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Topic

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Cochlea

The cochlea is a spiral-shaped, bony structure within the inner ear, crucial for hearing. Shaped like a snail shell, it transforms sound waves into electrical signals for the brain. The cochlea is housed in the petrous part of the temporal bone, measuring approximately 9 mm in diameter and 5 mm in height. It consists of three fluid-filled chambers—the scala tympani, scala vestibuli, and scala media (cochlear duct)—which play key roles in the auditory transduction process. Its highly organized anatomy and delicate membranous structures are critical for the perception of sound and are best appreciated with high-resolution imaging modalities.

Function:

  • Converts mechanical sound vibrations into nerve impulses via hair cells.

  • Transmits auditory signals from the oval window to the auditory nerve (cochlear nerve).

  • Separates different sound frequencies along its spiral (tonotopic organization).

MRI Appearance:

T1-Weighted Images:

  • The cochlea appears as a small, low-signal (dark) structure within the high-signal (bright) marrow of the petrous temporal bone.

  • Fluid-filled spaces (endolymph and perilymph) are hypointense (dark) on T1.

  • Enhancing cochlea may indicate abnormality (e.g., labyrinthitis or post-contrast).

3D T2-Weighted Images (e.g., CISS, FIESTA):

  • The cochlea is sharply delineated as a hyperintense (bright) spiral structure within the petrous bone.

  • Excellent visualization of the internal architecture, including the modiolus and turns of the cochlea.

  • Fluid-filled chambers are very bright, surrounded by the dark bony labyrinth.

  • Useful for detecting membranous labyrinth abnormalities, congenital anomalies, and cochlear nerve aplasia.

CT Appearance:

  • High-resolution temporal bone CT shows the cochlea as a dense, coiled, bony structure with about 2.5 turns.

  • The bony outline is well defined, and the modiolus (central axis) can be visualized.

  • CT is ideal for assessing bony abnormalities (fractures, otospongiosis, cochlear dysplasia, ossification).

  • The adjacent round and oval windows are also typically well seen.

MRI images

Cochlea MRI 3T axial image

MRI images

Cochlea MRI 3T coronal image

MRI images

Cochlea MRI 3T sagittal image