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.