A Mathematical Model of Idiopathic Intracranial Hypertension Incorporating Increased Arterial Inflow and Variable Venous Outflow Collapsibility

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.