Background: Symptomatic or active hydrocephalus in children is linked to an elevation in intracranial pressure (ICP), which is likely to be multifactorial in origin. The CSF outflow resistance, venous sinus resistance and total cerebral blood flow are likely factors in the ICP elevation. The purpose of this paper is to define the incidence, site and significance of venous sinus stenosis and/or cerebral hyperemia in a cohort of children diagnosed with hydrocephalus at a tertiary referral hospital. Methods: The imaging database was reviewed over a 10 year period and the index MRI of all children between the ages of 4 months and 15 years, who were diagnosed with treatment naive hydrocephalus of any type (excluding secondary to tumor) and had magnetic resonance venography (MRV) and flow quantification were selected. Patients were compared with children undergoing an MRI with MRV and flow quantification who were subsequently shown to have no abnormality. The cross-sectional area and circumference of the sinuses were measured at 4 levels. The hydraulic and effective diameters were calculated. An area stenosis of 65% or greater was deemed significant. A total cerebral blood flow greater than two standard deviations above the mean for controls was taken to be abnormal. Results: There were a total of 55 children with hydrocephalus compared to 118 age matched control MRV's and 35 control flow quantification studies. A high grade stenosis occurred in 56% of patients but in none of the controls (p < 0.0001). The commonest site of narrowing was in the distal sigmoid sinus. Cerebral hyperemia occurred in 13% of patients but did not occur in the controls. Conclusions: The elevation in ICP in symptomatic hydrocephalus is multifactorial. Both high grade venous stenosis and cerebral hyperemia are common in childhood hydrocephalus. High grade stenosis was noted to be a risk factor for conservative management failure. Hyperemia was a good prognostic indicator.

Background Children referred to a tertiary hospital for the indication, “rule out idiopathic intracranial hypertension (IIH)” may have an increased risk of raised venous sinus pressure. An increase in sinus pressure could be due to obesity, venous outflow stenosis or cerebral hyperemia. The purpose of this paper is to define the incidence of each of these variables in these children. Methods Following a data base review, 42 children between the ages of 3 and 15 years were found to have been referred over a 10 year period. The body mass index was assessed. The cross sectional areas and circumferences of the venous sinuses were measured at 4 levels to calculate the hydraulic and effective diameters. The arterial inflow, sagittal and straight sinus outflows were measured. Automatic cerebral volumetry allowed the brain volume and cerebral blood flow (CBF) to be calculated. The optic nerve sheath diameter was used as a surrogate marker of raised intracranial pressure (ICP). The sagittal sinus percentage venous return was used as a surrogate marker of elevated venous pressure. Age and sex matched control groups were used for comparison. Results Compared to controls, the obesity rates were not significantly different in this cohort. Compared to controls, those at risk for IIH had a 17% reduction in transverse sinus and 14% reduction in sigmoid sinus effective cross sectional area (p = 0.005 and 0.0009). Compared to controls, the patients at risk for IIH had an arterial inflow increased by 34% (p < 0.0001) with a 9% larger brain volume (p = 0.02) giving an increase in CBF of 22% (p = 0.005). The sagittal and straight sinus venous return were reduced by 11% and 4% respectively (p < 0.0001 and 0.0009) suggesting raised venous sinus pressure. Forty five percent of the patients were classified as hyperemic and these had optic nerve sheath diameters 17% larger than controls (p < 0.0002) suggesting raised ICP. Conclusion In children with the chronic headache/ IIH spectrum, the highest associations were with cerebral hyperemia and mild venous sinus stenosis. Obesity was not significantly different in this cohort. There is evidence to suggest hyperemia increases the venous sinus pressure and ICP.

