25th June 2023

Vestibulocochlear Nerve and Spinal Accessory Nerve – VIII, XI

CN VIII – Vestibulocochlear nerve

The vestibulocochlear nerve arises from the inner ear apparatus for hearing and equilibrium, passing through the internal acoustic meatus. It has two divisions:

• The cochlear division – for hearing
• The vestibular division – for balance

Labyrinthitis and vestibular neuritis

Vestibular neuritis occurs when only the vestibular division of the vestibulocochlear nerve is inflamed, resulting in continuous dizziness and vertigo but no change in hearing. There is also an association with viral infections, usually upper respiratory tract infections.

Labyrinthitis occurs when both the cochlear and vestibular divisions of the nerve are affected, resulting in hearing changes in addition to continuous dizziness and vertigo. There is also an association with upper respiratory tract infections as with vestibular neuritis. Treatment for vestibular neuritis and labyrinthitis is with antihistamines like betahistine and meclizine.

It should be noted that Ménière’s disease with its presentation of vertigo, tinnitus and hearing loss is a disorder of the inner ear rather than of the vestibulocochlear nerve itself. The difference is that symptoms of Ménière’s disease are chronic and episodic, and there is no association with infection.

Vestibular schwannoma (acoustic neuroma)

As covered earlier in the section, a vestibular schwannoma (or acoustic neuroma) is a benign tumour of the vestibulocochlear nerve (CN 8) that can also affect the facial nerve (CN 7).

CN XI – Spinal accessory nerve

The spinal accessory nerve is formed from a cranial root from the medulla and a spinal root from the superior spinal cord which passes into the cranium via the foramen magnum. The combined accessory nerve leaves the cranium via the jugular foramen. The spinal accessory nerve supplies motor fibres to the larynx, pharynx, and soft palate, and innervates the sternocleidomastoid and the trapezius muscles.

Disorder of CN XI manifests primarily as weakness of the trapezius and sternocleidomastoid with signs of:

• Asymmetric neckline
• Drooping shoulder ipsilaterally
• Winged scapula
• Weakness of elevation of the shoulder ipsilaterally
• Weakness of head turning to the contralateral side – this is because the ipsilateral sternocleidomastoid muscle, which functions to push the head to the contralateral side, is affected

The aetiology is primarily due to trauma and more commonly iatrogenic trauma, e.g. neck surgery, lymph node biopsy.