Structure of the Cochlea, Pathologies of the Cochlea, Cochlear Malformations (Congenital, Trauma-Related Cochlear Injury

 The cochlea is a spiral-shaped, fluid-filled structure located in the inner ear. critical role in the sense of hearing.

🌀 Structure of the Cochlea:

• Shape: Resembles a snail shell; about 2.5 turns in humans.

• Divided into three fluid-filled chambers:

  1. Scala Vestibuli – contains perilymph.

  2. Cochlear Duct – contains endolymph and houses the Organ of Corti (the sensory organ of hearing).

  3. Scala Tympani – also contains perilymph.

👂 Function:

• Sound transmission:

1. Sound waves enter the cochlea via the oval window.

2. These waves create fluid movement inside the cochlea.

3. This movement stimulates hair cells in the Organ.

4. Hair cells convert mechanical vibrations into electrical signals.

5. Signals are transmitted to the brain via the auditory nerve.

MR COCHLEA

🔬 Clinical Significance:

• Damage to the cochlea or its hair cells can cause sensorineural hearing affect.

• Cochlear implants can be used in cases of severe hearing loss to directly stimulate the nerve.

🧠 Pathologies of the Cochlea

1. Sensorineural Hearing Loss (SNHL)

• Cause: Damage to cochlear hair cells or nerve.

• Types:

  • Noise-induced (e.g., loud music, machinery)

  • Age-related (Presbycusis)

  • Ototoxicity (due to drugs like aminoglycosides, cisplatin)

  • Congenital (e.g., genetic mutations)

2. Cochlear Malformations (Congenital)

• Examples:

  • Mondini dysplasia (incomplete cochlear turns)

  • Michel aplasia (complete absence of cochlea)

  • Common cavity deformity

• Detected by: CT or MRI of the inner ear

• Clinical Significance: Early-onset deafness

3. Labyrinthitis and Cochleitis

• Infectious inflammation of the cochlea (bacterial or viral)

• Symptoms: Sudden hearing loss, vertigo

• Causes: Meningitis, upper respiratory infections

• MRI: May show enhancement of cochlea (post-contrast)

4. Autoimmune Inner Ear Disease (AIED)

• Immune system attacks cochlear structures.

• Symptoms: Rapidly progressive SNHL, sometimes bilateral.

• Treatment: Steroids, immunosuppressants

5. Meniere’s Disease

• Cause: Excess endolymph in the cochlear duct

• Symptoms:

  • Fluctuating hearing loss

  • Tinnitus (ringing in ears)

  • Vertigo

• Imaging: MRI with delayed contrast can show endolymphatic hydrops

6. Cochlear Otosclerosis

• Abnormal bone growth around cochlea and stapes footplate.

• Causes progressive conductive or mixed hearing loss

• May involve otic capsule.

• CT Temporal Bone is useful for diagnosis.

7. Trauma-Related Cochlear Injury

• Fractures (temporal bone) can damage cochlea.

• Can result in perilymph fistula, sudden SNHL, or vertigo.

8. Tumors

• Rarely, cochlear schwannomas or intralabyrinthine tumors may arise.

• Can mimic SNHL or Meniere’s disease.

• Diagnosed with contrast-enhanced MRI.