Facial nerve Flashcards
Where does the facial nerve (CN7) originate from within the brain?
Lateral surface of the brainstem between the pons and medulla
Through what does the facial nerve pass out out of the cranial cavity?
Internal acoustic meatus
Describe the course of the facial canal once it enters the internal acoustic meatus?
It follows the facial canal (which is within the petrous part of the temporal bone)
It gives off branches along its course and exits the skull at
the stylomastoid foramen
What branches are given off the facial nerve within the facial canal?
1) The greater petrosal nerve
2) Nerve to stapedius muscle
3) Chorda tympani nerve
Describe the course of the facial nerve after exiting the stylomastoid foramen (include the branches)
Gives off the posterior auricular nerve (innervates skin behind ear)
It then splits within the parotid into:
To - temporal Zanzibar - zygomatic By - Buccal Motor - marginal Car - cervical
How do you test the 5 branches of the facial nerve?
To - temporal - Raise eyebrows Zanzibar - zygomatic - Scrunch up eyes By - Buccal - Puff out checks Motor - marginal - clench teeth Car - cervical - tense neck
What is thought to be the cause of Bell’s palsy?
A viral infection of the 7th (facial) nerve
causing swelling of the nerve in the tight facial canal
What % of facial palsies are thought to be due to Bell’s palsy?
80%
Describe the onset of Bell’s palsy?
Sudden onset
Preceded by URTI
What are Tavener’s criteria?
(A way to diagnose Bell’s palsy)
Acute onset
Complete hemifacial palsy (as LMN)
No CNS pathology
No ear pathology
How is Bell’s palsy diagnosed?
It’s a diagnosis of exclusion
What is the treatment for Bell’s palsy?
If within 48 hrs then treat with:
High dose oral steroids
What is the prognosis for Bells palsy?
most resolve
some left with residual weakness
How long before recovery starts with Bell’s palsy?
Usually begins with 2 months
What are the most common tumours of the parotid?
BENIGN pleomorphic adenomas
How can masses in the parotid affect the facial nerve?
It can take out 1, 2, 3, 4 or all 5 of the branches depending on size and location.
Weakness may occur initially
and lead to complete palsy
What part of the skull does the facial nerve run across?
the posterior cranial fossa
Where is a common site of skull base pathology that affects CN 7?
the cerebellopontine angle (CPA)
If a facial nerve palsy was associated with unilateral hearing loss and tinnitus what would you suspect and why?
That there was a mass at the cerebellopontine angle (CPA)
as CN8 (vestibulocochlear) also passes along here with CN7
What type of fractures can affect the facial nerve and what is also commonly associated with this and why?
Transverse skull fractures (15% affect CN7)
hearing loss and tinnitus are common due to CN8 (vestibulocochlear) involvement
Nerves 9-12 may be affected.
What differentiates a lower vs an upper motor neurone lesion of CN 7?
If upper motor neurone
the palsy will be contralateral
There will be forehead muscle sparingas each facial nerve supplies both sides
If LMN it is ipsilateral and complete paralysis
What is Ramsay Hunt syndrome?
shingles causing:
facial palsy and pain
vesicles on ear drum, canal and pinna
What are the adverse outcomes of Ramsay Hunt syndrome?
Deafness
vertigo
as palsy is severe pt may not recover
What is the treatment for Ramsay Hunt syndrome?
acyclovir
What is the treatment/management for facial palsy?
Treat underlying cause
Eye drops as unable to create tear film leading to conjunctival ulceration and blindness
What is the job of the greater petrosal nerve?
To stimulates the (parasympathetic) secretormotor activity in the lacrimal gland
Convey taste from the palate
What is the job of the stapedius muscle
To stabilise the stapes
What is the job of the chorda tympani nerve?
provides taste to anterior 2/3rds of tongue
Where is the motor nucleus of the facial nerve located?
In the pons
What is the counterintuitive way that deep lobe of parotid tumours can present?
Oropharyngeal mass which displaces tonsils medially
What are the peripheral causes of facial nerve palsy?
Trauma (e.g. forceps delivery or penetrating injury)
Iatrogenic (e.g. parotid or submandibular (mannibular nerve) nerve damage from sugery)
Malignant parotid tumours
Inflammatory conditions of the parotid (e.g. sarcoidosis)
What are the middle ear causes of facial nerve palsy?
Iatrogenic (mastoid and middle ear surgery MUST warn pts of this)
Infection (cholesteatoma, AOM, mastoiditis, herpes zoster)
Tumours
What are the signs of cholesteatoma?
A MEDICAL EMERGANCY!
Discharging ear and a facial palsy
What is the treatment for cholesteatoma?
antibiotics
Surgical exploration and excision of cholestiatoma
What is the treatment of acute otitis media (AOM)?
antibiotics
and often a myringotomy (tiny incision is created in the eardrum) to drain pus
What are the petrous temporal bone causes of facial nerve palsy?
Trauma (transverse fractures of the skull)
Tumours
What are the intracranial bone causes of facial nerve palsy?
Tumour (e.g. acoustic neuromas, facial nerve neuromas, meningioma)
Iatrogenic (skull base surgery)
Vascular (stroke)
Neurological (e.g. multiple sclerosis)
What are the side variable causes of facial nerve palsy?
Bells palsy (lower nerve palsy)
Ramsay-Hunt syndrome
Guillian-Barre syndrome
