The role of dural sinus stenosis in idiopathic intracranial hypertension pathogenesis: the self-limiting venous collapse feedback-loop model

In recent years the efficacy of endovascular venous stenting in idiopathic IIH treatment has been consistently reported, strongly suggesting that sinus stenosis should be viewed as a causative factor rather than a secondary phenomenon. We propose that in subjects carrying one or more collapsible segments of large cerebral venous collectors and exposed to a number of different promoting factors, sinus venous compression and cerebrospinal fluid (CSF) hypertension may influence each other in a circular way, leading to a new relatively stable venous/CSF pressures balance state at higher values. The mechanism relay on self-limiting venous collapse (SVC) feedback-loop between the CSF pressure, that compresses the sinus, and the consequent venous pressure rise, that increases the CSF pressure. The result is the "coupled" increase of both pressure values, a phenomenon not expected in presence of sufficiently rigid central veins. Once the maximum stretch of venous wall is reached the loop stabilize at higher venous/CSF pressure values and become self-sustaining, therefore persisting even after the ceasing of the promoting factor. Notably, the SVC is reversible provided an adequate perturbation is carried to whichever side of the loop such as sinus venous stenting, on one hand, and CSF diversion or even a single CSF withdrawal by lumbar puncture (LP), on the other. The SVC model predicts that any condition leading to an increase of either, cerebral venous pressure or CSF pressure may trigger the feedback loop in predisposed individuals. Migraine with and without aura, a disease sharing with IIH a much higher prevalence among women of childbearing age, is associated with waves of significant brain hyperperfusion. These may lead to the congestion of large cerebral venous collectors and could represent a common SVC promoting condition in susceptible individuals. The SVC model give reason of the high specificity and sensitivity of sinus stenosis as IIH predictor and of the multiplicity of the factors that have been found associated with IIH. Moreover it might explain why, among the sinus stenosis carriers, young and overweight women are at higher risk of developing the disease. Finally, the SVC model fully explain the enigmatic longstanding remissions that can be commonly observed after a single LP with CSF subtraction in IIH with or without papilledema.