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.
Keywords: Idiopathic intracranial hypertension; Multiple sclerosis; Venous sinus stenosis.
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