate these functions, fluid-like movement in the ventricles and subarachnoid space is necessary. Furthermore, the relationship between the behaviors of CSF and interstitial fluid in the brain and spinal cord is important. In this review, we will present classical studies on CSF circulation from its discovery over 2,000 years ago, and will subsequently introduce functions that were recently discovered such as CSF production and absorption, water molecule movement in the interstitial space, exchange between interstitial fluid and CSF, and drainage of CSF and interstitial fluid into both the venous and the lymphatic systems. Finally, we will summarize future challenges in research. This review includes articles published up to February 2016.

Investigating cerebral oedema using poroelasticity

Cerebral oedema can be classified as the tangible swelling produced by expansion of the interstitial fluid volume. Hydrocephalus can be succinctly described as the abnormal accumulation of cerebrospinal fluid (CSF) within the brain which ultimately leads to oedema within specific sites of parenchymal tissue. Using hydrocephalus as a test bed, one is able to account for the necessary mechanisms involved in the interaction between oedema formation and cerebral fluid production, transport and drainage. The current state of knowledge about integrative cerebral dynamics and transport phenomena indicates that poroelastic theory may provide a suitable framework to better understand various diseases. In this work, Multiple-Network Poroelastic Theory (MPET) is used to develop a novel spatio-temporal model of fluid regulation and tissue displacement within the various scales of the cerebral environment. The model is applied through two formats, a one-dimensional finite difference - Computational Fluid Dynamics (CFD) coupling framework, as well as a two-dimensional Finite Element Method (FEM) formulation. These are used to investigate the role of endoscopic fourth ventriculostomy in alleviating oedema formation due to fourth ventricle outlet obstruction (1D coupled model) in addition to observing the capability of the FEM template in capturing important characteristics allied to oedema formation, like for instance in the periventricular region (2D model).

Finite element analysis of periventricular lucency in hydrocephalus: extravasation or transependymal CSF absorption?

OBJECTIVE

Periventricular lucency (PVL) is often observed in the hydrocephalic brain on CT or MRI. Earlier studies have proposed the extravasation of ventricular CSF into the periventricular white matter or transependymal CSF absorption as possible causes of PVL in hydrocephalus. However, there is insufficient evidence for either theory to be conclusive.

METHODS

A finite element (FE) model of the hydrocephalic brain with detailed anatomical geometry was constructed to investigate the possible mechanism of PVL in hydrocephalus. The initiation of hydrocephalus was modeled by applying a transmantle pressure gradient (TPG). The model was exposed to varying TPGs to investigate the effects of different geometrical characteristics on the distribution of PVL. The edema map was derived based on the interstitial pore pressure.

RESULTS

The model simulated the main radiological features of hydrocephalus, i.e., ventriculomegaly and PVL. The degree of PVL, assessed by the pore pressure, was prominent in mild to moderate ventriculomegaly. As the degree of ventriculomegaly exceeded certain values, the pore pressure across the cerebrum became positive, thus inducing the disappearance of PVL.

CONCLUSIONS

The results are in accordance with common clinical findings of PVL. The degree of ventriculomegaly significantly influences the development of PVL, but two factors were not linearly correlated. The results are indicative of the transependymal CSF absorption as a possible cause of PVL, but the extravasation theory cannot be formally rejected.

Evaluation of the Production and Absorption of Cerebrospinal Fluid

The traditional hypothesis of cerebrospinal fluid (CSF) hydrodynamics presumes that CSF is primarily produced in the choroid plexus (CP), then flows from the ventricles into the subarachnoid spaces, and mainly reabsorbed in the arachnoid granulations. This hypothesis is necessary to reconsider in view of recent research and clinical observations. This literature review presents numerous evidence for a new hypothesis of CSF hydrodynamics-(1) A significantly strong relationship exists between the CSF and interstitial fluid (IF), (2) CSF and IF are mainly produced and absorbed in the parenchymal capillaries of the brain and spinal cord. A considerable amount of CSF and IF are also absorbed by the lymphatic system, and (3) CSF movement is not unidirectional flow. It is only local mixing and diffusion.

Radiographic evaluation of pediatric cerebrospinal fluid shunt malfunction in the emergency setting

Children with ventricular cerebrospinal fluid shunts for treatment of hydrocephalus require frequent evaluation for potential shunt malfunction. Current practice relies heavily on neuroimaging, particularly cranial computed tomography, which repeatedly exposes children to ionizing radiation. Rapid cranial magnetic resonance imaging is a new radiation-sparing alternative to CT for evaluation of potential shunt malfunction. We review the diagnostic test performance, radiation exposure, advantages, and limitations of the major neuroimaging modalities available to providers caring for children with possible shunt malfunction in the emergent setting.

