Altered diffusion and perfusion in hydrocephalic rat brain: a magnetic resonance imaging analysis

Regulation of brain fluid volumes and pressures: basic principles, intracranial hypertension, ventriculomegaly and hydrocephalus

The principles of cerebrospinal fluid (CSF) production, circulation and outflow and regulation of fluid volumes and pressures in the normal brain are summarised. Abnormalities in these aspects in intracranial hypertension, ventriculomegaly and hydrocephalus are discussed. The brain parenchyma has a cellular framework with interstitial fluid (ISF) in the intervening spaces. Framework stress and interstitial fluid pressure (ISFP) combined provide the total stress which, after allowing for gravity, normally equals intracerebral pressure (ICP) with gradients of total stress too small to measure. Fluid pressure may differ from ICP in the parenchyma and collapsed subarachnoid spaces when the parenchyma presses against the meninges. Fluid pressure gradients determine fluid movements. In adults, restricting CSF outflow from subarachnoid spaces produces intracranial hypertension which, when CSF volumes change very little, is called idiopathic intracranial hypertension (iIH). Raised ICP in iIH is accompanied by increased venous sinus pressure, though which is cause and which effect is unclear. In infants with growing skulls, restriction in outflow leads to increased head and CSF volumes. In adults, ventriculomegaly can arise due to cerebral atrophy or, in hydrocephalus, to obstructions to intracranial CSF flow. In non-communicating hydrocephalus, flow through or out of the ventricles is somehow obstructed, whereas in communicating hydrocephalus, the obstruction is somewhere between the cisterna magna and cranial sites of outflow. When normal outflow routes are obstructed, continued CSF production in the ventricles may be partially balanced by outflow through the parenchyma via an oedematous periventricular layer and perivascular spaces. In adults, secondary hydrocephalus with raised ICP results from obvious obstructions to flow. By contrast, with the more subtly obstructed flow seen in normal pressure hydrocephalus (NPH), fluid pressure must be reduced elsewhere, e.g. in some subarachnoid spaces. In idiopathic NPH, where ventriculomegaly is accompanied by gait disturbance, dementia and/or urinary incontinence, the functional deficits can sometimes be reversed by shunting or third ventriculostomy. Parenchymal shrinkage is irreversible in late stage hydrocephalus with cellular framework loss but may not occur in early stages, whether by exclusion of fluid or otherwise. Further studies that are needed to explain the development of hydrocephalus are outlined.

In vivo measurement of T1 and T2 relaxation times in awake pigeon and rat brains at 7T

PURPOSE

Establishment of regional longitudinal (T₁ ) and transverse (T₂ ) relaxation times in awake pigeons and rats at 7T field strength. Regional differences in relaxation times between species and between two different pigeon breeds (homing pigeons and Figurita pigeons) were investigated.

METHODS

T₁ and T₂ relaxation times were determined for nine functionally equivalent brain regions in awake pigeons and rats using a multiple spin-echo saturation recovery method with variable repetition time and a multi-slice/multi-echo sequence, respectively. Optimized head fixation and habituation protocols were applied to accustom animals to the scanning conditions and to minimize movement.

RESULTS

The habituation protocol successfully limited movement of the awake animals to a negligible minimum, allowing reliable measurement of T₁ and T₂ values within all regions of interest. Significant differences in relaxation times were found between rats and pigeons but not between different pigeon breeds.

CONCLUSION

The obtained T₁ and T₂ values for awake pigeons and rats and the optimized habituation protocol will augment future MRI studies with awake animals. The differences in relaxation times observed between species underline the importance of the acquisition of T₁ /T₂ values as reference points for specific experiments. Magn Reson Med 79:1090-1100, 2018. © 2017 International Society for Magnetic Resonance in Medicine.

Changes of fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in the model of experimental acute hydrocephalus in rabbits

BACKGROUND

To study the integrity of white matter, we investigated the correlation between the changes in neuroradiological and morphological parameters in an animal model of acute obstructive hydrocephalus.

METHODS

Hydrocephalus was induced in New Zealand rabbits (n = 10) by stereotactic injection of kaolin into the lateral ventricles. Control animals received saline in place of kaolin (n = 10). The progression of hydrocephalus was assessed using magnetic resonance imaging. Regional fractional anisotropy (FA) and the apparent diffusion coefficient (ADC) were measured in several white matter regions before and after the infusion of kaolin. Morphology of myelinated nerve fibers as well as of the blood-brain barrier were studied with the help of transmission electron microscopy (TEM) and light microscopy.

RESULTS

Compared with control animals, kaolin injection into the ventricles resulted in a dramatic increase in ventricular volume with compression of basal cisterns, brain shift and periventricular edema (as observed on magnetic resonance imaging [MRI]). The values of ADC in the periventricular and periaqueductal areas significantly increased in the experimental group (P < 0.05). FA decreased by a factor of 2 in the zones of periventricular, periaqueductal white matter and corpus collosum. Histological analysis demonstrated the impairment of the white matter and necrobiotic changes in the cortex. Microsctructural alterations of the myelin fibers were further proved with the help of TEM. Blood-brain barrier ultrastructure assessment showed the loss of its integrity.