BACKGROUND AND PURPOSE: Chronic hydrocephalus is associated with dilated ventricles despite a normal intracranial pressure. In idiopathic intracranial hypertension, the ventricles are normal despite an elevated intracranial pressure. This apparent paradox has largely remained unexplained. It is suggested that a pressure difference between the superficial and deep venous territories of the brain could account for the variation between the 2 diseases. The purpose of this paper is to investigate the cause of this pressure difference. MATERIALS AND METHODS: Using MR phase-contrast imaging, we calculated the hydraulic diameters of the sagittal and straight sinuses in 21 patients with hydrocephalus, 20 patients with idiopathic intracranial hypertension, and 20 age-matched controls. The outflow resistance of each sinus was estimated using the Poiseuille equation. The outflow pressure was estimated using the flow data. A smaller subset of the patients with hydrocephalus had these studies repeated after successful shunt insertion. RESULTS: In hydrocephalus, the sagittal sinuses were 21% smaller than those in controls (P Ͻ .001); the straight sinuses were not significantly different. In idiopathic intracranial hypertension, both sinuses were not significantly different from those of controls. The pressure drop from the sagittal sinus to the end of the straight sinus was elevated by 1.2 mm Hg in hydrocephalus (P ϭ .001) but not significantly different from that in controls in idiopathic intracranial hypertension. Shunt insertion dilated the sagittal sinuses in hydrocephalus, leaving them 18% larger than normal and eliminating the transvenous pressure change. CONCLUSIONS: There is a transvenous pressure difference in hydrocephalus that is absent in idiopathic intracranial hypertension. This difference is eliminated by shunt insertion. The findings may have a bearing on ventricular dilation.

Background: Multiple sclerosis (MS) is associated with a breakdown in the intracranial pulse wave dampening or windkessel effect. This is manifest by an increase in the arterial stroke volume and a decrease in the dampening afforded by both the CSF displaced into the spinal canal and the blood displaced by the venous sinus pulsation. There is evidence that the reduction in compliance of the sagittal and straight sinuses in MS is caused by an increase in venous pressure despite the jugular bulb pressures being normal. This implies MS patients have a venous outflow stenosis somewhere between the torcular and jugular bulbs. The purpose of the current study is to define the site, significance and cause of these stenoses. Methods: 50 patients with MS were prospectively recruited from an MS clinic and compared to 50 matched control patients. Using 3DT1 post contrast images, a survey of the venous sinuses was performed looking for the narrowest portion of the sinuses in each of 4 segments from the sagittal sinus to jugular bulbs. The cross sectional areas and wetted circumferences of the venous sinuses were measured at each site to calculate the minimum hydraulic and effective diameters. The BMI, optic nerve sheath diameters and pituitary heights were measured. Statistical analysis was performed using non-parametric methods and was assessed using α≤0.05. Results: Compared to controls, the MS patients' sagittal sinuses were 24% larger in cross-section (p=0.0001) with an 18% larger wetted circumference (p=0.0001). The MS patients' transverse sinuses had an average effective stenosis of 38% by area (p<0.0001) with 8/50 patients having a high grade stenosis of >65% by area and 16/50 a low grade stenosis of between 40-65% by area compared to 1/50 low grade stenoses in this segment in the controls. The commonest cause of the stenosis was a giant arachnoid granulation. The optic nerve sheaths were larger in MS than controls (p=0.0006). Comparing MS patients with transverse sinus stenosis to those without, the pituitary height was 16% smaller and BMI 25% larger (p=0.02 and 0.003 respectively) Conclusion: In patients with MS, the reduction in venous sinus compliance is associated with venous outflow stenoses in the transverse sinuses which increases the upstream venous pressure and dilates the sagittal sinuses. This finding suggests a continuum exists between MS and idiopathic intracranial hypertension.

Background It has been shown that idiopathic intracranial hypertension (IIH) in children is associated with cerebral hyperemia, which induces an increase in cerebral venous pressure. The current literature suggests venous pressure scales with blood flow in a linear fashion, however, a linear relationship would not raise the pressure high enough to induce IIH. There is, however, some evidence to suggest that this relationship could be quadratic in nature. The purpose of this paper is to characterize the relationship between cerebral blood flow and the pressure drop across the cerebral venous system. Methods 10 CT venogram data sets were collected for this study, with 5 useable geometries created. Computational fluid dynamics (CFD) models were generated using these geometries, with 10 simulations conducted per patient. The flow rates tested ranged from 200 mL/min to 2000 mL/min. 3D pressure and velocity streamline distributions were created and analyzed for each CFD model, with pressure drops across the cerebral venous system determined. The effective and hydraulic diameters were determined at the superior sagittal sinus, transverse sinus and both proximal and distal sigmoid sinuses. Results A quadratic relationship between blood flow and sinus pressure was found, with correlations of 0.99 or above in all five patients. The presence of vortical blood flow was found to explain this trend, with fluid curl and pressure drop correlations being above 0.97. This suggests that the presence of high blood flow should be considered in the diagnostic workup of IIH. Conclusions The cerebral venous sinus blood flow and pressure response relationship are quadratic in nature, with the major cause of this being the degree of rotation induced in the flow. The elevated blood flow found in children with IIH can explain the increased ICP that is found, secondary to the increase in venous pressure that develops.