Porohyperelastic anatomical models for hydrocephalus and idiopathic intracranial hypertension

OBJECT

Brain deformation can be seen in hydrocephalus and idiopathic intracranial hypertension (IIH) via medical images. The phenomenology of local effects, brain shift, and raised intracranial pressure and herniation are textbook concepts. However, there are still uncertainties regarding the specific processes that occur when brain tissue is subject to the mechanical stress of different temporal and spatial profiles of the 2 neurological disorders. Moreover, recent studies suggest that IIH and hydrocephalus may be diseases with opposite pathogenesis. Nevertheless, the similarities and differences between the 2 subjects have not been thoroughly investigated.

METHODS

An anatomical porohyperelastic finite element model was used to assess the brain tissue responses associated with hydrocephalus and IIH. The same set of boundary conditions, with the exception of brain loading for development of the transmantle pressure gradient, was applied for the 2 models. The distribution of stress and strain during tissue distortion is described by the mechanical parameters.

RESULTS

The results of both the hydrocephalus and IIH models correlated with pathological characteristics. For the hydrocephalus model, periventricular edema was associated with the presence of positive volumetric strain and void ratio in the lateral ventricle horns. By contrast, the IIH model revealed edema across the cerebral mantle, including the centrum semiovale, with a positive void ratio and volumetric strain.

CONCLUSIONS

The model simulates all the clinical features in correlation with the MR images obtained in patients with hydrocephalus and IIH, thus providing support for the role of the transmantle pressure gradient and capillary CSF absorption in CSF-related brain deformation. The finite element methods can be used for a better understanding of the pathophysiological mechanisms of neurological disorders associated with parenchymal volumetric fluctuation.

Reassessing cerebrospinal fluid (CSF) hydrodynamics: a literature review presenting a novel hypothesis for CSF physiology

The traditional model of cerebrospinal fluid (CSF) hydrodynamics is being increasingly challenged in view of recent scientific evidences. The established model presumes that CSF is primarily produced in the choroid plexuses (CP), then flows from the ventricles to the subarachnoid spaces, and is mainly reabsorbed into arachnoid villi (AV). This model is seemingly based on faulty research and misinterpretations. This literature review presents numerous evidence for a new hypothesis of CSF physiology, namely, CSF is produced and reabsorbed throughout the entire CSF-Interstitial fluid (IF) functional unit. IF and CSF are mainly formed and reabsorbed across the walls of CNS blood capillaries. CP, AV and lymphatics become minor sites for CSF hydrodynamics. The lymphatics may play a more significant role in CSF absorption when CSF-IF pressure increases. The consequences of this complete reformulation of CSF hydrodynamics may influence applications in research, publications, including osteopathic manual treatments.

Ventricle equilibrium position in healthy and normal pressure hydrocephalus brains using an analytical model

The driving force that causes enlargement of the ventricles remains unclear in case of normal pressure hydrocephalus (NPH). Both healthy and NPH brain conditions are characterized by a low transparenchymal pressure drop, typically 1 mm Hg. The present paper proposes an analytical model for normal and NPH brains using Darcy's and Biot's equations and simplifying the brain geometry to a hollow sphere with an internal and external radius. Self-consistent solutions for the large deformation problem that is associated with large ventricle dilation are presented and the notion of equilibrium or stable ventricle position is highlighted for both healthy and NPH conditions. The influence of different biomechanical parameters on the stable ventricle geometry is assessed and it is shown that both CSF seepage through the ependyma and parenchymal permeability play a key role. Although very simple, the present model is able to predict the onset and development of NPH conditions as a deviation from healthy conditions.

Evans' index revisited: the need for an alternative in normal pressure hydrocephalus

BACKGROUND

The international guidelines for the diagnosis of normal pressure hydrocephalus (NPH) define ventricular enlargement as Evans' index greater than 0.3.

OBJECTIVE

To establish whether there is a correlation between Evans' index and ventricular volume (VV) in NPH and whether choosing different planes for the measurements could produce significantly different results.

METHODS

Pre-shunt insertion, thin-section CT scans of the brains of 10 patients with shunt-responsive NPH were reviewed retrospectively, measuring Evans' index, frontal horn index, VV, and total intracranial volume (ICV). The ventricular/intracranial volume index (VV/ICV) was calculated. Correlation between each of the linear indices and VV and VV/ICV was done.