CONCLUSIONS

The study demonstrated the correlation of the neuroradiological parameters with morphological changes. The abnormality of the FA and ADC parameters in the obstructive hydrocephalus represents a significant implication for the diagnostics and management of hydrocephalus in patients.

Cerebrospinal fluid absorption block at the vertex in chronic hydrocephalus: obstructed arachnoid granulations or elevated venous pressure?

Background

The lack of absorption of CSF at the vertex in chronic hydrocephalus has been ascribed to an elevation in the arachnoid granulation outflow resistance (R_out). The CSF infusion studies measuring R_out are dependent on venous sinus pressure but little is known about the changes in pressure which occur throughout life or with the development of hydrocephalus.

Methods

Twenty patients with chronic hydrocephalus underwent MR venography and MR flow quantification techniques. The venous outflow pressure was estimated from the sinus blood flow and the cross-sectional area of the transverse sinuses. Adult controls as well as a normal young cohort were selected to estimate the change in sinus pressure which occurs throughout life and following the development of hydrocephalus. Significance was tested with a Student’s t-test.

Results

The size of the transverse sinuses was unchanged from the 1^st to the 5^th decade of life, indicating a stable outflow resistance. However, the blood flow was reduced by 42%, indicating a likely similar reduction in pressure gradient across the sinuses. The sinuses of hydrocephalus patients were 38% smaller than matched controls, indicating a 2.5 times increase in resistance. Despite the 24% reduction in blood flow, a significant increase in sinus pressure is suggested.

Conclusions

The size of the venous sinuses normally does not change over the age range investigated but sinus pressure is reduced proportional to an age-related blood flow reduction. Hydrocephalus is associated with much smaller sinuses than normal and an elevation in venous pressure may explain the lack of CSF absorption into the arachnoid granulations in chronic hydrocephalus.

Diffusion-weighted imaging of the cerebellum in the fetus with Chiari II malformation

BACKGROUND AND PURPOSE

Diffusion-weighted imaging can be used to characterize brain maturation. MR imaging of the fetus is used in cases of suspected Chiari II malformation when further evaluation of the posterior fossa is required. We sought to investigate whether there were any quantitative ADC abnormalities of the cerebellum in fetuses with this malformation.

MATERIALS AND METHODS

Measurements from ROIs acquired in each cerebellar hemisphere and the pons were obtained from calculated ADC maps performed on our Avanto 1.5T imaging system. Values in groups of patients with Chiari II malformations were compared with those from fetuses with structurally normal brains, allowing for the dependent variable of GA by using linear regression analysis.

RESULTS

There were 8 fetuses with Chiari II malformations and 23 healthy fetuses, ranging from 20 to 31 GW. There was a significant linear decline in the cerebellar ADC values with advancing gestation in our healthy fetus group, as expected. The ADC values of the cerebellum of fetuses with Chiari II malformation were higher [1820 (±100) × 10⁻⁶ mm²/s] than ADC values in the healthy fetuses (1370 ± 70) × 10⁻⁶ mm²/s. This was statistically significant, even when allowing for the dependent variable of GA (P = .0126). There was no significant difference between the pons ADC values in these groups (P = .645).

CONCLUSIONS

While abnormal white matter organization or early cerebellar degeneration could potentially contribute to our findings, the most plausible explanation pertains to abnormalities of CSF drainage in the posterior fossa, with increased extracellular water possibly accounting for this phenomenon.

Intraventricular hemorrhage induces deposition of proteoglycans in premature rabbits, but their in vivo degradation with chondroitinase does not restore myelination, ventricle size and neurological recovery

Intraventricular hemorrhage (IVH) results in white matter injury and hydrocephalus in premature infants. Chondroitin sulfate proteoglycans (CSPGs)-neuorcan, brevican, versican, aggrecan and phosphacan-are unregulated in the extracellular matrix after brain injury, and their degradation enhances plasticity of the brain. Therefore, we hypothesized that CSPG levels were elevated in the forebrain of premature infants with IVH and that in vivo degradation of CSPGs would enhance maturation of oligodendrocyte, augment myelination, promote neurological recovery, and minimize hydrocephalus. We found that levels of neurocan, brevican, aggrecan, phosphacan, and versican were elevated, whereas NG2 expression was reduced in premature rabbit pups and human infants with IVH compared to controls. Intracerebroventricular chondroitinase ABC (ChABC) reduced the expression of neuorcan, brevican, versican and aggrecan, but not NG2. However, ChABC treatment did not enhance maturation of oligodendrocytes, myelination, or neurological recovery in the pups with IVH. Moreover, ChABC did not reduce gliosis or ventriculomegaly. Our results demonstrate that IVH induces distinct changes in the components of CSPGs, and that reversing these changes by in vivo ChABC treatment neither promotes clinical recovery, myelination, nor reduces ventriculomegaly in preterm rabbit pups.

Magnetic resonance imaging indicators of blood-brain barrier and brain water changes in young rats with kaolin-induced hydrocephalus

BACKGROUND

Hydrocephalus is associated with enlargement of cerebral ventricles. We hypothesized that magnetic resonance (MR) imaging parameters known to be influenced by tissue water content would change in parallel with ventricle size in young rats and that changes in blood-brain barrier (BBB) permeability would be detected.

