Effect of non-linear permeability in a spherically symmetric model of hydrocephalus.

We examine a spherically symmetric model of the brain and apply non-linear permeability in a small strain poroelastic framework. Numerical solutions to the model show that non-linear effects tend to improve predictions of ventricle wall displacement and pressure increase in acute hydrocephalus in comparison with a constant permeability model. Our model is used to study different mechanisms for hydrocephalus: complete blockage of the aqueduct and normal pressure hydrocephalus (NPH), as well as offering observations on mechanical effects in idiopathic intracranial hypertension. In each situation it is possible to apply different parameter conditions to quantify mechanical effects that correspond to some observed symptoms. The results support and quantify ideas from Levine (2000, Ventricle size in pseudotumor cerebri and the theory of impaired CSF absorption. J. Neurol. Sci., 177, 85-94) on a poroelastic mechanism for some features of NPH and idiopathic intracranial hypertension.     

New experimental model of acute aqueductal blockage in cats: Effects on cerebrospinal fluid pressure and the size of brain ventricles

It is generally assumed that cerebrospinal fluid (CSF) is secreted in the brain ventricles, and so after an acute blockage of the aqueduct of Sylvius an increase in the ventricular CSF pressure and dilation of isolated ventricles may be expected. We have tested this hypothesis in cats. After blocking the aqueduct, we measured the CSF pressure in both isolated ventricles and the cisterna magna, and performed radiographic monitoring of the cross-sectional area of the lateral ventricle. The complete aqueductal blockage was achieved by implanting a plastic cannula into the aqueduct of Sylvius through a small tunnel in the vermis of the cerebellum in the chloralose-anesthetized cats. After the reconstitution of the occipital bone, the CSF pressure was measured in the isolated ventricles via a plastic cannula implanted in the aqueduct of Sylvius and in the cisterna magna via a stainless steel cannula. During the following 2 h, the CSF pressures in the isolated ventricles and cisterna magna were identical to those in control conditions. We also monitored the ventricular cross-sectional area by means of radiography for 2 h after the aqueductal blockage and failed to observe any significant changes. When mock CSF was infused into isolated ventricles to imitate the CSF secretion, the gradient of pressure between the ventricle and cisterna magna developed, and disappeared as soon as the infusion was terminated. However, when mock CSF was infused into the cisterna magna at various rates, the resulting increased subarachnoid CSF pressure was accurately transmitted across the brain parenchyma into the CSF of isolated ventricles. The lack of the increase in the CSF pressure and ventricular dilation during 2 h of aqueductal blockage suggests that aqueductal obstruction by itself does not lead to development of hypertensive acute hydrocephalus in cats.     

Experimental Spinal Stenosis in Cats: New Insight in Mechanisms of Hydrocephalus Development

In our new experimental model of cervical stenosis without inflammation we have tested hypothesis that cranio‐spinal communication impairment could lead to hydrocephalus development. Spinal and cranial cerebrospinal fluid (CSF) space separation was obtained with positioning of plastic semiring in epidural space at C2 level in cats. Brain ventricles planimetry, and CSF pressure recording in lateral ventricle (LV) and lumbar subarachnoid space (LSS) were performed in acute and subchronic experiments. In all experiments opening CSF pressures were normal. However, in acute experiments, an infusion of artificial CSF into the LV led to increase of CSF pressure and significant gradient pressure development between LV and LSS due to limited pressure transmission. After 3 or 6 weeks spinal cord atrophy was observed at the site of cervical stenosis, and pressure transmission from LV to LSS was improved as a consequence of spinal tissue atrophy. Planimetry of both the coronal brain slices and the ventricles’ surface showed that control ventricular surface was 0.6 ± 0.1% (n = 5), and 1.6 ± 0.2% (n = 4) in animals with subchronic cervical stenosis (P < 0.002). These results support the mentioned hypothesis claiming that CSF volume cranio‐spinal displacement impairment could start pathophysiological processes leading to development of hydrocephalus.     

A model of in-vivo hydrocephalus shunt dynamics for blockage and performance diagnostics.

The accumulation of excess cerebrospinal fluid in the ventricles of the brain results in hydrocephalus, a condition that is fatal if left untreated. The usual remedy is to insert a shunt into the ventricles of the brain, which drains excess fluid away, moderated by a pressure dependent valve. It is important that the system functions properly so that a reasonable intracranial pressure is maintained. Unfortunately, pressure measurements in the ventricles are highly invasive, while pressure measurements in the shunt outside the skull may not detect any blockage in the catheter inside. Here we develop a model primarily aimed at detecting in vivo a blockage and other shunt malfunction using non-invasive measurements, so that shunt valves can be adjusted accordingly. The system offers a clear insight into how currently available clinical measurements may be utilized. We then extend this to investigate the phenomenon of 'chatter' (rapid opening and closing) and other mechanisms including intracranial pressure pulsatility. Although simple, the model offers a clear indication of what is required for successful regulation of both intracranial pressure and shunt flow.     