RESULTS

Significant differences were found in the index values calculated at different planes. The frontal horn index at a plane 16 mm parallel to the anterior commissure-posterior commissure (AC-PC) plane showed best correlation with VV and VV/ICV (r: 0.658 and 0.587, respectively). Evans' index, also obtained at a plane 16 mm parallel to the AC-PC plane, showed best correlation with VV and VV/ICV (r: 0.619 and 0.498, respectively).

CONCLUSION

Evans' index value can vary significantly in a patient with NPH, depending on the level of the brain CT scan image at which the frontal horns and maximal inner skull diameters are measured. Evans' index is not an ideal method for estimating the VV in NPH patients. Volumetric measurements represent the logical accurate estimate of true ventricular size as well as the size of the other intracranial compartments.

Development of hydrocephalus and classical hypothesis of cerebrospinal fluid hydrodynamics: facts and illusions

According to the classical hypothesis of the cerebrospinal fluid (CSF) hydrodynamics, CSF is produced inside the brain ventricles, than it circulates like a slow river toward the cortical subarachnoid space, and finally it is absorbed into the venous sinuses. Some pathological conditions, primarily hydrocephalus, have also been interpreted based on this hypothesis. The development of hydrocephalus is explained as an imbalance between CSF formation and absorption, where more CSF is formed than is absorbed, which results in an abnormal increase in the CSF volume inside the cranial CSF spaces. It is believed that the reason for the imbalance is the obstruction of the CSF pathways between the site of CSF formation and the site of its absorption, which diminishes or prevents CSF outflow from the cranium. In spite of the general acceptance of the classical hypothesis, there are a considerable number of experimental results that do not support such a hypothesis and the generally accepted pathophysiology of hydrocephalus. A recently proposed new working hypothesis suggests that osmotic and hydrostatic forces at the central nervous system microvessels are crucial for the regulation of interstial fluid and CSF volume which constitute a functional unit. Based on that hypothesis, the generally accepted mechanisms of hydrocephalus development are not plausible. Therefore, the recent understanding of the correlation between CSF physiology and the development of hydrocephalus has been thoroughly presented, analyzed and evaluated, and new insights into hydrocephalus etiopathology have been proposed, which are in accordance with the experimental data and the new working hypothesis.

Computational model of the cerebral ventricles in hydrocephalus

Understanding the mechanisms of tissue injury in hydrocephalus is important to shed light on the pathophysiology of this neurostructural disorder. To date, most of the finite element models created to study hydrocephalus have been two-dimensional (2D). This may not be adequate as the geometry of the cerebral ventricles is unique. In this study, a three-dimensional (3D) finite element model of the cerebral ventricles during hydrocephalus is presented. Results from this model show that during hydrocephalus, the periventricular regions experience the highest stress, and stress magnitude is approximately 80 times higher than the cerebral mantle. This suggests that functional deficits observed in hydrocephalic patients could therefore be more related to the damage to periventricular white matter. In addition, the stress field simulated in the tissues based on the 3D model was found to be approximately four times lower than on the 2D model.

The history of mathematical modeling in hydrocephalus

The mathematical modeling of hydrocephalus is a relatively young field. The discipline evolved from Hakim's initial description of the brain as a water-filled sponge. Nagashima and colleagues subsequently translated this description into a computer-driven model by defining five important system rules. A number of researchers have since criticized and refined the method, providing additional system constraints or alternative approaches. Such efforts have led to an increased understanding of ventricular shape change and the development of periventricular lucency on imaging studies. However, severe limitations exist, precluding the use of the mathematical model to influence the operative decisions of practicing surgeons. In this paper, the authors explore the history, limitations, and future of the mathematical model of hydrocephalus.

Computed Tomography in the Diagnosis of Subarachnoid Haemorrhage

Early computed tomography (CT) is very useful in detecting subarachnoid haemorrhage (SAH). It offers a lot of information about the origin, the extent of the haemorrhage and the early complications (hydrocephalus, haematoma).

Moreover, CT scan can suggest the site of bleeding aneurysm and the risk of severe vasospasm.

In some cases, CT shows a perimesencephalic SAH in which often no aneurysm can be detected.

The sensitivity of CT in demonstrating SAH decreases as the time between onset of SAH and CT scanning increases.