METHODS

Hydrocephalus was induced by injection of kaolin into the cisterna magna of 4-week-old rats, which were studied 1 or 3 weeks later. MR was used to measure longitudinal and transverse relaxation times (T1 and T2) and apparent diffusion coefficients in several regions. Brain tissue water content was measured by the wet-dry weight method, and tissue density was measured in Percoll gradient columns. BBB permeability was measured by quantitative imaging of changes on T1-weighted images following injection of gadolinium diethylenetriamine penta-acetate (Gd-DTPA) tracer and microscopically by detection of fluorescent dextran conjugates.

RESULTS

In nonhydrocephalic rats, water content decreased progressively from age 3 to 7 weeks. T1 and T2 and apparent diffusion coefficients did not exhibit parallel changes and there was no evidence of BBB permeability to tracers. The cerebral ventricles enlarged progressively in the weeks following kaolin injection. In hydrocephalic rats, the dorsal cortex was more dense and the white matter less so, indicating that the increased water content was largely confined to white matter. Hydrocephalus was associated with transient elevation of T1 in gray and white matter and persistent elevation of T2 in white matter. Changes in the apparent diffusion coefficients were significant only in white matter. Ventricle size correlated significantly with dorsal water content, T1, T2, and apparent diffusion coefficients. MR imaging showed evidence of Gd-DTPA leakage in periventricular tissue foci but not diffusely. These correlated with microscopic leak of larger dextran tracers.

CONCLUSIONS

MR characteristics cannot be used as direct surrogates for water content in the immature rat model of hydrocephalus, probably because they are also influenced by other changes in tissue composition that occur during brain maturation. There is no evidence for widespread persistent opening of BBB as a consequence of hydrocephalus in young rats. However, increase in focal BBB permeability suggests that periventricular blood vessels may be disrupted.

Negative-pressure and low-pressure hydrocephalus: the role of cerebrospinal fluid leaks resulting from surgical approaches to the cranial base

OBJECT

Negative-pressure and low-pressure hydrocephalus are rare clinical entities that are frequently misdiagnosed. They are characterized by recurrent episodes of shunt failure because the intracranial pressure is lower than the opening pressure of the valve. In this report the authors discuss iatrogenic CSF leaks as a cause of low- or negative-pressure hydrocephalus after approaches to the cranial base.

METHODS

The authors retrospectively reviewed cases of low-pressure or negative-pressure hydrocephalus presenting after cranial approaches complicated with a CSF leak at their institution.

RESULTS

Three patients were identified. Symptoms of high intracranial pressure and ventriculomegaly were present, although the measured pressures were low or negative. A blocked communication between the ventricles and the subarachnoid space was documented in 2 of the cases and presumed in the third. Shunt revisions failed repeatedly. In all cases, temporary clinical and radiographic improvement resulted from external ventricular drainage at subatmospheric pressures. The CSF leaks were sealed and CSF communication was reestablished operatively. In 1 case, neck wrapping was used with temporary success.

CONCLUSIONS

Negative-pressure or low-pressure hydrocephalus associated with CSF leaks, especially after cranial base approaches, is difficult to treat. The solution often requires the utilization of subatmospheric external ventricular drains to establish a lower ventricular drainage pressure than the drainage pressure created in the subarachnoid space, where the pressure is artificially lowered by the CSF leak. Treatment involves correction of the CSF leak, neck wrapping to increase brain turgor and allow the pressure in the ventricles to rise to the level of the opening pressure of the valve, and reestablishing the CSF route.

Hydrocephalus induces dynamic spatiotemporal regulation of aquaporin-4 expression in the rat brain

BACKGROUND

The water channel protein aquaporin-4 (AQP4) is reported to be of possible major importance for accessory cerebrospinal fluid (CSF) circulation pathways. We hypothesized that changes in AQP4 expression in specific brain regions correspond to the severity and duration of hydrocephalus.

METHODS

Hydrocephalus was induced in adult rats (~8 weeks) by intracisternal kaolin injection and evaluated after two days, one week and two weeks. Using magnetic resonance imaging (MRI) we quantified lateral ventricular volume, water diffusion and blood-brain barrier properties in hydrocephalic and control animals. The brains were analysed for AQP4 density by western blotting and localisation by immunohistochemistry. Double fluorescence labelling was used to study cell specific origin of AQP4.

RESULTS

Lateral ventricular volume was significantly increased over control at all time points after induction and the periventricular apparent diffusion coefficient (ADC) value significantly increased after one and two weeks of hydrocephalus. Relative AQP4 density was significantly decreased in both cortex and periventricular region after two days and normalized after one week. After two weeks, periventricular AQP4 expression was significantly increased. Relative periventricular AQP4 density was significantly correlated to lateral ventricular volume. AQP4 immunohistochemical analysis demonstrated the morphological expression pattern of AQP4 in hydrocephalus in astrocytes and ventricular ependyma. AQP4 co-localized with astrocytic glial fibrillary acidic protein (GFAP) in glia limitans. In vascular structures, AQP4 co-localized to astroglia but not to microglia or endothelial cells.

