PBL4

Question 1

what nerves is the facial nerve made out of

Answer 1

Sensory, motor and autonomic (parasympathetic) fibres

Question 2

where does the facial nerve emerge

Answer 2

Emerges from the ponto-medullary junction (4 in the pons)

Question 3

what are the two divisions of the facial nerve

Answer 3

A large motor root

Smaller sensory nerve (for taste) and pre-ganglionic parasympathetic fibres

Question 4

what is the course of the facial nerve

Answer 4

CN VII exits the posterior cranial fossa through the internal auditory meatus (along with cranial nerve VIII).

Courses through the temporal bone close to the tympanic cavity

While coursing through the temporal bone, the facial nerve gives rise to proximal branches:

• Greater petrosal nerve (pre-ganglionic parasympathetic motor innervation to lacrimal gland),
• a nerve to the stapedius muscle (motor nerve that dampens vibrations of the stapes)
• the chorda tympani nerve which contains sensory taste afferents originating from the taste buds of the anterior 2/3 tongue.

The facial motor nerve then exits the temporal bone through the stylomastoid foramen.

The nerve then enters the parotid gland and gives rise to the terminal branches (temporal, zygomatic, buccal, mandibular and cervical).

Question 5

what is the motor function of the facial nerve

Answer 5

• muscles of facial expression

- Facial motor nucleus in the caudal portion of the ventrolateral pontine tegmentum

Question 6

what is the sensory and special sensory fo the facial nerve

Answer 6

Sensory and special sensory (taste) to anterior ⅔ tongue

- Originate in the nucleus solitarius, join the facial nerve at the geniculate ganglion

Question 7

what is the parasympathetic to the facial nerve

Answer 7

Parasympathetic to submandibular and sublingual salivary glands, nasal glands, lacrimal gland
- Originating from superior salivatory nucleus at pontine tegmentum join sensory branch.

Question 8

what happens to the facial nerve after it exits stylomastoid foramen

Answer 8

After facial nerve exits stylomastoid foramen, passes over parotid gland before dividing in to terminal motor branches

Question 9

what are the motor terminals to the muscle of facial expression

Answer 9

Temporal
Zygomatic
Buccal
Mandibular (Marginal)
Cervical

Question 10

describe bells palsy

Answer 10

Sudden onset of facial muscle weakness/paralysis in all facial nerve innervated muscles
Often unilateral
Onset over few hours

Question 11

what causes belly palsy

Answer 11

Due to compression at SM foramen causing inflammation/damage to the extracranial component of the facial nerve = MOTOR FUNCTION AFFECTED

Question 12

what are the symptoms of bells palsy

Answer 12

Drooping face on one side-facial muscle weakness

Can’t close eyelids-obicularis oculi

Drooling from one side of mouth

Chewing affected

Cant whistle, wink, blow bubbles

Speech impaired-facial muscles help form sounds e.g ‘p’

Hyperacuisis-paralysis of stapedius muscle in middle ear.

Earrache or pain underneath ear on affected side

Dry irritated eyes-can’t blink, maybe reduced secretions

Dryness of mouth

Taste sensation may be affected

Question 13

why is there not forehead sparing in bells palsy

Answer 13

This is because the lower motor neuron axons of the facial nerve are affected.

Question 14

what causes forehead sparing

Answer 14

Forehead sparing if upper motor neuron (UMN) involvement as the forehead muscles receive bilateral cortical input from UMNs
- Damage to the UMNs on one side would therefore not produce paralysis of these muscles because of input from the other side.

Question 15

what does a damage brainstem lower motor neurones cause

Answer 15

ipsilateral weakness of lower and upper face

- no forehead sparing

Question 16

what does a damage to a motor cortex to upper motor neurone do to

Answer 16

• contralateral weakness of lower face do

- forehead spared due to bilateral innervation

Question 17

what is the treatment for bells palsy

Answer 17

• Steroids-prednisolone for 10 days
• Eye tape
• Eye drops
• 75% recover by 2-3 months as axons regenerate
• Some are left with a degree of permanent weakness

Question 18

explain the signs and symptoms 10 years later

Answer 18

Acoustic neuroma/vestibulo-schwannoma
- Slow growing benign schwann cell tumour of vestibular portion of CNVIII

Initial sx are unilateral deafness and tinnitus

Balance and vertigo, 3rd commonest sx

If large, protrudes out of auditory canal into posterior cranial fossa at cerebellopontine angle

• Compression of proximal CN VII as it leaves pons
• Taste sensation, facial weakness, drooping

CN V- facial numbness and tingling

Question 19

what are the treatments for 5 years later

Answer 19

Audiometry test

MRI imaging shows a tumour that looks pear shaped invading the posterior fossa.

Surgery or radiotherapy to shrink the tumour

Radiotherapy:

• Noninvasive
• Localised preventing surrounding damage
• Growth arrest or tumour killing, shrink but don’t disappear
• Can continue to grow, 20%-follow-up to check for this

Surgery can be curative
For preservation of the facial nerve as deafness likely to be permananent