Energy harvesting from cerebrospinal fluid pressure fluctuations for self-powered neural implants

In this paper, a novel method to generate electrical energy by converting available mechanical energy from pressure fluctuations of the cerebrospinal fluid within lateral ventricles of the brain is presented. The generated electrical power can be supplied to the neural implants and either eliminate their battery need or extend the battery lifespan. A diaphragm type harvester comprised of piezoelectric material is utilized to convert the pressure fluctuations to electrical energy. The pressure fluctuations cause the diaphragm to bend, and the strained piezoelectric materials generate electricity. In the framework of this study, an energy harvesting structure having a diameter of 2.5 mm was designed and fabricated using microfabrication techniques. A 1:1 model of lateral ventricles was 3D–printed from raw MRI images to characterize the harvester. Experimental results show that a maximum power of 0.62 nW can be generated from the harvester under similar physical conditions in lateral ventricles which corresponds to energy density of 12.6 nW/cm². Considering the available area within the lateral ventricles and the size of harvesters that can be built using microfabrication techniques it is possible to amplify to power up to 26 nW. As such, the idea of generating electrical energy by making use of pressure fluctuations within brain is demonstrated in this work via the 3D–printed model system.     

Hypothesis for lateral ventricular dilatation in communicating hydrocephalus: new understanding of the Monro-Kellie hypothesis in the aspect of cardiac energy transfer through arterial blood flow

Many theories have been postulated to date regarding mechanisms involved in non-enlargement of the subarachnoid space and enlargement of the ventricles in patients with communicating hydrocephalus, but none have been prove to be definite. Cerebrospinal fluid (CSF) movement is known not to bulk flow but rather pulsatile flow that develops from the energy of the blood flow ejected from the heart, in an isolated system of the intracranial cavity surrounded by a solid skull, as in the Monro-Kellie hypothesis. The authors attempt to explain the mechanisms involved in selective enlargement of the lateral ventricle in patients with communicating hydrocephalus by re-addressing the Monro-Kellie hypothesis with respect to cardiac energy transfer and dissipation by the Windkessel effect. The authors present a concept whereby the large energy of blood flow from the heart that is conveyed to the intracranial artery, arteriole, brain parenchyme, ventricle, and CSF within the confined cranial space as in the Monro-Kellie hypothesis, and which ultimately dissipates to maintain an intracranial energy equilibrium. In the same context, if, for some reason the intracranial equilibrium in the energy transfer and dissipation is changed or disrupted, then structural changes would have to occur to achieve and maintain a new intracranial equilibrium. We postulate that the above described mechanisms are those responsible for the development enlarged of lateral ventricles in patients with communicating hydrocephalus. Structural enlargement of the lateral ventricles in communicating hydrocephalus is a consequence of CSF pathway obstruction and resultantly increased CSF absorption function in the lateral ventricle which markedly increases the pulsatile CSF energy flow returning to the lateral ventricles, thus causing collision of pulsatile CSF flow with the brain parenchyme at the ventricular wall, which subsequently leads to structural enlargement of the lateral ventricles. Also, the collision between the CSF pulsation and brain parenchyme pulsation reduces the Windkessel effect of the brain parenchyme which increases the intracranial artery pulse pressure, which in turn is transmitted to the CSF and increases CSF pulse pressure. This vicious circle results in the high pulse pressure within the lateral ventricle structurally dilating the lateral ventricle. Our theory also explains the relationship between ventricle dilatation and idiopathic intracranial hypertension, venous sinus thrombosis, achondroplasia.     

MRI 3D lateral cerebral ventricles in living humans: morphological and morphometrical age-, gender-related preliminary study

Morphological and volumetric variabilities of lateral ventricles are considered indirect indicators of age-and gender-related reductions of white and gray matter. However, no studies have classified lateral ventricles with different morphologies or showed its asymmetric shapes in healthy subjects. We performed an analysis on living subjects, using 3D volume rendering techniques. Eighty-five healthy Caucasian volunteers (49 women and 36 men aged 19–69 years) were scanned by a Philips Achieva 3T R2.6. Three-dimensional reconstruction allowed us to identify three main morphological shapes in living subjects and to show asymmetries between horns. We also assessed the surface deformation of the cerebral ventricles to identify region-specific shape differences in aging healthy adults. Statistical analysis showed significant gender- and age-related volume differences. An increase in lateral ventricle volume appears to be a constant, linear function of age throughout adult life.     

