Nonlinear poroplastic model of ventricular dilation in hydrocephalus

Impact of thermodynamical rotational flow of cerebrospinal fluid in the presence of elasticity

OBJECTIVE

To explore the experimental justification of cerebrospinal fluid (CSF) amplitude and elastic fluctuations of ventricles, we extend our previous computational study to models with rotational flow and suitable boundary conditions. In the present study, we include an elastic effect due to the interaction with the thermal solutal model which accounts for CSF motion which flows rotationally due to hydrocephalus flows within the spinal canal.

METHODS

Using an analytical pertubation method, we have attempted a new model to justify CSF flow movement using the influences of wall temperature difference.

RESULTS

This paper presents results from a computational study of the biomechanics of hydrocephalus, with special emphasis on a reassessment of the parenchymal elastic module. CSF amplitude in hydrocephalus patients is 2.7 times greater than that of normal subjects.

CONCLUSIONS

This finding suggests a non-linear mechanical system to present the hydrocephalic condition using a numerical model. The results can be useful to relieve the complexities in the mechanism of hydrocephalus and can shed light to support clinically for a convincing simulation.

Ventricular shape evaluation on early ultrasound predicts post-hemorrhagic hydrocephalus

BACKGROUND

To compare the ability of ventricular morphology on cranial ultrasound (CUS) versus standard clinical variables to predict the need for temporizing cerebrospinal fluid drainage in newborns with intraventricular hemorrhage (IVH).

METHOD

This is a retrospective study of newborns (gestational age <29 weeks) diagnosed with IVH. Clinical variables known to increase the risk for post-hemorrhagic hydrocephalus were collected. The first CUS with IVH was identified and a slice in the coronal plane was selected. The frontal horns of the lateral ventricles were manually segmented. Automated quantitative morphological features were extracted from both lateral ventricles. Predictive models of the need of temporizing intervention were compared.

RESULTS

Sixty-two newborns met inclusion criteria. Fifteen out of the 62 had a temporizing intervention. The morphological features had a better accuracy predicting temporizing interventions when compared to clinical variables: 0.94 versus 0.85, respectively; p < 0.01 for both. By considering both morphological and clinical variables, our method predicts the need of temporizing intervention with positive and negative predictive values of 0.83 and 1, respectively, and accuracy of 0.97.

CONCLUSION

Early cranial ultrasound-based quantitative ventricular evaluation in premature newborns can predict the eventual use of a temporizing intervention to treat post-hemorrhagic hydrocephalus. This may be helpful for early monitoring and treatment.

Negative-Pressure Hydrocephalus: A Case Report on Successful Treatment Under Intracranial Pressure Monitoring with Bilateral Ventriculoperitoneal Shunts

BACKGROUND

Negative-pressure hydrocephalus (NegPH), a very rare condition of unknown etiology and optimal treatment, usually presents postneurosurgery with clinical and imaging features of hydrocephalus, but with negative cerebrospinal fluid pressure.

CASE DESCRIPTION

We describe a NegPH case of -3 mm Hg intracranial pressure that was successfully treated to achieve 5 mm Hg under continuous intracranial pressure monitoring with horizontal positioning, head down and legs elevated to 10°-15°, neck wrapping for controlled venous drainage, chest and abdomen bandages, infusion of 5% dextrose fluid to lower plasma osmolarity (Na⁺, 130-135 mmol/L), daily cerebrospinal fluid drainage >200 mL, and arterial blood gas partial pressure of carbon dioxide >40 mm Hg.

Deformation of the corona radiata and internal capsule in normal pressure hydrocephalus

BACKGROUND AND PURPOSE

The pathophysiology of the clinical manifestations in normal pressure hydrocephalus (NPH) remains obscure. Ventricular dilatation could generate forces on the paracentral fibers of the corona radiata (CR), hence interfering with their function and producing the classical clinical triad. The analysis of the regional displacement and deformation of the white matter bundles, forming the corona radiata and internal capsule, may clarify the relationship between ventricular dilatation and clinical manifestations in NPH.

METHOD

An experimental finite element (FE) analysis was used to simulate ventricular dilatation in 3 dimensions (3D) and to calculate the strain and deformation on the surrounding parenchyma. Magnetic resonance diffusion tensor imaging-based white matter tractography was then applied to retrieve the displacement and deformation exerted along various fiber bundles of the corona radiata and internal capsule. Anterior and posterior limb displacements and elongations were compared using a paired samples t-test.

RESULTS

The internal capsule, hence the corona radiata, of each cerebral hemisphere was segmented into anterior and posterior limbs. Mean displacements and elongations were calculated for each limb. Mean displacement was significantly larger in the anterior limb whereas mean deformation was larger in the posterior limb (P<0.01).

CONCLUSION

The present simulation demonstrates that ventricular dilatation does not have a homogeneous effect on the periventricular fibre tracts, with a particular load on the corticospinal tract. The affection of this tract remains thereby a potential factor in the generation of the NPH gait disorders.

Patient-specific biomechanical modeling of ventricular enlargement in hydrocephalus from longitudinal magnetic resonance imaging

Ogden type of hyperelastic constitutive law has recently emerged in modeling ventricular enlargement in hydrocephalic brain with finite element method, but this material property for brain tissue has not been investigated in a patient-specific setting in hydrocephalus. Consequently, the accuracy of the simulated ventricular enlargement using this hyperelastic tissue property remains unknown. In this study, we evaluated this brain material model in four patients with communicating hydrocephalus under a small trans-mantle pressure difference (TPMD) between brain ventricle and subarachnoid space (< 1 mmHg). Based upon changes in ventricular geometries obtained with sequential MRI, we found that this hyper-elastic model has a great flexibility and accuracy in modeling ventricular enlargement (with errors less than 1 mm). Our study supports the utility of this hyperelastic constitutive law for future hydrocephalus modeling and suggests that the observed ventricular enlargement in these patients may be caused by a slight increase in TMPD.

