Perilyympiä

Perilyympiä is Finnish for perilymph, the extracellular fluid that fills the perilymphatic spaces of the inner ear. It lies between the bony labyrinth and the membranous labyrinth, occupying the scala vestibuli and scala tympani, and it communicates with the cerebrospinal fluid through the cochlear aqueduct.

The perilymph is produced mainly by diffusion from blood plasma across the capillary walls of the inner ear, with a small contribution from surrounding fluids. Its composition is similar to extracellular fluid: high in sodium and low in potassium, with relatively little protein and an osmolarity close to that of plasma. This composition helps maintain ion balance around the sensory hair cells and supports the mechanical transmission of sound-induced vibrations.

Functionally, perilymph acts as a cushion and a conducting medium. It transmits mechanical energy from the stapes at the oval window through the scala tympani to the endolymph within the membranous labyrinth, enabling the activation of hair cells in the cochlea. It also participates in homeostasis of ionic composition in the inner ear fluids and serves as a reservoir that can respond to pressure changes.

Clinical relevance includes perilymph fistula, a rupture that can lead to vertigo and sensorineural hearing loss after trauma or barotrauma. Diagnosis is clinical, supported by audiological testing; treatment ranges from conservative management to surgical repair of the leak, depending on severity. Perilymphatic disturbances are distinct from endolymphatic disorders such as Menière’s disease, which involve the endolymph compartment.