Quick definition
Endolymph is the fluid that fills the membranous labyrinth of the inner ear — the cochlear duct and the semicircular canals. Its movement, driven by head motion or by sound, is what the hair cells of the inner ear convert into the neural signals that produce hearing and balance.
Medical definition
Endolymph is a potassium-rich, sodium-poor fluid (approximately 150 mEq/L K+, 1 mEq/L Na+) — the inverse composition of most extracellular fluids. This unusual ionic composition is maintained by the stria vascularis and is critical for cochlear and vestibular hair cell function. Endolymph sits inside the membranous labyrinth, with perilymph (resembling cerebrospinal fluid) surrounding it.
Why it matters in vertigo and balance disorders
When endolymph volume rises abnormally — endolymphatic hydrops — the result is Meniere disease: episodic vertigo, fluctuating hearing loss, tinnitus, and ear fullness. When endolymph leaks (as in a perilymph fistula, which is technically a perilymph problem but can affect endolymph dynamics) the result is pressure-triggered vertigo.
Where I see this in clinic
For Meniere patients, much of the conversation in clinic is about reducing endolymphatic pressure — low-salt diet, careful diuretic use under supervision, and intratympanic interventions when the disease does not respond. The fluid I am trying to manage is endolymph.
Related terms
Part of: Vestibular and ENT Glossary — A to Z of vestibular, balance, and ENT terms by Dr. Prateek Porwal.
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