A patient-specific, finite element model for noncommunicating hydrocephalus capable of large deformation

A biphasic model for noncommunicating hydrocephalus in patient-specific geometry is proposed. The model can take into account the nonlinear behavior of brain tissue under large deformation, the nonlinear variation of hydraulic conductivity with deformation, and contact with a rigid, impermeable skull using a recently developed algorithm. The model was capable of achieving over a 700 percent ventricular enlargement, which is much greater than in previous studies, primarily due to the use of an anatomically realistic skull recreated from magnetic resonance imaging rather than an artificial skull created by offsetting the outer surface of the cerebrum. The choice of softening or stiffening behavior of brain tissue, both having been demonstrated in previous experimental studies, was found to have a significant effect on the volume and shape of the deformed ventricle, and the consideration of the variation of the hydraulic conductivity with deformation had a modest effect on the deformed ventricle. The model predicts that noncommunicating hydrocephalus occurs for ventricular fluid pressure on the order of 1300 Pa.

The genesis of low pressure hydrocephalus

BACKGROUND

Low pressure hydrocephalus (LPH) is an uncommon entity. Recognition of this treatable condition is important when clinicians are faced with the paradox of symptomatic hydrocephalus despite low intracranial pressures (ICP). Its etiology remains enigmatic.

METHODS

We identified patients with LPH from the prospective, inpatient neuro-intensive care database over a 4-year period (2006-2010).

RESULTS

Nine patients with LPH were identified over a 4-year period. The time from diagnosis of the initial neurosurgical condition to development of LPH varied from 7 days to 5 years. The sub-zero drainage method of Pang and Altschuler was successful in all cases. LPH was accompanied by transependymal edema in five patients despite low ICP. Four patients developed LPH during their initial admission for intracranial bleeding. As patients entered the LPH state, the ICP remained in a normal range yet daily CSF output from the external ventricular drain was reduced. When LPH patients were drained at sub-zero levels, daily CSF output exceeded baseline values for several days and then receded to baseline. Long-term management was achieved with low pressure shunt systems: six programmable shunts; one valveless ventriculoperitoneal shunt; two ventriculopleural shunts. Conditions most commonly associated with LPH are: subarachnoid hemorrhage, chronic hydrocephalus, brain tumors, and chronic CNS infections.

CONCLUSIONS

Low pressure hydrocephalus is a challenging diagnosis. The genesis of LPH was associated with a drop in EVD output, symptomatic ventriculomegaly, and a remarkable absence of intracranial hypertension. When LPH was treated with the sub-zero method, a 'diuresis' of CSF ensued. These observations support a Darcy's flux of brain interstitial fluid due to altered brain poroelastance; in simpler terms, a boggy brain state.

Influences of brain tissue poroelastic constants on intracranial pressure (ICP) during constant-rate infusion

A 3D finite element (FE) model has been developed to study the mean intracranial pressure (ICP) response during constant-rate infusion using linear poroelasticity. Due to the uncertainties in the poroelastic constants for brain tissue, the influence of each of the main parameters on the transient ICP infusion curve was studied. As a prerequisite for transient analysis, steady-state simulations were performed first. The simulated steady-state pressure distribution in the brain tissue for a normal cerebrospinal fluid (CSF) circulation system showed good correlation with experiments from the literature. Furthermore, steady-state ICP closely followed the infusion experiments at different infusion rates. The verified steady-state models then served as a baseline for the subsequent transient models. For transient analysis, the simulated ICP shows a similar tendency to that found in the experiments, however, different values of the poroelastic constants have a significant effect on the infusion curve. The influence of the main poroelastic parameters including the Biot coefficient α, Skempton coefficient B, drained Young's modulus E, Poisson's ratio ν, permeability κ, CSF absorption conductance C(b) and external venous pressure p(b) was studied to investigate the influence on the pressure response. It was found that the value of the specific storage term S(ε) is the dominant factor that influences the infusion curve, and the drained Young's modulus E was identified as the dominant parameter second to S(ε). Based on the simulated infusion curves from the FE model, artificial neural network (ANN) was used to find an optimised parameter set that best fit the experimental curve. The infusion curves from both the FE simulation and using ANN confirmed the limitation of linear poroelasticity in modelling the transient constant-rate infusion.

Is ICP solid or fluid? In vitro biomechanical model using a fluid-saturated gel

Intracranial pressure is mainly considered to be hydrostatic pressure, but observations demonstrated that ICP is heterogeneous within brain suggesting the presence of a solid pressure. Brain tissue is a biphasic material composed of solid and fluid phases. We hypothesized that in a saturated porous model, fluid and solid phases yielded two pressures. Our brain model was 0.5% agar gel. A quasi static compression was applied using a tensile machine. Pressures were gauged within the gel using two different microsensors. One sensor (A) has an open sensitive area measuring the total pressure, whereas the other sensor (B) has a pressure-sensitive area design that gauges mainly the fluid pressure. There was very good agreement between the pressure applied to the gel and the pressure inside the gel measured with sensor A. However, sensor B systematically underestimated the pressure in the gel. We assume that sensor A gauged the total pressure, which is the sum of the pore fluid pressure and mechanical stress, whereas sensor B probably measured only the fluid pressure. The difference between the two sensors reflects the solid part of the total pressure. ICP has to be considered to be the sum of fluid pressure and solid stress.