Which nerve, if irritated, can cause tinnitus (ringing ears)?

Irritation of the Vestibulocochlear Nerve (CN VIII) Causes Tinnitus

The vestibulocochlear nerve (8th cranial nerve) is the primary nerve that, when irritated, can lead to tinnitus or ringing in the ears. 1, 2, 3 This sensory nerve consists of two components: the cochlear nerve responsible for hearing and the vestibular nerve responsible for balance.

Mechanism of Tinnitus from CN VIII Irritation

• The vestibulocochlear nerve transmits auditory information from the inner ear to the brain stem and ultimately to the auditory cortex 1
• When this nerve is irritated or compressed, it can result in abnormal neural activity that the brain interprets as sound (tinnitus) even when no external sound is present 4
• Common causes of vestibulocochlear nerve irritation include:
  • Neurovascular compression by vascular loops in contact with CN VIII 5
  • Vestibular schwannomas (acoustic neuromas) 5
  • Meningiomas affecting the cerebellopontine angle 5
  • Endolymphatic sac tumors 5

Types of Tinnitus Related to CN VIII

1. Subjective Nonpulsatile Tinnitus

   • Most common form, described as ringing, buzzing, or clicking sensations 5
   • Often associated with sensorineural hearing loss 6
   • May be unilateral (one ear) or bilateral (both ears) 5

2. Typewriter Tinnitus

   • Characterized by paroxysmal attacks of staccato sounds
   • Specifically caused by neurovascular compression of the cochlear nerve
   • Responds well to carbamazepine treatment 5

Diagnostic Approach for CN VIII-Related Tinnitus

Clinical Evaluation

• Determine if tinnitus is:
  • Pulsatile vs. nonpulsatile
  • Unilateral vs. bilateral
  • Associated with hearing loss or neurological symptoms 7

Imaging Studies

• MRI of internal auditory canals with contrast: Gold standard for evaluating CN VIII and detecting vestibular schwannomas 5
• Heavily T2-weighted MRI sequences: Best for visualizing neurovascular compression of CN VIII 5
• MR angiography: Helpful for evaluating vascular loops that may compress CN VIII 5

Special Considerations

• Patients with tinnitus are 80 times more likely to have vascular loops in contact with CN VIII than those without tinnitus 5
• Unilateral tinnitus, especially when accompanied by asymmetric hearing loss, warrants MRI to rule out vestibular schwannoma 7, 6

Management of CN VIII-Related Tinnitus

Medical Management

• For typewriter tinnitus (neurovascular compression): Carbamazepine 5
• For tinnitus associated with sudden sensorineural hearing loss: Corticosteroids within 2 weeks of symptom onset 5
• Cognitive behavioral therapy: Only treatment shown to improve quality of life in patients with chronic tinnitus 7, 6

Surgical Management

• Reserved for cases with identifiable structural causes:
  • Microvascular decompression for severe neurovascular compression
  • Tumor resection for vestibular schwannomas or other masses

Important Caveats and Pitfalls

• Vascular loops in contact with CN VIII are common (present in up to one-third of normal patients) and may be an incidental finding 5
• Not all patients with hearing loss develop tinnitus; age-related changes in inhibitory circuits may be protective in some individuals 4
• Avoid unnecessary imaging for non-concerning tinnitus presentations (bilateral, non-pulsatile, without hearing loss) 7
• Never delay referral for unilateral tinnitus, which may indicate a potentially serious underlying condition 7
• Hidden hearing loss from cochlear synaptopathy may cause tinnitus even with normal audiometric thresholds 5

Remember that while the vestibulocochlear nerve is the primary nerve involved in tinnitus, other factors including central auditory processing changes and cross-modal compensations in subcortical structures may contribute to the perception of tinnitus 4.