CONCLUSIONS

AQP4 levels are significantly altered in a time and region dependent manner in kaolin-induced hydrocephalus. The presented data suggest that AQP4 could play an important neurodefensive role, and may be a promising future pharmaceutical target in hydrocephalus and CSF disorders.

Longitudinal diffusion-weighted imaging in infants with hydrocephalus: decrease in tissue water diffusion after cerebrospinal fluid diversion

OBJECT

Progressive hydrocephalus may lead to edema of the periventricular white matter and to damage of the brain parenchyma because of compression, stretching, and ischemia. The aim of the present study was to investigate whether cerebral edema can be quantified using diffusion-weighted imaging in infants with hydrocephalus and whether CSF diversion could decrease cerebral edema.

METHODS

Diffusion-weighted MR imaging was performed in 24 infants with progressive hydrocephalus before and after CSF diversion. Parametric images of the trace apparent diffusion coefficients (ADCs) were obtained. The ADCs of 5 different cortical and subcortical regions of interest were calculated pre- and postoperatively in each patient. The ADC values were compared with age-related normal values. Mean arterial blood pressure and anterior fontanel pressure were measured immediately after each MR imaging study.

RESULTS

After CSF diversion, the mean ADC decreased from a preoperative value of 1209 +/- 116 x 10(-6) mm(2)/second to a postoperative value of 928 +/- 64 x 10(-6) mm(2)/second (p < 0.005). Differences between pre- and postoperative ADC values were most prominent in the periventricular white matter, supporting the existence of preoperative periventricular edema. Compared with age-related normal values, the preoperative ADC values were higher and the postoperative ADC values were lower, although within normal range. The decrease in ADC after CSF drainage was more rapid than the more gradual physiological decrease that is related to age. The preoperative ICP was elevated in all patients. After CSF diversion the ICP decreased significantly to within the normal range. A linear correlation between ADC values and ICP was found (correlation coefficient 0.496, p < 0.001). In all patients the mean arterial blood pressure was within physiological limits both pre- and postoperatively.

CONCLUSIONS

This study shows a rapid and more extensive decrease in ADC values after CSF diversion than is to be expected from physiological ADC decrease solely due to increasing patient age. The preoperative ADC increase can be explained by interstitial edema caused by transependymal CSF leakage or by vasogenic edema caused by capillary compression and stretching of the brain parenchyma. This study population of infants with (early recognized) hydrocephalus did not suffer from cytotoxic edema. These findings may help to detect patients at risk for cerebral damage by differentiating between progressive and compensated hydrocephalus.

Gray matter metabolism in acute and chronic hydrocephalus

Although hydrocephalus is usually considered a disorder of periventricular white matter, disturbance of gray matter is probably also involved. However, so far gray matter metabolism has not been studied in experimental hydrocephalus using high resolution in vivo magnetic resonance spectroscopy (MRS). Therefore 15 rats were made hydrocephalic by injection of 0.1 ml kaolin into the cisterna magna, whereas 10 sham-operated rats served as controls. (1)H MRS and magnetic resonance imaging were performed longitudinally in acute hydrocephalus 2 and 4 weeks after kaolin treatment and in chronic hydrocephalus after 6 weeks. Volumes of interest included the gray matter regions cortex, thalamus and hippocampus. In hydrocephalic animals, (1)H MRS revealed decreased glutamate levels in all examined areas at all time points. Moreover, in acute hydrocephalus disturbances were noted in the hippocampus with decreased concentrations of N-acetyl aspartate, creatine, inositol and taurine, and in the cortex with decreased taurine levels. A clear lactate peak was detected in CSF spectra from hydrocephalic rats. In addition, T2-weighted images showed increase of free water in the hippocampus. It can be concluded that glutamate metabolism is deranged in gray matter in acute and chronic hydrocephalus in rats. If confirmed in humans, early detection of glutamatergic disturbances and lactate accumulation using in vivo(1)H MRS might serve as an indication for surgical treatment of hydrocephalus before irreversible neuronal damage develops.

White matter microstructural abnormalities in children with spina bifida myelomeningocele and hydrocephalus: a diffusion tensor tractography study of the association pathways

PURPOSE

To quantify microstructural abnormalities in the major association pathways of children affected by spina bifida myelomeningocele (SBM) and shunted hydrocephalus using whole-brain diffusion tensor imaging (DTI).

MATERIALS AND METHODS

The institutional review board approved this Health Insurance Portability and Accountability Act (HIPAA)-compliant study and written informed consent/assent were obtained prior to the study. The 69 participants included 38 children with SBM and shunted hydrocephalus (age mean +/- SD = 12.30 +/- 2.10 years; 22 boys; 10 left-handed) and 31 age- and sex-matched normally-developing children (11.56 +/- 2.72 years; 15 boys, four left-handed). Diffusion tensor tractography (DTT) was performed to delineate and quantify bilaterally four major association pathways (arcuate, inferior longitudinal, inferior fronto-occipital, and uncinate fasciculi).

