Topics

Topic

design image
Scala vestibuli

The scala vestibuli is one of the three major fluid-filled chambers of the cochlea, located superiorly within the spiral labyrinth of the inner ear. It begins at the oval window, where stapes footplate vibrations enter, and spirals upward to the helicotrema at the apex of the cochlea, where it communicates with the scala tympani.

It contains perilymph, a fluid similar to extracellular fluid, and plays a critical role in mechanical conduction of sound waves transmitted from the middle ear into the cochlear spiral. The scala vestibuli lies above Reissner’s membrane, which separates it from the endolymph-filled scala media.

Its delicate anatomy and fluid composition make it essential in auditory physiology and important in evaluating cochlear implants, congenital inner-ear malformations, infections, and ossification after labyrinthitis.

Synonyms

  • Vestibular scala

  • Upper cochlear chamber

  • Perilymphatic vestibular duct

Location and Structure

  • Position: Upper perilymph-filled chamber within the bony cochlea.

  • Beginning: At the oval window (fenestra vestibuli).

  • Course: Spirals upward through the cochlear turns—basal, middle, and apical.

  • Termination: At the helicotrema, where it merges with the scala tympani.

  • Fluid: Filled with perilymph, high in sodium and low in potassium.

  • Boundaries:

    • Inferiorly: Reissner’s membrane

    • Laterally: Cochlear bony wall

    • Medially: Modiolus

Relations

  • Medially: Modiolus containing spiral ganglion and cochlear nerve fibers

  • Inferiorly: Scala media (cochlear duct) separated by Reissner’s membrane

  • Superiorly: Outer bony wall of cochlea

  • Laterally: Vestibule at its origin

  • Posteriorly: Round window and scala tympani (connected indirectly via helicotrema)

Function

  • Primary conduit for perilymphatic sound transmission from oval window to apex

  • Transfers vibratory energy toward scala tympani to move the basilar membrane

  • Maintains perilymph homeostasis essential for normal cochlear mechanics

  • Protects hair cell function by stabilizing fluid pressure within cochlea

  • Important in inner-ear pressure equalization through helicotrema

Clinical Significance

  • Labyrinthitis ossificans: Scala vestibuli often shows early ossification

  • Congenital malformations: Enlarged vestibular aqueduct or hypoplastic cochlea

  • Superior semicircular canal dehiscence: Affects perilymph dynamics near vestibule

  • Cochlear implant planning: Patency of scala vestibuli and tympani is essential

  • Fluid signal abnormalities: Seen in infection, fibrosis, hemorrhage, and trauma

  • Perilymph fistula: May involve oval window region affecting scala vestibuli entry

MRI Appearance

T1-weighted (Pre-Contrast)

  • Perilymph in scala vestibuli: Low-to-intermediate signal

  • Bony cochlear walls: Very low (black)

  • Cochlear modiolus: Intermediate signal

  • Hemorrhage or proteinaceous fluid: May show abnormally high T1 signal

  • Ossification/fibrosis: Appears as low-signal filling defects

T1-weighted (Post-Contrast, Fat-Sat)

  • Normal perilymph: No intrinsic enhancement

  • Enhancement patterns:

    • Labyrinthitis: Smooth or patchy enhancement around perilymphatic spaces

    • Infection or inflammation: Enhancing cochlear walls or modiolar regions

    • Neoplastic infiltration: Irregular enhancement extending into cochlea

    • Postoperative changes: Enhancement along electrode tracts in cochlear implants

T2-weighted (Standard + 3D High-Resolution)

  • Perilymph: Very bright hyperintense fluid

  • Reissner’s membrane: Usually not visible unless pathologic

  • Bony boundaries: Low-signal margins sharply outlining scala vestibuli

  • 3D T2 sequences (SPACE, DRIVE, FIESTA, CISS):

    • Scala vestibuli appears as a bright, sharply defined fluid channel

    • Cochlear turns clearly separated

    • Essential for assessing cochlear patency, fibrosis, or obstruction

  • Pathology:

    • Labyrinthitis ossificans: Partial or complete loss of bright T2 signal

    • Fibrosis: Intermediate signal replacing perilymph

    • Hemorrhage: Heterogeneous intermediate-to-low T2 signal

CT Temporal Bone Appearance

Non-Contrast CT

  • Bony boundaries: High-density, sharply defined cochlear turns

  • Scala vestibuli itself: Appears as a low-attenuation lumen (fluid-filled)

  • Normal findings:

    • Well-formed cochlear turns

    • Patent scala vestibuli and tympani

  • Pathology:

    • Labyrinthitis ossificans: Dense calcification or ossification replacing lumen

    • Congenital cochlear hypoplasia: Reduced cochlear turns or enlarged vestibule

    • Otosclerosis (fenestral or cochlear): Hypodense focus near oval window or cochlear capsule

    • Temporal bone fractures: Disruption through cochlear turns or vestibule

MRI image

Scala vestibuli MRI axial image