The cross-sectional area of the superior sagittal sinus (SSS) is larger in multiple sclerosis than normal and correlates with disease severity and progression. The sinus could be enlarged due to a decrease in the pressure difference between the lumen and the subarachnoid space, an increase in wall thickness or increased wall stiffness. The cross-sectional area of the SSS and straight sinus (ST) were measured in 103 patients with multiple sclerosis and compared to 50 controls. The cross-sectional area of the SSS and ST were increased by 20% and 13% compared to the controls (p = 0.005 and 0.02 respectively). The deflection of the wall of the sinus was estimated. The change in pressure gradient, wall thickness or elastic modulus between groups was calculated by modelling the walls as simply supported beams. To account for these findings, the modelling suggests either a 70% reduction in transmural venous pressure or a 2.4 fold increase in SSS wall stiffness plus an 11% increase in wall thickness or a combination of changes. An increase in sinus pressure, although the most straight forward possibility to account for the change in sinus size may exist in only a minority of patients. An increase in sinus wall stiffness and thickness may need further investigation.

Spaceflight associated neuro-ocular syndrome (SANS) alters the vision of astronauts during long-duration spaceflights. There is controversy regarding SANS being similar to patients with idiopathic intracranial hypertension (IIH). IIH has been shown to be due to an elevation in venous sinus pressure. The literature suggests an increase in jugular vein pressure secondary to a headward shift of fluid occurs in SANS but this may not be enough to significantly alter the intracranial pressure (ICP). The literature regarding cardiac output and cerebral blood flow (CBF) in long-duration spaceflight is contradictory, however, more recent data suggests increased flow. Recent modelling has shown that an increase in CBF can significantly increase sinus pressure. The purpose of the present paper is to review the SANS vascular dynamics literature and through mathematical modelling suggest the possible underlying cause of SANS as an elevation in venous sinus pressure, secondary to the redistribution of fluids towards the head, together with a significant increase in pressure drop across the venous system related to the CBF.

Background: In a previous study, multiple sclerosis (MS) was found to be associated with an increase in intracranial arterial pulsation volume and a reduction in venous sinus compliance, affecting pulsation dampening. There was a suggestion that the reduction in compliance of the sagittal sinus in MS was caused by an increase in venous pressure, secondary to transverse sinus stenosis. Some differences were noted depending on the gender of the patients, however, the original study was relatively underpowered for further sub-classification. The purpose of the current study is to enroll a larger number of patients to allow sub-classification on gender and disease type to further evaluate the markers of possible venous pressure alteration. Methods: 103 patients with MS were prospectively recruited from an MS clinic and compared to 50 matched non-MS patients. Using 3DT1 post contrast images, the sagittal sinus cross-sectional area was measured. The narrowest portion of the transverse sinuses was located and the cross sectional areas and wetted circumferences were measured to calculate the minimum hydraulic and effective diameters. The jugular bulb heights were measured. Voxel wise brain morphometry was performed to evaluate atrophy. Statistical analysis was performed using non-parametric methods and was assessed using α≤0.05.Results: Compared to controls, the MS patients' sagittal sinuses were 23% larger in cross-section (p<0.0001), the transverse sinuses had an average effective stenosis of 39% by area (p<0.0001) and there was a 62% increase in jugular bulb height (p=0.0001). The MS patients showed a reduction in normalized grey matter volume of 2.8% (p= 0.0001). Males with MS showed worse outcomes compared to females, with an increased EDSS and grey matter loss and had a 23% larger sagittal sinus area (p=0.02), 22% higher jugular bulb height (p=0.03) but a lower transverse sinus stenosis percentage (19% vs 48%, p<0.0001). Progressive forms of MS also had worse outcomes and had a 19% larger sagittal sinus area (p=0.04) compared to relapsing remitting MS. Conclusion:In this larger cohort, worse outcomes in both males and progressive forms of MS were associated with larger sagittal sinuses. The possible cause of the altered sinus pressure in females was narrower transverse sinuses. In males, higher jugular bulbs may be associated with increased venous sinus pressure.