Neuroepithelial and ependymal changes in HTX rats with congenital hydrocephalus: An ultrastructural and immunohistochemical study

To Investigate the pathogenesis of congenital hydrocephalus the brains of HTX rats aged between 16 days and 4 weeks and the brains of normal Wlstar rats of the same ages were examined. In the fetal HTX rat brains, the lateral ventricles were symmetrically dilated from 20 days of gestation. The neuroeplthelium bordering the ventricles showed thinning with cellular disarrangement and deformity. Similar neuroepithelial abnormalities were also found in the lateral ventricles of the HTX rat brain with no macroscopic signs of hydrocephalus at 20 days of gestation. The neuroepithelium showed flattening of the cells, widening of the intercellular spaces, formation of microvilli on the detached lateral cell surfaces, and frequent macrophage infiltration. On the other hand, the neuroepithelial cells of the third ventricle and the aqueduct were affected less severely or showed no significant abnormalities. Immunohistochemlcally, most of the neuroepithelium and ependyma of the lateral ventricles were positive for vimentin in both prenatal and postnatal hydrocephalic HTX rats, while a small number or none of those in normal control rats were positive. These morphological changes suggested that preferential involvement of the lateral ventricular neuroepithelium might be closely associated with the pathogenesis of congenital hydrocephalus in HTX rats.     

Cerebrospinal Fluid Flow Dynamics in the Central Nervous System

Cine-phase-contrast-MRI was used to measure the three-dimensional cerebrospinal fluid (CSF) flow field inside the central nervous system (CNS) of a healthy subject. Image reconstruction and grid generation tools were then used to develop a three-dimensional fluid–structure interaction model of the CSF flow inside the CNS. The CSF spaces were discretized using the finite-element method and the constitutive equations for fluid and solid motion solved in ADINA-FSI 8.6. Model predictions of CSF velocity magnitude and stroke volume were found to be in excellent agreement with the experimental data. CSF pressure gradients and amplitudes were computed in all regions of the CNS. The computed pressure gradients and amplitudes closely match values obtained clinically. The highest pressure amplitude of 77 Pa was predicted to occur in the lateral ventricles. The pressure gradient between the lateral ventricles and the lumbar region of the spinal canal did not exceed 132 Pa (~1 mmHg) at any time during the cardiac cycle. The pressure wave speed in the spinal canal was predicted and found to agree closely with values previously reported in the literature. Finally, the forward and backward motion of the CSF in the ventricles was visualized, revealing the complex mixing patterns in the CSF spaces. The mathematical model presented in this article is a prerequisite for developing a mechanistic understanding of the relationships among vasculature pulsations, CSF flow, and CSF pressure waves in the CNS.     

Correlation between formation of the calcarine sulcus and morphological maturation of the lateral ventricle in cynomolgus monkey fetuses

In the present study developmental changes in the cerebral sulci and volumes of subcortical and archicortical structures of the cerebrum in cynomolgus monkey fetuses were examined with T(1)-weighted magnetic resonance (MR) images in 3D. On the embryonic day (ED) 90, the lateral ventricle had still an immature vesicular shape in the occipital region of the cerebrum, and it dramatically closed its lumen by ED 100. In that period the calcarine sulcus progressively infolded from the medial surface of the cerebral hemisphere narrowing the lumen of the lateral ventricle in the occipital region. Volume of the lateral ventricle decreased in the period ED 90-100, increasing afterwards in spite of increasing volumes of subcortical and archicortical structures such as the caudate nucleus, putamen, globus pallidus, amygdala and hippocampal formation. During the same time, the volume of the germinal matrix around lateral ventricles decreased to disappear completely by ED 120. These results suggest that the morphological maturation of lateral ventricle is linked to the development of calcarine sulcus in cynomolgus monkey fetuses. The degree of infolding of calcarine sulcus on ED 100 would be useful as a gross anatomical landmark for evaluating the cerebral maturation in cynomolgus monkey fetuses.     

