Endolymphatic hydrops is a disorder of the vestibular system of the inner ear. It stems from abnormal fluctuations in the fluid called endolymph, which fills the hearing and balance structures of the inner ear. If the inner ear is damaged by disease or injury, the volume and composition of the inner-ear fluid can fluctuate with changes in the body's fluid and electrolyte levels. This fluctuation causes the symptoms of hydrops -- pressure or fullness in the ears, tinnitus (ringing in the ears), hearing loss, dizziness, and imbalance. Endolymphatic hydrops may occur as a result of a head blow, infection, degeneration of the inner ear, allergy, or (rarely) a tumour, or the cause may be unknown.
In a normal inner ear, the endolymph is maintained at a constant volume and contains specific concentrations of sodium, potassium, chloride, and other electrolytes. This fluid bathes the sensory cells of the inner ear and allows them to function normally.