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Grant A. Bateman

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Grant A. Bateman

Object

Findings in animal models of noncommunicating hydrocephalus have suggested that a reduction in compliance of the superior sagittal sinus, an elevation in venous outflow pressure, and the development of venous collateral flow may be associated with this condition. Although elevated venous pressure is known to cause hydrocephalus in children, this mechanism has fallen out of favor as a theory in adults.

Methods

Twenty-one patients with late-onset idiopathic aqueductal stenosis (LIAS) underwent magnetic resonance imaging with flow quantification measuring the degree of ventricular enlargement, sulcal compression, total blood inflow, superior sagittal/straight sinus outflow, aqueduct flow, arteriovenous delay (AVD), and the extent of collateral venous flow. Data obtained in these patients were compared with those obtained in 21 age-matched control individuals.

Results

There was a reduction in compliance in the patients with LIAS in whom the AVD decreased by 50% (p = 0.01). The arterial inflow and the straight sinus outflow were normal, but the sagittal sinus outflow was reduced by 23% (p = 0.001). This indicated that significant collateral venous outflow pathways were draining blood away from the superficial but not the deep drainage system.

Conclusions

Similar to the animal models, patients with LIAS exhibit a reduced venous compliance and an elevation in venous collateral flow. Together, these findings suggest that an elevation in venous pressure may be associated with this disease process. A review of the literature has indicated that only subtle differences may exist in the pathophysiology among patients with LIAS, normal-pressure hydrocephalus, and idiopathic intracranial hypertension.

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Harold L. Rekate

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Grant A. Bateman, Robert L. Smith and Sabbir H. Siddique

Object

Both idiopathic intracranial hypertension (IIH) in adults and idiopathic hydrocephalus in children have been shown to involve elevations in venous pressure that resolve once the cerebrospinal fluid pressure is reduced. It has been assumed that the venous pressure elevations in both conditions are not hemodynamically significant, but measurement of venous collateral flow in IIH has shown these pressure elevations to be of consequence. The authors used the same methodology to see if the venous pressure elevations noted in childhood hydrocephalus are important.

Methods

Fourteen patients with idiopathic childhood hydrocephalus underwent magnetic resonance imaging with flow quantification. The degree of ventricular enlargement, total blood inflow, and superior sagittal/straight sinus outflow was measured. The degree of collateral venous flow was calculated for each venous territory. The findings were compared with findings in 14 age-matched controls.

Results

In children with hydrocephalus the cerebral blood inflow was normal, but the superior sagittal sinus (SSS) and straight sinus outflows were reduced by 27% and 38%, respectively, compared with measurements in controls (p = 0.03 and 0.002). These findings suggest that approximately 150 ml of blood per minute was returning via collateral channels from that portion of the brain drained by the SSS, and 60 ml/minute was returning from collaterals in the deep venous territory.

Conclusions

Similarly to patients with IIH, children with hydrocephalus show a significant elevation in collateral venous flow, indicating that the same venous pathophysiological process may be operating in both conditions. Whether or not the ventricles dilate may depend on the differences in brain compliance between adults and children.

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Grant A. Bateman

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Grant A. Bateman, Scott A. Stevens and Jesse Stimpson

Object

A collapsible segment in the venous outflow has been noted in many patients with idiopathic intracranial hypertension (IIH). Mathematical modeling has shown that these collapsible segments can account for the elevated cerebrospinal fluid (CSF) pressures associated with IIH. However, the model required an elevated outflow resistance of up to 10 times normal to predict the CSF pressures actually found clinically. Measurement of blood flow in patients with IIH has shown that inflow rates vary, with higher rates noted in patients with lesser outflow stenoses. The aim of this work was to extend a simple model of cerebral hydrodynamics to accommodate a collapsible sinus and elevations in cerebral blood flow in accordance with in vivo measurements.

Methods

Forty patients with IIH underwent MR imaging in which the degree of stenosis on MR venography was compared with the total blood inflow by using MR flow quantification. The relative outflow resistance in IIH was estimated using the CSF opening pressure. The patients were compared with 14 age-matched control individuals.

Results

Patients were divided into 3 groups based on MR venography appearances (minimal stenosis, stenosis of 40–70% and > 70% stenosis). In vivo measurements suggested a relative resistance elevation of 2.5 times normal, 4.2 times normal, and 4.8 times normal in the 3 groups, respectively. There was an increased inflow of 1.56 times normal, 1.28 times normal, and 1.19 times normal in these groups.

Conclusions

The model correctly predicted the CSF pressures noted in vivo, suggesting that high arterial inflow is required for patients with low-grade stenoses to be symptomatic.

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Editorial

Hyperemic hydrocephalus

Harold L. Rekate

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Grant Bateman

Object

In the majority of adults with idiopathic intracranial hypertension (IIH), there is an elevation in venous pressure associated with a venous outflow stenosis. In about 15% of IIH patients the elevated venous pressure is associated with an elevation in blood flow but little or no evidence of a stenosis. Venostenotic IIH and idiopathic hydrocephalus in children with a normal blood inflow have been shown to be equivalent. The aim of this study was to test whether children with hydrocephalus and an elevated arterial inflow have a vascular pathophysiology that is analogous to the hyperemic form of IIH in adults.

Methods

Nine children with idiopathic hydrocephalus underwent MR imaging with flow quantification and were found to have arterial inflows 2 SDs above the mean for normal controls. Measurements of the head circumference, ventricular enlargement, total blood inflow, superior sagittal sinus (SSS)/straight sinus (SS) outflow, and the degree of collateral venous flow were performed. The results were compared with findings in 14 age-matched controls.

Results

In hyperemic hydrocephalus the cerebral blood inflow was elevated but the SSS and SS outflows were in the normal range. The sinus outflow as a percentage of the inflow was reduced by 8 percentage points in the SSS territory and 5 percentage points in the SS territory compared with findings in the controls (p = 0.04, p = 0.003, respectively), suggesting blood was returning via collateral channels.

Conclusions

Similar to patients with hyperemic IIH, children with hyperemic hydrocephalus show a significant elevation in collateral venous flow, indicating that the same venous pathophysiology may be operating in both conditions.

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Grant A. Bateman

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Grant A. Bateman

Symptomatic shunt malfunction without ventricular enlargement is known as slit ventricle syndrome (SVS). Patients presenting with this syndrome are not a homogeneous group. Of the 5 different types classified by Rekate, Type 1 is caused by CSF overdrainage and is associated with low pressures; Types 2 and 3 are associated with shunt blockage and elevated CSF pressures; Type 4 is cephalocranial disproportion that increases brain parenchymal pressure but not CSF pressure; and Type 5 is headache unrelated to shunt function. The low and normal CSF pressure types are relatively well understood, but the high-pressure forms are more problematic. In the high-pressure forms of SVS it is said that the lack of ventricular dilation is related to a reduction in brain compliance analogous to idiopathic intracranial hypertension or pseudotumor cerebri. Despite this, there is little evidence in the literature to support this conjecture. With this in mind, 3 cases of SVS associated with elevated CSF pressure are presented. The MR venogram findings and hemodynamics of these 3 cases are shown to be identical to those of pseudotumor cerebri. A literature review indicates that an underlying venous impairment may be functioning in the patients who re-present with small ventricles following shunt malfunction.