FACIAL NERVE INJURY

Dr Shalina KaurENT HRPZ

• The facial nerve is 7th of 12 paired cranial nerves, it’s a mixed nerve with motor and sensory roots.

• Emerges from brain stem between pons and the medulla, controls the muscle of facial expression

• It functions in the conveyance of taste sensations from the anterior two thirds of the tongue and oral cavity

• It also supplies preganglionic parasympathetic fibre to several head and neck ganglia

Facial nerve origin

Facial Nerve Components– Motor

• Supplies muscles of facial expression• Stylohyoid muscle• Posterior belly of digastric• Stapedius muscle

– Sensory• Taste to anterior 2/3 of the tongue• Sensation to part of the TM, the wall of the EAC, postauricular skin, and

concha

– Parasympathetic• Supplies secretory control to lacrimal gland and some of the

seromucinous glands of the nasal and oral cavities• Chorda tympani carries parasympathetics to the submandibular and

sublingual glands

Nuclei of the facial nerve• Motor nucleus: in the Pons fibers from it will surround the

abducent nerve nucleus to form the facial colliculus.• Nucleus solitarious: in the medulla oblongata and

receives the taste fibers• Superior salivatory nucleus: in the Pons and gives rise

to the parasympathetic fibers

Motor root of 7th nerve

6th nerve nucleus

Motor nucleus of 7th n

Sup. salivary nuceus

Tractus solitariusNervus Intermedius

Internal Auditory Meatus

Geniculate GanglionOval Window

Nerve to stapedius

Chorda Tympani

Stylomastoid Foramen

Lacrimal Gland

Sphenopalatine Ganglion

Greater Superficial Petrosal Nerve

Sublingual Gland

Submandibular GlandTemporal MB

Zygomatic MBBuccal MB

Mandibular MBCervical MB

From pons to internal acoustic meatus

The nerve passes laterally with the vestibulocochlear nerve (CN VIII) to the internal auditary meatus. At the bottom of the meatus the nerve enters the facial bony canal where it runs laterally above the vestibule of inner ear.

Reaching the medial wall of the middle ear, it bends sharply backwards above the promontory (forming its genu) where the genicular ganglion is found

It then arches downwards in the medial wall of the middle ear to reach the stylomastoid foramen.

INTRACANIAL SEGMENTS

Facial Nerve AnatomyINTRACRANIAL SEGMENT:•from the brainstem to the internal auditory canal•15-17 mm

two components: 1. Facial nerve proper (motor):•arising from facial motor nucleus in pons.

2- Nervus intermedius:

•it is the sensory root of facial lies position between the facial proper and vestibulcochlear nerve in the pontocerebellar angle.

•Carrying para-sympathetic fibers (from superior salivary nucleus) and taste fibers ( to the solitary nucleus ) Both join at the CPA/IAC to form the common facial nerve

1. MEATAL 8-10mm– Portion of the facial nerve traveling to the meatal foramen of IAC– Travels in the anterior superior portion of the IAC (7-UP, 8-Down)

»Posterior superior – superior vestibular nerve»Posterior inferior – inferior vestibular nerve»Anterior inferior – cochlear nerve

INTRATEMPORAL SEGMENTS

IAC and bill’s bar

Facial nerve in IAC

VII facial nerveNI nervus intermediusVIIIC cochlear nerveVIIIvs superior vestibular nerveVIIIvi inferior vestiblar nerve

INTRATEMPORAL SEGMENTS

2. Labyrinthine 4mm–From fundus to the geniculate ganglion–Runs in the narrowest portion of the IAC (0.68mm in

diameter)–Greater superficial petrosal nerve comes off at this point

3. Tympanic11mm–Runs from geniculate ganglion to the second genu–It lies above oval window and below lateral SCC

4. Mastoid 13 mm–From second genu to stylomastoid foramen–Gives off branches to the stapedius muscle and the chorda

tympani

EXTRA TEMPORAL SEGMENT• exits stylomastoid foramen

– Postauricular nerve - external auricular and occipitofrontalis muscles

– Branches to the posterior belly of the digastric and stylohyoid muscles

EXTRA TEMPORAL SEGMENT• Enters parotid gland splitting it into a superficial and

deep lobe• Pes Anserinus

– Branching point of the extratemporal segments in the parotid– To Zanzibar By Motor Car

» Temporal» Zygomatic» Buccal» Marginal mandibular» Cervical

NERVE INJURY:CLASSIFICATION

Components of a Nerve• Endonerium

– Surrounds each nerve fiber– Provides endoneural tube for regeneration– Much poorer prognosis if disrupted

• Perinerium– Surrounds a group of nerve fibers– Provides tensile strength– Protects nerve from infection– Pressure regulation

• Epinerium– Surrounds the entire nerve– Provides nutrition to nerve

Sunderland Nerve Injury Classification

Sunderland Nerve Injury Classification

–Class I (Neuropraxia)• Conduction block caused by cessation of axoplasmic flow• What one experiences when their leg “falls asleep”• Full recovery

–Class II (Axonotmesis)• Axons are disrupted• Wallerian degeneration occurs distal to the site of injury• Endoneural tube still intact• Full recovery expected

–Class III (Neurotmesis)• Neural tube is disrupted• Poor prognosis• If regeneration occurs, high incidence of synkinesis (abnormal

mass movement of muscles which do not normally contract together)

Sunderland Nerve Injury Classification• Class IV

• Epineurium remains intact• Perineurium, endoneurium, and axon disrupted

• Poor functional outcome with higher risk for synkinesis

• Class V• Complete disruption• Little chance of regeneration• Risk of neuroma formation