RESULTS

The group with SBM did not exhibit the pattern of age-related decreases in the diffusivities observed in the controls. The transverse and axial diffusivities were significantly elevated in most of the white matter pathways of the participants with SBM. The fractional anisotropy (FA) was significantly lower in most of the association pathways. Many of the association pathways were not traceable in some participants with SBM compared to the controls at the selected FA thresholds.

CONCLUSION

DTT revealed diffusion tensor characteristics of abnormal development (nonvisualization/poor visualization of tracts, downward arrow FA, upward arrow diffusivities), impairment in myelination (upward arrow transverse diffusivity) as well as abnormalities in intrinsic axonal characteristics and extraaxonal/extracellular space (upward arrow axial diffusivity) in the association pathways of the SBM children. The differences in the diffusion metrics observed in the children with SBM are suggestive of abnormal white matter development and persistent degeneration with increased age.

Effect of hydrocephalus on rat brain extracellular compartment

Background

The cerebral cortex may be compressed in hydrocephalus and some experiments suggest that movement of extracellular substances through the cortex is impaired. We hypothesized that the extracellular compartment is reduced in size and that the composition of the extracellular compartment changes in rat brains with kaolin-induced hydrocephalus.

Methods

We studied neonatal (newborn) onset hydrocephalus for 1 or 3 weeks, juvenile (3 weeks) onset hydrocephalus for 3–4 weeks or 9 months, and young adult (10 weeks) onset hydrocephalus for 2 weeks, after kaolin injection. Freeze substitution electron microscopy was used to measure the size of the extracellular compartment. Western blotting and immunohistochemistry with quantitative image densitometry was used to study the extracellular matrix constituents, phosphacan, neurocan, NG2, decorin, biglycan, and laminin.

Results

The extracellular space in cortical layer 1 was reduced significantly from 16.5 to 9.6% in adult rats with 2 weeks duration hydrocephalus. Western blot and immunohistochemistry showed that neurocan increased only in the periventricular white matter following neonatal induction and 3 weeks duration hydrocephalus. The same rats showed mild decorin increases in white matter and around cortical neurons. Juvenile and adult onset hydrocephalus was associated with no significant changes.

Conclusion

We conclude that compositional changes in the extracellular compartment are negligible in cerebral cortex of hydrocephalic rats at various ages. Therefore, the functional change related to extracellular fluid flow should be reversible.

Apparent diffusion coefficient and cerebrospinal fluid flow measurements in patients with hydrocephalus

OBJECTIVE

To evaluate the efficacy of diffusion magnetic resonance imaging and compare with cerebrospinal fluid (CSF) flow imaging in patients with hydrocephalus before and after treatment.

METHODS

Twenty patients with hydrocephalus (group 1, pediatric, with primary aqueductal stenosis, n = 10; group 2, adult, with normal-pressure hydrocephalus, n = 10) and 20 age-matched healthy subjects that served as controls were examined. Cerebrospinal fluid flow velocity interval was calculated as the mean absolute values of the peak craniocaudal velocity and caudocranial velocity on CSF flow measurements. On diffusion magnetic resonance imaging, apparent diffusion coefficient (ADC) values from 8 regions were evaluated.

RESULTS

The decrease in ADC values after treatment was significant in both groups (P < 0.001 for both). Preoperative mean CSF flow velocity interval value was significantly lower in group 1 and significantly higher than postoperative and control group values in group 2 (P < 0.001 for all).

CONCLUSION

The ADC values increase in hydrocephalus and decrease significantly after treatment. Preoperative ADC value may serve as baseline, and the change in ADC may be an indicator of response to treatment and CSF flow measurements.

Brain metabolism in adult chronic hydrocephalus

Normal pressure hydrocephalus (NPH) is the most frequent form of chronic hydrocephalus in adults. NPH remains underdiagnosed although between 5% and 10% of all demented patients may suffer from this disorder. As dementia is an increasing demographic problem, treatable forms such as in NPH have become a central issue in neurology. Despite the traditional perception of hydrocephalus being a disorder of disturbed CSF dynamics, in NPH metabolic impairment seems at least as important. So far, the only valid animal model of NPH is chronic adult kaolin hydrocephalus. In this model, opening of alternative CSF outflow pathways leads to normal or near-normal intracranial pressure and CSF outflow resistance. Yet, various metabolic disturbances cause ongoing ventricular enlargement and characteristic symptoms including cognitive decline and gait ataxia. Delayed hippocampal neuronal death, accumulation of beta-amyloid and disturbed cholinergic neurotransmission may contribute to memory dysfunction. Compromised periventricular blood flow, decreased dopamine levels in the substantia nigra and damaged striatal GABAergic interneurons may reflect basal ganglia symptoms. At least in human hydrocephalus cerebrovascular co-morbidity of the white matter plays an important role as well. It seems that in hydrocephalus from a certain 'point of no return' metabolic impairment becomes decoupled from CSF dynamics and, at least partly, self-sustained. This is probably the reason why despite restored CSF circulation by shunting many patients with chronic hydrocephalus still suffer from severe neurological deficits. The present paper offers a comprehensive review of the experimental and clinical data suggesting metabolic disturbances in chronic hydrocephalus.