White matter changes in normal pressure hydrocephalus and Binswanger disease: specificity, predictive value and correlations to axonal degeneration and demyelination

OBJECTIVES

To analyse the diagnostic and prognostic value of periventricular hyperintensity (PVH) and deep white matter hyperintensity (DWMH) magnetic resonance imaging (MRI) changes and their relation to symptoms and cerebrospinal fluid (CSF) markers of demyelination (sulphatide) and axonal degeneration [neurofilament triplet protein (NFL)] in a large series of patients with normal pressure hydrocephalus (NPH) and Binswanger disease (BD).

MATERIALS AND METHODS

PVH and DWMH were determined by a semi-automatic segmentation method on T2-weighted images in 29 patients with NPH and 17 patients with BD. CSF analyses, psychometric testing and quantification of balance, gait and continence were performed in all patients and also postoperatively in NPH patients.

RESULTS

No MRI variable could identify NPH or BD patients. Abundant PVH and DWMH preoperatively correlated with improvement in gait, balance and psychometric performance after shunt surgery (P < 0.05). CSF sulphatide correlated positively with the amount of DWMH (P < 0.05) while NFL was correlated to both PVH and DWMH (P < 0.05). Abundant PVH correlated with poor psychometric performance while DWMH correlated with gait disturbance (P < 0.05). Postoperative reduction in PVH correlated with improvement in gait, balance and psychometric performance.

CONCLUSION

In spite of a refined quantification method, NPH and BD patients exhibited similar MRI changes. MRI had a predictive value in NPH patients. DWMH might relate to demyelination and PVH to neuronal axonal dysfunction. NPH and BD share the major part of symptoms and MRI changes, indicating a common pathophysiological pattern, and we raise the question of how to treat BD patients.

Ultrasonographic evaluation of infantile hydrocephalus before and after shunting. A study in 20 children

The authors present the results of a prospective study of 20 children with congenital or acquired hydrocephalus of nontumoral etiology and submitted to ventriculo- (or cyst-) peritoneal shunting with valve. The diagnosis was established by B-mode or real-time brain sonography, in association with another neuroradiological procedure (computed tomography, ventriculography with air or Dimer-X, cerebral angiography). Among the proposed measurements (cortical thickness, lateral ventricle height, III ventricle width and ventricular ratio) for pre- and postoperative comparison, the cortical thickness and the lateral ventricle height were the ones that changed significantly when analyzed by sonography. The routine use of brain sonography allowed the visualization of the ventricular catheter position and the diagnosis of complications, such as subdural collection, progressive enlargement of cysts, isolated IV ventricle, etc, even before symptoms arise. The authors conclude that sonography is easily performed, inexpensive and innocuous, and should be used routinely during the follow-up of children with hydrocephalus.

A characteristic ventricular shape in myelomeningocele-associated hydrocephalus? A CT stereology study

We measured the volume of the supratentorial ventricles in 39 consecutive children with myelomeningocele (MMC) and associated hydrocephalus, using a stereological method based on the Cavalieri theorem of systematic sampling. We distinguished the following groups: newborns before and after cerebrospinal fluid shunting (14), a somewhat larger group of newborns with an untreated MMC-associated hydrocephalus (25) and a group of shunted children at a mean age of 1.5 years (28). We paid special attention to the shape of the lateral ventricles, looking separately at the anterior and posterior halves. The measurements were compared with a healthy control group (10) and with children with hydrocephalus unrelated to MMC (15). The average volume ratio of the posterior to the anterior half of the lateral ventricles was 1.05 +/- 0.39 in non-hydrocephalic children, 1.11 +/- 0.55 in untreated hydrocephalic children without MMC, and 2.15 +/- 0.65 in MMC-associated hydrocephalus prior to shunting. These ratios did not change significantly after shunting. This confirms our impression that MMC-associated hydrocephalus shows a characteristic shape, with a disproportionate enlargement of the posterior part of the lateral ventricles, in clear contrast to the normal-width frontal horns. This shape is reminiscent of the fetal ventricular shape. It reveals disturbance of brain development in children with MMC, which goes beyond the classic description of the Chiari malformation.

