Endolymphatic

Endolymphatic refers to endolymph, the fluid contained within the membranous labyrinth of the inner ear, including the cochlear duct (scala media) and the vestibular labyrinth. The endolymphatic space is bounded by the walls of the membranous labyrinth and by the endolymphatic duct and sac, which connect to surrounding structures in the temporal bone.

Endolymph has a distinctive ionic composition, being high in potassium and low in sodium, and it generates a positive endolymphatic potential of about +80 millivolts relative to perilymph. The stria vascularis in the cochlea is a major site of endolymph production, while the vestibular apparatus contributes to the endolymphatic environment.

Functionally, the endolymphatic space supports the sensory hair cells of both the cochlea and vestibular organs by maintaining the electrochemical environment necessary for transduction of sound and head movement. Homeostasis is achieved through production, circulation, and resorption of endolymph, primarily via the endolymphatic sac.

Clinical relevance arises when regulation of endolymph is disturbed, leading to endolymphatic hydrops—the pathological distention of endolymphatic spaces. This condition is associated with Meniere's disease, which presents with vertigo, fluctuating sensorineural hearing loss, tinnitus, and aural fullness. Management focuses on symptom control and may include diuretics, dietary modifications, intratympanic therapies, or surgical interventions in selected cases.

See also: Endolymph, Endolymphatic sac, Endolymphatic duct, Meniere's disease.