In vivo study of experimental pneumococcal meningitis using magnetic resonance imaging

BACKGROUND

Magnetic Resonance Imaging (MRI) methods were evaluated as a tool for the study of experimental meningitis. The identification and characterisation of pathophysiological parameters that vary during the course of the disease could be used as markers for future studies of new treatment strategies.

METHODS

Rats infected intracisternally with S. pneumoniae (n = 29) or saline (n = 13) were randomized for imaging at 6, 12, 24, 30, 36, 42 or 48 hours after infection. T1W, T2W, quantitative diffusion, and post contrast T1W images were acquired at 4.7 T. Dynamic MRI (dMRI) was used to evaluate blood-brain-barrier (BBB) permeability and to obtain a measure of cerebral and muscle perfusion. Clinical- and motor scores, bacterial counts in CSF and blood, and WBC counts in CSF were measured.

RESULTS

MR images and dMRI revealed the development of a highly significant increase in BBB permeability (P < 0.002) and ventricle size (P < 0.0001) among infected rats. Clinical disease severity was closely related to ventricle expansion (P = 0.024). Changes in brain water distribution, assessed by ADC, and categorization of brain 'perfusion' by cortex DeltaSI(bolus) were subject to increased inter-rat variation as the disease progressed, but without overall differences compared to uninfected rats (P > 0.05). Areas of well-'perfused' muscle decreased with the progression of infection indicative of septicaemia (P = 0.05).

CONCLUSION

The evolution of bacterial meningitis was successfully followed in-vivo with MRI. Increasing BBB-breakdown and ventricle size was observed in rats with meningitis whereas changes in brain water distribution were heterogeneous. MRI will be a valuable technique for future studies aiming at evaluating or optimizing adjunctive treatments.

T1 relaxation in in vivo mouse brain at ultra-high field

Accurate knowledge of relaxation times is imperative for adjustment of MRI parameters to obtain optimal signal-to-noise ratio (SNR) and contrast. As small animal MRI studies are extended to increasingly higher magnetic fields, these parameters must be assessed anew. The goal of this study was to obtain accurate spin-lattice (T(1)) relaxation times for the normal mouse brain at field strengths of 9.4 and 17.6 T. T(1) relaxation times were determined for cortex, corpus callosum, caudate putamen, hippocampus, periaqueductal gray, lateral ventricle, and cerebellum and varied from 1651 +/- 28 to 2449 +/- 150 ms at 9.4 T and 1824 +/- 101 to 2772 +/- 235 ms at 17.6 T. A field strength-dependent increase of T(1) relaxation times is shown. The SNR increase at 17.6 T is in good agreement with the expected SNR increase for a sample-dominated noise regime.

Aquaporin 4 changes in rat brain with severe hydrocephalus

Hydrocephalus is characterized by impaired cerebrospinal fluid (CSF) flow with enlargement of the ventricular cavities of the brain and progressive damage to surrounding tissue. Bulk water movement is altered in these brains. We hypothesized that increased expression of aquaporins, which are water-permeable channel proteins, would occur in these brains to facilitate water shifts. We used quantitative (real-time) RT-PCR, Western blotting and immunohistochemistry to evaluate the brain expression of aquaporins (AQP) 1, 4, and 9 mRNA and protein in Sprague-Dawley rats rendered hydrocephalic by injection of kaolin into cistern magna. AQP4 mRNA was significantly up-regulated in parietal cerebrum and hippocampus 4 weeks and 9 months after induction of hydrocephalus (P < 0.05). Although Western blot analysis showed no significant change, there was more intense perivascular AQP4 immunoreactivity in cerebrum of hydrocephalic brains at 3-4 weeks after induction. We did not detect mRNA or protein changes in AQP1 (located in choroid plexus) or AQP9 (located in select neuron populations). Kir4.1, a potassium channel protein linked to water flux, exhibited enhanced immunoreactivity in the cerebral cortex of hydrocephalic rats; the perineuronal distribution was entirely different from that of AQP4. These results suggest that brain AQP4 up-regulation might be a compensatory response to maintain water homeostasis in hydrocephalus.

Cellular damage and prevention in childhood hydrocephalus

The literature concerning brain damage due to hydrocephalus, especially in children and animal models, is reviewed. The following conclusions are reached: 1. Hydrocephalus has a deleterious effect on brain that is dependent on magnitude and duration of ventriculomegaly and modified by the age of onset. 2. Animal models have many histopathological similarities to humans and can be used to understand the pathogenesis of brain damage. 3. Periventricular axons and myelin are the primary targets of injury. The pathogenesis has similarities to traumatic and ischemic white matter injury. Secondary changes in neurons reflect compensation to the stress or ultimately the disconnection. 4. Altered efflux of extracellular fluid could result in accumulation of waste products that might interfere with neuron function. Further research is needed in this as well as the blood-brain barrier in hydrocephalus. 5. Some, but not all, of the changes are preventable by shunting CSF. However, axon loss cannot be reversed, therefore shunting in a given case must be considered carefully. 6. Experimental work has so far failed to show any benefit in reducing CSF production. Pharmacologic protection of the brain, at least as a temporary measure, holds some promise but more pre-clinical research is required.

