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Cochlear Canaliculus

The cochlear canaliculus, also known as the cochlear aqueduct, is a narrow bony channel connecting the basal turn of the cochlea to the posterior cranial fossa. It transmits the perilymphatic duct, allowing communication between the subarachnoid space and the perilymphatic space of the inner ear.

Although its physiological role is limited in adults, the canaliculus is clinically important because it forms a potential pathway for infection, CSF leak, meningitis spread, and pressure transmission abnormalities. Its visualization is essential in evaluating inner ear malformations, pulsatile tinnitus, and congenital perilymphatic communication disorders.

Synonyms

  • Cochlear aqueduct

  • Aqueductus cochleae

  • Perilymphatic duct canal

Location and Structure

  • Begins at the posterior aspect of the basal turn of the cochlea

  • Runs posteriorly and inferiorly through the petrous temporal bone

  • Opens into the posterior cranial fossa near the jugular foramen

  • Contains the perilymphatic duct, connective tissue, and small vessels

  • Narrow, variable in size, sometimes partially or completely obliterated

Relations

  • Anteriorly: Basal turn of the cochlea

  • Posteriorly: Posterior cranial fossa dura

  • Superiorly: Internal auditory canal and vestibule

  • Inferiorly: Jugular bulb and lower petrous bone

  • Lateral: Cochlear structures

  • Medial: Subarachnoid space of posterior fossa

Function

  • Provides an anatomical connection between the perilymph and subarachnoid space

  • Helps maintain inner ear fluid homeostasis early in development

  • Potential conduit for CSF pressure transmission

  • Acts as a pathway in pathological conditions including meningitis and perilymphatic fistula

Clinical Significance

  • Enlarged cochlear aqueduct: Associated with certain congenital inner ear malformations

  • CSF leak: May occur through an abnormally patent canaliculus

  • Recurrent meningitis: Resulting from abnormal communication between CSF and perilymph

  • Temporal bone fractures: May disrupt the aqueduct

  • Surgical relevance: Important in skull base and cochlear implant planning

  • Imaging relevance: Key structure in metabolic, congenital, and inflammatory inner ear disorders

MRI Appearance

T1-weighted images

  • Bony canal: Low signal due to dense cortical bone

  • Perilymphatic duct: Usually too small to visualize directly

  • Surrounding marrow spaces: Bright fatty signal

  • Pathology:

    • Fluid accumulation or patency may appear hypointense linear tract

    • Adjacent inflammation: intermediate or enhancing soft-tissue signal

T2-weighted images

  • Canal lumen: Typically hypointense (bone)

  • Perilymph or CSF-related fluid, if visualized: Bright T2 signal

  • Enlarged aqueduct: Better seen as a bright fluid-filled channel

  • Pathology:

    • Inflammation or abnormal patency: hyperintense signal

    • Temporal bone abnormalities: altered T2 appearance of adjacent structures

3D T2 (SPACE/CISS/FIESTA)

  • Provides the best visualization of the cochlear canaliculus

  • Canal appears as a thin, low-signal bony track

  • Perilymphatic duct, if patent, appears as a thin bright linear fluid signal

  • Excellent for:

    • Inner ear malformations

    • Aqueduct enlargement

    • Preoperative assessment of cochlear implants

T1 Fat-Sat Post-Contrast

  • Normal canal: No enhancement

  • Surrounding dura or periaqueductal tissue may enhance faintly

  • Pathology:

    • Meningitis or inflammation: linear or nodular enhancement near posterior opening

    • Post-traumatic granulation: irregular enhancing focus

    • CSF leak: Indirect signs such as enhancement of adjacent soft tissues

CT Appearance

Non-Contrast Temporal Bone CT

  • Best modality to visualize the bony canal

  • Cochlear canaliculus appears as a tiny, well-defined bony channel

  • Seen connecting the posterior cochlear basal turn to posterior cranial fossa

MRI image

Cochlear canaliculus MRI axial image