Infantile hydrocephalus: management using CT assessment

When determining a management plan for infantile hydrocephalus, the determining factor for or against the implantation of a shunt is the degree of ventricular dilatation. The author has devised a standardised method of estimating this, the use of which has been shown to achieve consistently successful results. Dilatation was determined using the ventricular/biparietal (V/BP) ratio from the axial CT scan at the mid-portion of the bodies of the lateral ventricles, showing the greatest ventricular dilatation. According to this method, hydrocephalus was classified into four grades. These were mild (V/BP ratio 0.26-0.40), moderate (V/BP ratio 0.41-0.60), severe (V/BP ratio 0.61-0.90) and extreme (V/BP ratio 0.91-1). A V/BP ratio of less than 0.26 was considered normal. This method appeared to be accurate and reproducible in infants with hydrocephalus including those with asymmetrical and multiloculated ventricular dilatation. In all the patients with mild hydrocephalus, spontaneous regression or stabilisation occurred and their developmental outcome was normal. Patients with moderate and severe hydrocephalus needed a ventricular shunt and the developmental outcome was satisfactory in 87% of the cases. They were functionally normal although 18 had some abnormal neurological signs. In patients with extreme hydrocephalus the developmental outcome following shunting was satisfactory in 31% of the cases. They were functionally normal although four had abnormal neurological signs. This plan of management was used in a total of 144 infants and it proved to be highly successful.(ABSTRACT TRUNCATED AT 250 WORDS)

Information value of magnetic resonance imaging in shunted hydrocephalus

OBJECTIVE

To study the role of magnetic resonance imaging (MRI) in evaluating children with shunted hydrocephalus.

METHODS

Sixty one asymptomatic children with shunted hydrocephalus or cystic cerebrospinal fluid collections were studied by cranial MRI. The information obtained from the images was classified into three categories: provided (1) a new diagnosis, (2) additional information, or (3) no essential new information. The findings were compared with those of the last follow up computed tomograms.

RESULTS

MRI provided a new diagnosis in seven cases (11.5%), and additional information was obtained in 34 (55.7%) cases. In 20 cases (32.8%) no essential new information was obtained. MRI visualised white matter lesions and corpus callosum pathology more often than computed tomograms.

CONCLUSIONS

MRI provided new important information in cases of children with shunted hydrocephalus to such an extent that it can be recommended as the primary imaging method for every child with this disorder.

Hydrocephalus: is impaired cerebrospinal fluid circulation only one problem involved?

Hydrocephalus is a complex disease of the brain as a whole, and imbalance between cerebrospinal fluid (CSF) formation and absorption is not the sole mechanism involved in its pathophysiology. In the absence of a lymphatic system in the central nervous system, open communication between CSF and interstitial fluid (ISF) of the brain may contribute to maintaining homeostasis of the brain, keeping the microchemical environment in good balance. Membranes or cell layers separating CSF from ISF of the brain do not provide impermeability, so the CSF communicates with ISF across the ependymal layer and the pial surface of the brain. In contradiction of the classical theory, the CSF one may obtain at the cisterna magna, for instance, is different from the newly formed CSF out of the choroid plexus, because it has been modified by the free communication between CSF and ISF spaces as the CSF descends along the neural axis. Free flow of water and some smaller molecules provides a bidirectional movement of water and other materials, and this must play an important role in brain volume control. The significance of this role should not be overlooked in regard to the pathophysiology of hydrocephalus.

The value of baseline CT head scans in the assessment of shunt complications in hydrocephalus

The purpose of this study was to determine the value of a baseline CT head scan in the assessment of patients who subsequently presented with symptoms which may have been due to shunt complications (such as blockage or infection). In all these patients the shunt had been inserted in the treatment of hydrocephalus. We conclude that the presence of a baseline scan does not add to the interpretation of CT scans done when the patient presents with symptoms of possible shunt malfunction.

Slit ventricle syndrome in children: clinical presentation and treatment

Symptomatic ventricular coaptation, or the slit ventricle syndrome, is frequently described and recognized as a clinical entity in the pediatric population. It is characterized by symptoms of shunt failure (i.e., ataxia, obtundation, nausea, vomiting, lethargy, irritability, and complaints of headache) and the CT findings of ventricular coaptation (slit-like ventricles). This study of twenty-two children with this syndrome reflects the variety of possible clinical presentations, and the variety of available treatment modalities. Multiple therapeutic approaches were required in seven of the patients. This illustrates not only an evolving treatment regimen, but also that a single treatment modality is not universally effective. Six patients needed only occasional symptomatic support. Blockage and/or removal of the shunt system was the definitive therapy in six patients, pressure augmentation in nine patients, and subtemporal craniectomy in one. This article outlines the theoretical pathophysiology, and a scheme for the management of patients with this syndrome.