Imaging of murine brain tumors using a 1.5 Tesla clinical MRI system

BACKGROUND

In this study, we investigated the feasibility of using a 1.5 Tesla (T) clinical magnetic resonance imaging (MRI) system for in vivo assessment of three histopathologically different brain tumor models in mice.

METHODS

We selected mouse models in which tumor growth was observed in different intracranial compartments: Patched+/- heterozygous knock-out mice for tumor growth in the cerebellum (n = 5); U87 MG human astrocytoma cells xenografted to the frontal lobe of athymic mice (n = 15); and F5 (n = 15) or IOMM Lee (n = 15) human malignant meningioma cells xenotransplanted to the athymic mouse skull base or convexity. Mice were imaged using a small receiver surface coil and a clinical 1.5 T MRI system. T1- and fast spin echo T2-weighted image sequences were obtained in all animals. Gadolinium was injected via tail vein to better delineate the intracranial tumors. Twenty mice were followed by serial MRI to study tumor growth over time. In these mice, images were typically performed after tumor implantation, and at two week intervals. Mice were euthanized following their last imaging procedure, and their tumors were examined by histopathology. The histopathological preparations were then compared to the last MR images to correlate the imaging features with the pathology.

RESULTS

Magnetic resonance imaging delineated th tumors in the cerebellum, frontal lobes and skull base in all mouse models. The detection of intracranial tumors was enhanced with prio administration of gadolinium, and the limit of resolution of brain tumors in the mice was 1-2 mm3. Sequential images performed at different time intervals showed progressive tumor growth in all animals. The MR images of tumor size and location correlated accurately with th results of the histopathological analysis.

CONCLUSION

Magnetic resonance imaging of murine brain tumors in different intracrania compartments is feasible with a 1.5 T clinical MR system and a specially designed surface coil. Tumors as small as 1-2 mm3 can be detecte with good image resolution. Mice harbouring nascent brain tumors can be followed sequentially by serial MR imaging. This may allow for a noninvasive means by which tumor growth can be measured, and novel therapies tested without resorting to sacrifice of the mice.

In utero surgery for hydrocephalus

INTRODUCTION

Neonatal hydrocephalus is one of the most common congenital anomalies affecting the nervous system.

DISCUSSION

Currently, ultrasonography allows for early detection of fetal ventriculomegaly and presents the family with several treatment options: termination of pregnancy, early delivery and neonatal shunting, and delivery at term followed by shunting. Despite ventricular decompression after birth, the cognitive outcome is variable as prolonged in utero hydrocephalus has a detrimental effect. In the early 1980s, fetal intervention was explored with the intention of improving outcome. However, patient selection was poor. Fetal ventriculomegaly from other conditions was not adequately distinguished from fetal hydrocephalus. In addition, fetal surgical techniques were not advanced. Consequently, the results were poor and a de facto moratorium on fetal shunting was imposed. However, recent improvements in fetal imaging, such as magnetic resonance imaging, and advances in fetal surgical techniques offer the possibility that properly selected fetuses with hydrocephalus can benefit from an in utero intervention.

Magnesium sulfate therapy is of mild benefit to young rats with kaolin-induced hydrocephalus

Hydrocephalus causes damage to periventricular white matter at least in part through chronic ischemia. Magnesium sulfate (MgSO4) has been shown to be protective in various models of neurologic injury. We hypothesized that this agent would ameliorate the effects of experimental childhood-onset hydrocephalus. Hydrocephalus was induced in 3- and 4-wk-old rats by injection of kaolin into the cisterna magna. Tests of cognitive and motor function were performed on a weekly basis. In a blinded and randomized manner, MgSO4 was administered in two separate experiments (s.c. injection 0.85, 4.1, or 8.2 mM/kg/d), supplemented by osmotic minipump infusion (0.03 mM/d) to prevent low trough levels for 2 wk, beginning 2 wk after induction of hydrocephalus. The brains were then subjected to histopathological and biochemical analyses. With the 4.1 mM/kg/d dose, serum Mg++ levels were elevated transiently from 1.3 to approximately 7 mM/L. We observed statistically significant improvement in gait performance and reduced astroglial reaction. There was also a trend to improved memory performance, but no evidence of increased myelin or synaptic protein content. The 8.2 mM/kg/d dose was associated with sedation and there was no evidence of improvement in any parameter. We conclude that MgSO4 might be mildly protective in experimental hydrocephalus.

Study of corpus callosum in experimental hydrocephalic wistar rats

PURPOSE: Hydrocephalus causes countless cerebral damages, especially on the structures around the ventricles. Hydrocephalic children present deficiencies in the nonverbal skills more than in the verbal skills, and not always revertible with an early treatment. As the corpus callosum has an important role in the nonverbal acquisition it is possible that the injuries in this structure are responsible for the cognitive dysfunctions of these children. This present study tries to establish the alterations caused by hydrocephalus on the corpus callosum of developing Wistar rats, induced by intracisternal injection of kaolin. METHODS : Seven, fourteen and twenty one days after the injection, the animals were killed, and the corpus callosum was dissected and prepared for the study of the axonal fibers. RESULTS AND CONCLUSION: The seven-day old rats in hydrocephalus development presented a delay in myelination in relation to the control rats. With the fourteen-day old rats in hydrocephalus development the corpus callosum showed a recovery of myelin, but with the twenty one-day old rats in hydrocephalus development the axonal fibers were damaged and reduced in number.