Primary intra-axial leiomyosarcoma with obstructive hydrocephalus in a young dog

A female Chihuahua dog aged 2 months had a 3-week history of progressive neurological signs (abnormal behaviour, disorientation, left-sided circling, and incessant whimpering). Necropsy revealed a primary leiomyosarcoma in the midline of the posterior thalamus with secondary obstructive hydrocephalus of the lateral ventricles. Grossly, an infiltrative, grey-white tumour had partly invaded the third ventricle. Histologically, the tumour formed hypercellular, interlacing bundles of neoplastic spindle cells with blunt-ended nuclei. Neoplastic cells were strongly immunoreactive for vimentin and both muscle-specific and alpha-smooth muscle actin; MIB-1 immunoreactivity indicated a proliferative index of up to 5%. Leiomyosarcoma should be included in the differential diagnosis for primary brain tumours and hydrocephalus in young dogs.     

Normal and Hydrocephalic Brain Dynamics: The Role of Reduced Cerebrospinal Fluid Reabsorption in Ventricular Enlargement

CINE phase-contrast MRI (CINE-MRI) was used to measure cerebrospinal fluid (CSF) velocities and flow rates in the brain of six normal subjects and five patients with communicating hydrocephalus. Mathematical brain models were created using the MRI images of normal subjects and hydrocephalic patients. In our model, the effect of pulsatile vascular expansion is responsible for pulsatile CSF flow between the cranial and the spinal subarachnoidal spaces. Simulation results include intracranial pressure gradients, solid stresses and strains, and fluid velocities throughout the cranio-spinal system. Computed velocities agree closely with our in vivo CINE-MRI CSF flow measurements. In addition to normal intracranial dynamics, our model captures the transition to acute communicating hydrocephalus. By increasing the value for reabsorption resistance in the subarachnoid villi, our model predicts that the poroelastic parenchyma matrix will be drained and the ventricles enlarge despite small transmantle pressure gradients during the transitional phase. The poroelastic simulation thus provides a plausible explanation on how reabsorption changes could be responsible for enlargement of the ventricles without large transmantle pressure gradients.     

Three-dimensional fibril-reinforced finite element model of articular cartilage

Collagen fiber orientations in articular cartilage are tissue depth-dependent and joint site-specific. A realistic three-dimensional (3D) fiber orientation has not been implemented in modeling fluid flow-dependent response of articular cartilage; thus the detailed mechanical role of the collagen network may have not been fully understood. In the present study, a previously developed fibril-reinforced model of articular cartilage was extended to account for the 3D fiber orientation. A numerical procedure for the material model was incorporated into the finite element code ABAQUS using the “user material” option. Unconfined compression and indentation testing was evaluated. For indentation testing, we considered a mechanical contact between a solid indenter and a medial femoral condyle, assuming fiber orientations in the surface layer to follow the split-line pattern. The numerical results from the 3D modeling for unconfined compression seemed reasonably to deviate from that of axisymmetric modeling. Significant fiber orientation dependence was observed in the displacement, fluid pressure and velocity for the cases of moderate strain-rates, or during early relaxation. The influence of fiber orientation diminished at static and instantaneous compressions.     

神经内镜下侧脑室手术入路的应用解剖

目的研究神经内镜下侧脑室、第三脑室的重要解剖学结构,为神经内镜下治疗脑室病变提供应用解剖学基础。方法对10具成人尸头分别采用冠状缝前侧脑室前角、三角区及后角3种入路在神经内镜下观察脑室结构并测量数据。结果 (1)侧脑室前角入路可清晰显示侧脑室前角和体部,室间孔的Y形结构,且可以通过室间孔进入第三脑室。(2)冠状缝前穿刺点到侧脑室、室间孔距离为(28.7±2.6)mm、(55.1±2.8)mm,侧脑室前角到室间孔距离为(30.8±2.3)mm,室间孔长、宽径为(5.6±1.4)mm、(3.2±1.1)mm,中间块长径、宽径为(6.3±1.8)mm、(3.4±1.2)mm。(3)侧脑室后角及三角区入路可以观察到侧脑室体部结构及脉络丛。结论 (1)冠状缝前侧脑室前角入路是处理侧脑室、室间孔区及第三脑室病变的理想入路;(2)侧脑室后角入路是治疗侧脑室后角及三角区病变的理想入路;(3)侧脑室三角区入路应用价值低。     

Ultimate test bench for pediatric biventricular assist device based on artificial muscles

Ventricular assist devices (VADs) are used in treatment for terminal heart failure or as a bridge to transplantation. We created biVAD using the artificial muscles (AMs) that supports both ventricles at the same time. We developed the test bench (TB) as the in vitro evaluating system to enable the measurement of performance. The biVAD exerts different pressure between left and right ventricle like the heart physiologically does. The heart model based on child's heart was constructed in silicone. This model was fitted with the biVAD. Two pipettes containing water with an ultrasonic sensor placed on top of each and attached to ventricles reproduced the preload and the after load of each ventricle by the real-time measurement of the fluid height variation proportionally to the exerted pressure. The LabVIEW software extrapolated the displaced volume and the pressure generated by each side of our biVAD. The development of a standardized protocol permitted the validation of the TB for in vitro evaluation, measurement of the performances of the AM biVAD herein, and reproducibility of data.     

