A Model for IIH, IIHWOP, and the Generation of Certain Pathological ICP Wave-forms

Idiopathic intracranial hypertension (IIH) is a syndrome of unknown cause characterized by elevated intracranial pressure (ICP). While imaging often reveals a stenosis of the transverse sinuses, the role of this feature in IIH has been in dispute. Many patients with chronic daily headache have been found to actually be suffering from a milder form of IIH without papilledema (IIHWOP). These patients often demonstrate hypertensive B-waves and plateau-like waves upon continuous ICP monitoring. Recently, we presented modeling studies which suggest that the sinus stenosis and hypertension of IIH are physiological manifestations of a stable state of elevated pressures that exists when the transverse sinus is sufficiently collapsible. Many of the features of IIH were explained by this model but the prevalence of pathological ICP wave-forms observed in IIHWOP remained unresolved. The model presented here is a modified version of a previous model with a semi-collapsible sinus represented by a refined downstream Starling-like resistor based on experimental data. The qualitative behavior of this model is presented in terms of the collapsibility of the transverse sinus. For a sufficiently rigid sinus there is a unique stable state of normal pressures. As the degree of collapsibility increases, there is a Hopf bifurcation, the normal state becomes unstable, low frequency, high amplitude ICP waves prevail, and small perturbations can lead to hypertensive ICP spikes. As the collapsibility increases further, so does the duration of the waves, until they are replaced by two stable states: one of normal pressures and one of elevated pressures. In this parameter domain, temporary perturbations can now cause permanent transitions between states. The model presented here retains the capability of our previous model to elucidate many features of IIH and additionally provides insight into the prevalence of the low frequency, high amplitude waves observed in IIHWOP.