Advances in postnatal neuroimaging: relevance to pathogenesis and treatment of brain injury

The human brain is susceptible to a wide variety of insults. The permanent residua of these abnormalities are represented in dysfunction of one or more areas of neurodevelopment. A full understanding of normal brain development, mechanisms of brain injury, and consequences for subsequent brain development is required to determine which infants are at risk for neurodevelopmental handicap, and to monitor the effects of new treatments and management regimens designed to prevent these disabilities. Advanced magnetic resonance techniques, such as quantitative morphometric magnetic resonance techniques, diffusion-weighted magnetic resonance techniques, and magnetic resonance spectroscopy applied to the study of early human brain development have given us a better understanding of the pathophysiologic mechanisms of brain injury and its effects on subsequent brain development. Magnetic resonance imaging has provided an invaluable tool for the study of the fetal and newborn brain in vivo.

Analysis of age-dependant alteration in the brain gene expression profile following induction of hydrocephalus in rats

Hydrocephalus is associated with gradual progressive impairment and destruction of cerebral axons and neurons. To provide a comprehensive analysis of gene expression changes in brain due to experimental hydrocephalus we used a DNA microarray screening technique. Hydrocephalus was induced in 3-week-old and 8- to 10-week-old rats by injection of kaolin into cisterna magna. Following induction of hydrocephalus, samples of frontoparietal cerebrum were studied 3 and 36 weeks later in young rats and 1.5 weeks later in adult rats. At the transcriptional level, young rats with subacute hydrocephalus showed overexpression of genes involved in synaptic transmission in parallel to genes associated with protective and compensatory mechanisms. Those with chronic hydrocephalus exhibited some similar changes among synapse-related genes but suppression of other neuronal genes. Expression of myelin-related genes was increased in both groups of rats with early onset hydrocephalus but suppressed in adult rats with acute hydrocephalus. Changes in genes related to extracellular matrix molecules suggest that there might be remodeling in this compartment. Adult rats showed elevated expression of inflammatory genes, likely related to kaolin-induced inflammation, but they failed to show changes in genes involved in compensatory or protective mechanisms. These results indicate that there is an age- and duration-dependent difference in the gene expression profiles of kaolin-induced hydrocephalus and they present avenues for future research.

Protective effect of nimodipine on behavior and white matter of rats with hydrocephalus

OBJECT

Hydrocephalus, a pathological dilation of the ventricles of the brain, causes damage to periventricular white matter, at least in part, through chronic ischemia. The authors tested the hypothesis that treatment with nimodipine, an L-type calcium channel-blocking agent with demonstrated efficacy in a range of cerebral ischemic disorders, would ameliorate the adverse effects of experimental hydrocephalus.

METHODS

Hydrocephalus was induced in 3-week-old rats by injection of kaolin into the cisterna magna. The rats were treated by continuous administration of nimodipine or control vehicle for 2 weeks, beginning 2 weeks after induction of hydrocephalus. During the treatment period, the animals underwent repeated tests of motor and cognitive behavior. At the end of the treatment period, the rat brains were analyzed by histopathological and biochemical means. Nimodipine treatment prevented the declines in motor and cognitive behavior that were observed in untreated control rats. During the treatment period, ventricular enlargement, determined by magnetic resonance imaging, was equal in the two groups, although the corpus callosum was thicker in the treated rats. Myelin content in white matter and synaptophysin content in gray matter, an indicator of synapses, did not differ.

CONCLUSIONS

The protective effect of nimodipine is most likely based on improved blood flow, although prevention of calcium influx-mediated proteolytic processes in axons cannot be excluded. Adjunctive pharmacological therapy may be beneficial to patients with hydrocephalus.

Calcium-mediated proteolytic damage in white matter of hydrocephalic rats?

Hydrocephalus is a pathological dilatation of the cerebrospinal fluid (CSF)-containing ventricles of the brain. Damage to periventricular white matter is multifactorial with contributions by chronic ischemia and gradual physical distortion. Acute ischemic and traumatic brain injuries are associated with calcium-dependent activation of proteolytic enzymes. We hypothesized that hydrocephalus is associated with calcium ion accumulation and proteolytic enzyme activation in cerebral white matter. Hydrocephalus was induced in immature and adult rats by injection of kaolin into the cisterna magna and several different experimental approaches were used. Using the glyoxal bis (2-hydroxyanil) method, free calcium ion was detected in periventricular white matter at sites of histological injury. Western blot determinations showed accumulation of calpain I (mu-calpain) and immunoreactivity for calpain I was increased in periventricular axons of young hydrocephalic rats. Proteolytic cleavage of a fluorogenic calpain substrate was demonstrated in white matter. Immunoreactivity for spectrin breakdown products was detected in scattered callosal axons of young hydrocephalic rats. The findings support the hypothesis that periventricular white matter damage associated with experimental hydrocephalus is due, at least in part, to calcium-activated proteolytic processes. This may have implications for supplemental drug treatments of this disorder.