主动脉出口血压对左心室血流特性的影响

采用Mimics对心脏进行三维重构,用3-matic进行模型优化以及模型误差分析,对左心室室壁运动做速度分布假设,基于UDF宏文件对左心室室壁运动编写程序,将血液视为非牛顿流体,采用动网格技术研究不同血压对左心室血液流动的影响。模拟发现当左心室收缩时,压力梯度明显,内部压力减小。当左心室舒张时,内部压力逐渐增高。二尖瓣口处的速率先增大后减小。血压升高,左心室内剪切应力持续增大,极易破坏红细胞结构,产生溶血现象,导致心脏功能紊乱。     

Autosomal recessive hydrocephalus with third ventricle obstruction

Here we report a brother and sister who presented in the neonatal period with hydrocephalus. Ultrasonography showed marked dilatation of the lateral ventricles but not the third ventricle. One child with postnatal onset was shunted and had normal development at 3 years. The other child had severe hydrocephalus at birth and was not treated. Neuropathologic studies demonstrated dilatation of the lateral ventricles and marked narrowing of the posterior part of the third ventricle but no other malformations other than those that result directly from hydrocephalus. The potential for a good prognosis is emphasized.     

Ventricular system and choroid plexuses of the human brain during the embryonic period proper

This morphological study, based on serial sections and graphic reconstructions at 4–8 postovulatory weeks (stages 11–23), is believed to be the first account of the ventricular system in staged human embryos. Closure of the caudal neuropore at stage 12 heralds the onset of the ventricular system and separates the ependymal from the amniotic fluid. After the appearance of the optic ventricle at stage 11, the cavity of the telencephalon medium is discernible at stage 13. At stage 14 the future cerebral hemispheres and lateral ventricles begin, and the rhomboid fossa becomes apparent. The medial and lateral ventricular eminences cause indentations in the lateral ventricle by stage 15. The hypothalamic sulcus is evident at stage 16. At stages 17–18 the interventricular foramina are becoming relatively smaller, and cellular accumulations indicate the future choroid villi of the fourth and lateral ventricies. The areae membranaceae rostralis and caudalis are visible in the roof of the fourth ventricle at state 18, and the paraphysis is appearing. At stage 19 choroid villi are seen in the fourth ventricle, and a mesencephalic evagination (Blindsack) is detectable. Choroid villi are noticeable in the lateral ventricle at state 20. An olfactory ventricle is present by stage 21. At about stages 21–23 the lateral ventricle has become C -shaped, so that anterior and inferior horns are visible. Several recesses, e.g., the optic, infundibular, and pineal, develop in the third ventricle during the embryonic period. Features of the ventricular system that do not become apparent until the fetal period include the posterior horn of the lateral ventricle, choroid plexus of the third ventricle, suprapineal recess, interthalamic adhesion, aqueduct, and apertures in the roof of the fourth ventricle.     

Congenital hydrocephalus associated with anomalies of midline telencephalic structures. A case report.

Hydrocephalus is classified into communicating, if cerebrospinal fluid (CSF) can flow freely from the ventricle to the subarachnoid space, and into non-communicating, if it cannot. The cause of hydrocephalus is diverse, either congenital or acquired conditions causing obstruction to the flow of CSF. The location of the lesion is more important than the size or nature of the lesion. We describe an unusual case of congenital communicating hydrocephalus associated with multiple malformations of midline telencephalic structures. This was a premature male baby of 30 weeks gestational age. The pregnancy was terminated after revealing a hydrocephalus by ultrasonography. The cerebral hemispheres showed marked thinning of parenchyme with dilated lateral ventricles, communication of lateral and third ventricles with dilated foramina of Monro, absence of the septum pellucidum, and hypoplasia or focal agenesis of posterior portion of corpus callosum with dorsal dilation of the third ventricle. The right fornix appeared as a single thick midline cord in its approximately normal position and the hippocampi were poorly developed, especially in the left side. The left fornix was rudimentary.