The putative role of brain lymphatic system in ménière disease pathogenesis

Ménière’s disease (MD) is a chronic illness of the inner ear with an incidence, in Europe about 50-200/100.000 a year [1]. It is characterised by intermittent episodes of vertigo lasting from minutes to hours, with sensor neural, usually fluctuating, hearing loss, tinnitus, and aural pressure. Diagnosis is mainly based on clinical course and MD is usually considered as a multifactorial disease, thus there are not yet evidences for a specific treatment [2,3]. The inner ear comprehends hearing and balance sensory organs it is deeply embedded into the petro us part of the temporal bone, its blood supply is provided through the labyrinthine artery, a branch of the anterior inferior cerebellar artery (>85% cases) or basilar artery (<15% cases), its drainage is formed by the labyrinthine veins that flow, via the inferior petro us sinus, into the Internal Jugular Veins (IJVs) [4]. The luminal compartment of the inner ear, known as the endolymphatic space, is separated by the abluminal compartment, the perilymphatic space, through highly specialized epithelial cells with tight junctions. The fluid volume within the bony labyrinth remains constant. Changes in the volumes of the endolymphatic and perilymphatic compartments are responses to osmotic gradients between the compartments themselves [5]. MD is characterized by impairment of this balance between the compartments causing the so called Endolymphatic Hydrops (EH), usually considered the pathogenesis of MD. The EH associated with Ménière’s disease has been correlated to many etiological factors able to alter the endolymphatic homeostasis, such as abnormalities in end lymph production or absorption [6], cervico-cephalic venous drainage impairment [7-9] genetic anomalies, allergies [10], viral infections [11] and autoimmunity or inflammatory processes [12]. It has been suggested that certain cases of MD may have an altered immunological background, which may be attributable to an autoimmune mechanism that depends on humoral and/or cellular responses leading to an altered blood-labyrinth barrier [13]. The underlying mechanism of EH is still debated, with some researches in favour of a purely hydraulic mechanism and others hypothesizing a control mechanism of ionic balance. Hydraulic hypothesis supports ES surgical treatment while Control hypothesis a pharmachologic and dietary approach.