Dilatation of the temporal horn in subarachnoid haemorrhage

CT studies of 50 patients with spontaneous subarachnoid haemorrhage (SAH) and 100 randomly selected patients were reviewed with regard to the size of the frontal and temporal horns of the lateral ventricles. The temporal horn was classified into four grades, based on the size of its posterior portion at the level of the midbrain. The horn was clearly visible in 66% of patients with SAH, but in only 2% of controls. In the SAH group, the temporal horn tended to dilate sooner than the frontal horn after haemorrhage and could be seen clearly in a larger proportion of patients. Thus, assessment of the size of the temporal horn appears to be a simple and sensitive method for assessing ventricular dilatation. In addition, dilatation of the temporal horn may prove to be an important indirect sign suggesting SAH in patients in whom no high density clot is seen on CT.

Infantile hydrocephalus: brain sonography as an effective tool for diagnosis and follow-up

Infantile hydrocephalus is a common disease. In most affected children the process starts before the age of 2 when the bregmatic fontanel is still open. Brain sonography has emerged as an effective tool in diagnosing progressive ventricle dilation and may be used for continuous follow-up. It gives such important information as: (a) cortical thickness, an expression of proper shunt function and of prognostic value concerning neuropsychological development; (b) position of the tip of the catheter, which is considered by some to be a predictive factor of shunt failure; (c) other complications such as subdural collections, isolated IV ventricle, and slit ventricles. This methodology permits frequent examinations and allows better comprehension of the pathological process by the parents and medical staff.

Hydrocephalus: overdrainage by ventricular shunts. A review and recommendations

Selected literature review of the clinical course of patients with ventricular shunts for hydrocephalus shows that the effects of cerebrospinal fluid overdrainage are subdural hematoma, craniosynostosis, slit ventricle syndrome, and low intracranial pressure syndrome. These occur sequentially at different age groups, but approximate averages of incidence and time of occurrence after first shunt reveal an overall incidence of 10%-12% for at least one of these appearing at 6.5 years after shunting. The basic etiology, diagnosis, and variety of treatment modalities available are reviewed, including the need for shunt closing intracranial pressure control. Included is a hydrocephalus program designed to minimize the need for long-term extracranial shunts and to maximize therapeutic intracranial procedures for hydrocephalus.

Characterization of periventricular edema in normal-pressure hydrocephalus by measurement of water proton relaxation times

The magnetic resonance longitudinal relaxation time (T1) and transverse relaxation time (T2) of the water proton of the periventricular white and cortical gray matter were measured for 17 control patients and 21 patients with suspected normal-pressure hydrocephalus (NPH). Of the latter group, 14 showed good response to shunting (true-NPH group) and seven showed no response (false-NPH group). In the true-NPH group, both the T1 and the T2 of the periventricular white matter were significantly prolonged compared to the control values, and slowly shortened after cerebrospinal fluid (CSF) shunting. The true-NPH group showed significantly longer T1 and T2 of the white matter than did the false-NPH group. The T1 and T2 of the white matter were longer than those of the gray matter in this group, which was the reverse of the relationship observed in the control patients. In the white matter of the false-NPH group, there was a significant prolongation of T1 only; no difference was seen in the T2 compared to control values. There was no change in either T1 or T2 of this region after CSF shunting. The false-NPH group showed no significant difference in either T1 or T2 between the white and the gray matter. There was no difference in either T1 or T2 of the gray matter between the false-NPH and control groups or between preshunt and postshunt measurements in each patient group. It is suggested that a distinction between true- and false-NPH, which cannot be made from the radiographic appearance alone, may be possible from measurement of relaxation times. The mechanism of varied relaxation behavior between two entities may be explained by a difference in properties of the biological water and its environment.

Comparison of computerized tomography with magnetic resonance imaging (MRI) in the evaluation of encephalic ventricular volume

The volume of the encephalic ventricles was determined from computerized tomographic (CT) and magnetic resonance imaging (MRI) scans of seven subjects without apparent pathology and three subjects with enlarged ventricles. Since there are many conditions in which the encephalic ventricles become enlarged such as Alzheimer's disease and hydrocephalus, accurate measurement of these structures provides (1) a valuable and safe means of aiding in the diagnosis of such conditions and (2) important follow-up information on affected patients. This paper presents the data obtained from the second phase of a three phase study. The first phase demonstrated the possibility of measuring fluid filled spaces by MRI in three phantom preparations (small, medium, and large "ventricles"). The results were compared with those obtained from the computerized tomography (CT) scans of the same preparations. This phase of the study compares the volumes obtained from CT scans with those obtained from MRI scans of the same individuals. The volumetric calculations were done with the aid of a Calcomp 9000 digital analyser programmed to compensate for the scale factor and slice thickness of the images. The results obtained from the MRI scans correlated closely with those obtained from the CT scans of the same subjects. The third and final phase of the project is the development of an MRI volumetric data base for the encephalic ventricles using a larger number of subjects.

