Although its underlying cause and natural history are unknown, it is believed to result from abnormalities in the quantity, composition, and/or pressure of the endolymph (the fluid within the endolymphatic sac, a compartment of the inner ear).
Endolymphatic hydrops may be either primary or secondary. Primary idiopathic endolymphatic hydrops (known as Ménière’s disease) occurs for no known reason. Secondary endolymphatic hydrops appears to occur in response to an event or underlying condition. For example, it can follow head trauma or ear surgery, and it can occur with other inner ear disorders, allergies, or systemic disorders (such as diabetes or autoimmune disorders).
In a normal inner ear, the endolymph is maintained at a constant volume and with 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. In an inner ear affected by hydrops, these fluid-system controls are believed to be lost or damaged. This may cause the volume and concentration of the endolymph to fluctuate in response to changes in the body’s circulatory fluids and electrolytes.