Cause

          The inner ear (cochlea and semicircular canals) is composed of two types of fluid called the endolymph and the perilymph.  They differ in their sodium and potassium content and this difference in composition is what is responsible for the electrical charge of the inner ear.

          The endolymph is formed within the cochlea and circulates throughout the inner ear.  An extension of the inner ear, known as the endolymphatic duct and sac, lies against the dura or covering of the brain.  Within the endolymphatic sac, endolymph is filtered through to the connective tissue around the sac.  From here, the fluid can enter blood vessels or enter the spinal fluid space.  The volume of endolymph is extremely small and is measured in nanoliters.

          The current theory is that Meniere’s disease symptoms are caused by an imbalance in fluid pressure between the endolymphatic and perilymphatic chambers.  The endolymph is believed to build up excess fluid and pressure.  The membrane that separates the two chambers houses the nervous tissue or hearing and balance.  Therefore, fluctuations in pressure cause hearing and balance disturbances.

          Once the pressure reaches a critical level, the thin membrane ruptures.  The mixing of the endolymph and the perilymph causes a “short circuiting” of the inner ear because they are chemically different.  This sends an unbalanced message down the vestibular nerve to the brain and the patient experiences severe spinning vertigo, nausea, hearing loss, Tinnitus, and a full feeling in the ear. 

          The reason for the buildup of endolymph is unknown, but it is speculated to be a defect in the absorbance in the endolymphatic sac.