Hydrocephalus--revision of its definition and classification with special reference to "intractable infantile hydrocephalus"

With the advent of computed tomography (CT) scan, much information has been obtained about the pathophysiology of hydrocephalus. It is now clear that hydrocephalus is not a disease entity but rather a syndrome or sign resulting from disturbances in the dynamics of cerebralspinal fluid (CSF) caused by various diseases. Consequently, it has become necessary to revise its definition and classification. In this paper, a contemporary definition and classification of hydrocephalus are presented. Also, a classification of "intractable hydrocephalus"--with its diagnostic criteria--which is a clinically unsolved problem, is attempted, bearing in mind its place in the clinical management and future investigation of the pathophysiology of hydrocephalus.

Cranial ultrasonography in the evaluation of macrocrania in infancy

Cranial ultrasonography was used in the initial evaluation of 40 infants with macrocrania. Three of the infants had normal findings. The other 37 had evidence of various types of abnormality: intraventricular obstructive hydrocephalus, external hydrocephalus, arrested hydrocephalus with atrophy, or mild ventriculomegaly. All the infants were given neurological and developmental examinations at the time of presentation and were followed up for one year. Sonograms and head-circumference and intracranial pressure measurements were done at intervals, according to the initial ultrasound findings and the clinical status of the children. Neurodevelopmental outcome was related to the type of abnormality. The majority of children with external hydrocephalus were neurodevelopmentally normal at follow-up. In contrast, those with obstructive or arrested hydrocephalus had unfavourable outcomes, which may be related to the significant perinatal insult causing the hydrocephalus. CT confirmation was available for 16 of the infants.

Magnetic resonance imaging of silastic-induced canine hydrocephalus

Nine adult beagle dogs underwent magnetic resonance imaging in a 2-Tesla small-bore unit. Six surviving dogs were followed up serially with magnetic resonance imaging after induction of hydrocephalus by injection of Silastic into the prepontine cistern or fourth ventricle. Ventricular size (Y) measured as percentage cross-sectional area of an anterior frontal slice was related to postoperative day (X) as Y = 1.54 + 4.21 x ln(X), r = 0.9596. Periventricular edema appeared initially in the superlateral angles of the frontal horns in an area that corresponded histologically to the subcallosal fasciculus. T1 relaxation time of normal white matter of 979.32 msec increased to 1813.90 msec in the area of the edema (p less than 0.0001). The T2 relaxation time of normal white matter of 83.39 msec increased to 238.26 msec in the area of the edema (p less than 0.0001). Histological changes included expansion of the extracellular space in an area comparable to the region of increased signal intensity on T2-weighted images, as well as diffuse astrocytosis in the chronically hydrocephalic dogs.

MRI and hydrocephalus in childhood

In six young patients presenting with raised intracranial pressure during the period of a year, CT revealed the presence of hydrocephalus, but not the cause. Magnetic Resonance Imaging not only showed the site and nature of the obstructing lesion, but also detected additional clinically silent spinal cord tumors in five of the patients. The place of MRI in the diagnosis of diseases involving the region of the cranio-cervical junction and in the elucidation of "unexplained hydrocephalus" is considered.

Ventricular shunt functioning despite extraventricular location of the catheter tip as revealed by computed tomography

Two cases of infantile hydrocephalus are reported, in which the ventricular shunt proved to function despite the catheter tip being located outside the ventricular system, as revealed by computed tomography. This condition could be erroneously diagnosed as arrested hydrocephalus or proximal shunt malfunction, with a resultant potential risk of inadequately removing the catheter.

Postoperative subdural fluid collections in neurosurgery

After introduction of computed tomography (CT) scanning, subdural fluid collections (SFCs) have been more frequently detected. We encountered 1013 operated cases in which CT scans were performed at an early postoperative stage. Postoperative SFC occurred in 165 of the 1013 operated cases (17%). The incidence of SFC was highest in aneurysm surgery (47%), followed by neurovascular decompression (27%) and brain tumor surgery (22%). In aneurysm surgery, preoperative ventricular dilatation seemed to promote the occurrence of SFC. In tumor surgery, SFC occurred more frequently when the tumor existed in the sellar region. The SFCs decreased or disappeared in most cases on sequential CT scans, but increased in 27 cases. In the latter, maximum thickness of the SFC was seen between 20 and 30 postoperative days. Nineteen of the 27 cases had preoperative ventricular dilatation. Operation for SFC was performed in four cases with clinical symptoms and signs. Three of 169 cases developed into chronic subdural hematomas.

