Topics

Topic

design image
Spiral canal of cochlea

The spiral canal of the cochlea, also known as the cochlear spiral canal, is the bony, helical tunnel within the petrous part of the temporal bone that houses the cochlear duct (scala media), scala vestibuli, and scala tympani. It winds around the modiolus, the central bony core of the cochlea, completing approximately 2.5 turns from base to apex.

This spiral osseous canal supports the delicate membranous labyrinth involved in hearing transduction, enabling mechanical vibrations to be converted into neural signals by the organ of Corti. Its shape, width, and compartments are essential for frequency discrimination and normal auditory function.

Synonyms

  • Cochlear spiral canal

  • Osseous cochlear canal

  • Bony cochlear spiral

Location and Structure

  • Situated within the petrous temporal bone, forming part of the bony labyrinth.

  • Spirals around the modiolus in a tightly coiled helix from the basal turn to the apex (helicotrema).

  • Composed of:

    • Scala vestibuli (superior)

    • Scala media (middle cochlear duct)

    • Scala tympani (inferior)

  • Bounded laterally by the spiral ligament and medially by the modiolus containing cochlear nerve fibers.

  • Includes the osseous spiral lamina, a bony shelf that partially divides the canal and supports the cochlear duct.

Relations

  • Medially: Internal auditory canal containing cochlear nerve fibers entering the modiolus

  • Laterally: Cochlear outer wall and spiral ligament

  • Superiorly: Vestibule of the inner ear

  • Inferiorly: Basal turn adjacent to the round window niche and tympanic cavity

  • Posteriorly: Vestibular structures and semicircular canals

Function

  • Houses the membranous cochlear duct, enabling sound transduction

  • Maintains separation of perilymph (scala vestibuli/tympani) and endolymph (scala media)

  • Provides structural support to the organ of Corti

  • Facilitates frequency mapping from high frequencies (base) to low frequencies (apex)

  • Ensures precise mechanical-to-electrical conversion of sound

Clinical Significance

  • Sensorineural hearing loss: May result from malformations or ossification

  • Cochlear nerve deficiency: Often evaluated via modiolus and canal morphology

  • Labyrinthitis or cochlear inflammation: Produces abnormal fluid signal on MRI

  • Otosclerosis: Basal turn involvement may cause conductive or mixed hearing loss

  • Cochlear implant planning: Requires precise assessment of canal patency and dimensions

  • Fractures: Temporal bone fractures may disrupt the cochlear canal or cause perilymph fistula

MRI Appearance

T1-weighted images (Pre-Contrast):

  • Bone: Very low signal (black), outlining the spiral canal

  • Perilymph fluid: Low-to-intermediate signal

  • Endolymph within cochlear duct: Similar low-to-intermediate signal

  • Modiolus: Intermediate signal due to nerve fibers and marrow pockets

  • Pathology:

    • Hemorrhage: high signal within perilymph spaces

    • Fibrosis/ossification: low-signal abnormal filling of canal spaces

T1 Fat-Sat Post-Contrast:

  • Normal:

    • Perilymph and endolymph: minimal enhancement

    • Modiolus: mild enhancement of vascular channels

  • Abnormal enhancement:

    • Labyrinthitis: diffuse or patchy enhancement of fluid spaces or modiolus

    • Neoplasms (e.g., schwannoma extension): focal or nodular enhancement along modiolus

    • Post-surgical or inflammatory changes: soft-tissue/vascular enhancement within cochlear turns

3D T2-Weighted Imaging (e.g., 3D T2 SPACE, FIESTA, CISS)

  • Fluid (perilymph and endolymph): Very bright, sharply outlining all cochlear turns

  • Bony spiral canal and modiolus: Dark low-signal structures forming a distinct helical contour

  • Cochlear nerve: Seen entering the modiolus from internal auditory canal

  •  

CT Appearance

Temporal Bone CT (Non-Contrast):

  • Best modality for cochlear bony anatomy

  • Bony spiral canal: High-attenuation dense bone forming distinct helical turns

  • Modiolus: Dense central core

  • Canal for cochlear nerve: Small opening into modiolus from internal auditory canal

  • Basal turn: Seen clearly adjacent to round window niche

  • Pathology:

    • Otosclerosis: Lucent foci near the cochlear capsule (fenestral or retrofenestral)

    • Cochlear dysplasia: Incomplete turns or broadened cochlear canal

    • Ossification: High-attenuation filling of perilymph spaces

    • Fractures: Disruption of canal continuity or pneumolabyrinth (air inside cochlea)

    • Cochlear implant planning: Assessment of patency and cochlear duct length

MRI image

Spiral canal of cochlea axial image 1

MRI image

Spiral canal of cochlea mri axial image