Neurosonography of hydrocephalus in infants

Transfontanel cranial ultrasonography reliably delineates ventricular size and anatomy in small infants. In these children, it is an excellent primary imaging technique for evaluation of the many clinical problems related to ventricular dilatation. Sonography can be useful for: detecting ventriculomegaly, differentiating nonobstructive ventricular dilatation from obstructive enlargement (hydrocephalus), determining the cause of hydrocephalus; aiding in the temporary management of patients with hydrocephalus; and aiding in the management of patients with permanent ventricular shunts.

The value of immediate post-operative routine CT related to uncomplicated ventricle drainage in childhood hydrocephalus

Retrospectively we assessed the value of routine postoperative CT scans in 113 children shunted for hydrocephalus. Of the 165 routine CT scans 13 showed fortuitous findings (= 8%) with a change in treatment accompanied by questionable benefits in only 2 (= 1.3%). Therefore we suggest that post-operative CT should not be performed as a routine examination but only on clinical grounds.

Pediatric brain computed tomography

Computed tomography today provides good anatomic depiction of the brain and its gross disease processes that have as a manifestation alteration of brain density, disturbance in blood-brain barrier, or mass effect. As such, computed tomography often provides valuable diagnostic information in the appropriate clinical setting. This article reviews many of the more common pediatric central nervous system disease states that have been demonstrated more easily as a result of computed tomography.

Classification and management of the slit ventricle syndrome

A total of 32 patients with overdrainage of CSF, fulfilling the radiological and clinical criteria for collapsed ventricles ("slit ventricles"), were classified into acute, subacute and chronic forms. The basis of classification into these categories was neurologic symptomatology. The majority (29 patients) originally had a ventriculoatrial shunt and 3 had ventriculoperitoneal shunts. Operative correction was performed in 23 patients (insertion of a high pressure valve in 18 and an antisiphon device in 5). Of these, 5 had acute, 10 subacute, and 6 chronic symptoms. Two patients without symptoms were operated on also. During the follow-up period, which varied from 2 to 11 months, no patient has shown recurrence of the original symptoms of the slit ventricle syndrome; two patients developed subacute signs and an antisiphon device was inserted in addition to the high-resistance valve. On the basis of this series, it is concluded that the slit ventricle syndrome can also develop in patients with an atrioventricular shunt and can be treated by preventing further overdrainage of CSF. Though the results are acceptable by present methods, the need for a servo-regulated shunt persists. The surgical correction should preferably be performed before the acute phase. A flowchart is presented for management of a child with suspected slit ventricles.

Cerebrospinal fluid and extracellular fluid: their relationship to pressure and duration of canine hydrocephalus

Fifteen greyhound dogs were made hydrocephalic by the transsphenoidal injection of silicone into the basal cisterns at the level of the tentorial incisura. Six of these animals had ventriculocisternal perfusions 4 weeks later and six at 8 weeks, half at 150 and half at 100 mm H2O. Three 12-week dogs were perfused at 150 mm H2O. Serial sections of brain from the ependyma of the left frontal horn to the overlying pia were counted for 14C inulin and 3H methotrexate uptake. Tissue concentrations of both markers varied indirectly with distance from ependyma and from pia, and varied directly with perfusion pressure. The data indicate that the diffusional pathway between cerebrospinal fluid (CSF) and extracellular fluid (ECF) can be modified by CSF pressure changes, i.e., CSF flows from the ventricles and subarachnoid space into the extracellular space when CSF pressures are raised. Brain uptake of inulin and methotrexate was significantly increased in the dogs made hydrocephalic 4 weeks prior to perfusion, but was less so in the 8-week hydrocephalics. Uptake of the tracers in three 12-week animals was similar to that found previously in normal dogs at elevated pressures. These findings correspond in location and time to the periventricular lucencies that are seen by computed tomography in human subacute hydrocephalus. They are apparently due to pressure-related changes in the volume of the ECF.

Computed tomography of the "armored brain"

A calcified chronic subdural hematoma may cover the surface of the cerebral hemispheres to such an extent that one can talk of an "armored brain". Pathogenesis, clinical course and treatment are discussed based on the computed tomograms of five cases.