BELL’S PALSY• Temporary facial paralysis caused by damage to the 7 th

cranial nerve (facial nerve)• Inflamation that causes pressure on the Facial Nerve,

which effect the Facial Muscles.• Usually only one side of the face is affected and you have

trouble closing your eye and producing tears, controlling drooling and movement of the mouth

FACIAL NERVE TRAUMA

- Second most common cause of FN paralysis behind Bell’s Palsy

- Represents 15% of all cases of FN paralysis

- Most common cause of traumatic facial nerve injury is temporal bone fracture

Temporal Bone Fracture– 5% of trauma patients sustain a temporal bone fracture

– Three types (Ulrich 1926 classification)» Longitudinal

• Most common type – 70-80%• Fracture line parallel to long axis of petrous pyramid• Secondary to temporoparietal blunt force• EAC and TM laceration• Results in facial nerve paralysis in 15-20% of cases» Transverse

• 10-20% of fractures• Fracture line perpendicular to long axis of petrous pyramid• Secondary to frontal or occipital blow, intact EAC• Results in facial nerve paralysis in 50% of cases» Mixed

• 10% of temporal bone fractures

Longitudinal fracture Transverse fracture1. Bleeding from external canal due

to laceration of skin and ear drum2. Fractures involving the bony

portion of external canal3. Ossicular chain disruption causing

conductive deafness.4. Facial palsy (rare) 20% usually at

the level of horizontal segment distal to geniculate ganglion

5. CSF otorrhoea (usually temporary)6. Sensorineural hearing loss can

occur due to consussion

1. Sensorineural hearing loss due to damage to 8th cranial nerve

2. Haemotympanum (conductive deafness)

3. Facial palsy due to damage of facial nerve

4. Vertigo

5. Labyrinthitis ossificans (this should be borne in mind before performing cochlear implant in these pts)

Penetrating Trauma-Typically results in FN injury in the extratemporal segments

-Gun shot wounds cause both intratemporal and extratemporal injuries• GS wounds to temporal bone result in FN paralysis in 50% of cases

• Mixture of avulsion and blunt trauma to different portions of the nerve

• Much worse outcome when comparing GS related paralysis to TB fracture related paralysis

Iatrogenic Facial nerve Trauma–Surgical

• Most common is parotidectomy• Most common otologic procedures with FN paralysis:

– Mastoidectomy – 55% – Tympanoplasty – 14%– Exostoses removal – 14%– Mechanism : direct mechanical injury or heat generated from

drilling– Most common area of injury - tympanic portion due to its high

incidence of dehiscence in the this area, and its relation to the surgical field

• Unrecognized injury during surgery in nearly 80% of cases–Birth trauma

• Forceps delivery with compression of the facial nerve against the spine

Work-up: History• History

• Mechanism – recent surgery, facial/head trauma

• Timing – progressive loss of function or sudden loss• Transected nerve -> sudden loss • Intraneural hematoma or impengiment -> progressive loss (better prognosis)

• Associated symptoms – hearing loss ,vertigo

Work-up: Physical• Physical Examination

– full head and neck examination– Facial asymmetry– Signs of facial injury: lacerations, hematomas, bruising– Exam head/scalp for signs of injury to help guide you to

vector of force if head trauma is involved– Otoscopic examination is a must

• Canal lacerations or step-offs deformity• Hemotympanum, TM perforation, drainage of blood or

clear fluid from middle ear• Tuning fork tests help to determine any hearing loss

Clinical facial nerve test

• Facial movement:• Temporal branches:

• Wrinkle forehead• Elevate eyebrow

• Zygomatic branches:• Close the eyes

• Mandibular branches:• Show teeth• Blow cheek• Cervical grimacing

House-Brackmann Grading SystemGrade Characteristics

I. Normal facial function in all areasII. Mild dysfunction •Slight weakness noticeable on close inspection

•Forehead - Moderate-to-good function•Eye - Complete closure with minimal effort•Mouth - Slight asymmetry

III. Moderate dysfunction-First time you can notice a difference at rest

•Obvious but not disfiguring difference between the two sides• Forehead - Slight-to-moderate movement•Eye - Complete closure with maximum effort•Mouth - Slightly weak with maximum effort

IV. Moderately severe dysfunction-First time you have incomplete eye closure-No forehead movement

•Obvious weakness and/or disfiguring asymmetry• Forehead – No motion

•Eye - Incomplete closure

•Mouth - Asymmetric with maximum effort

V. Severe dysfunction •Only barely perceptible motion•At rest, asymmetry •Forehead – No movement•Eye - Incomplete closure•Mouth - Slight movement

VI. Total paralysis No movement

Work-up: Radiologic Tests

• HRCT scans• Bony evaluation • Locate middle ear, mastoid, and temporal bone pathology

• Gadolinium enhanced MRI• Rarely done in traumatic facial nerve injury• better visualisation of soft tissue condition

Facial Nerve Testing• to assess the degree of electrical dysfunction• Can pinpoint the site of injury• Helps determine treatment• Can predict recovery of function – partial paralysis is a much better prognosis than total paralysis

• two categories:–Topographic test–Electrodiagnostic test

Facial Nerve TestingTopographic test•Tests function of specific facial nerve branches

•Determine the site of facial nerve injury

•Do not predict potential recovery of function

• Schimer’s test• Stapedial reflex• Taste test• Submandibular salivary flow test

Topographic test• Lesion at nucleus in pons :

• Only motor fx affected• No taste,lachrymation salivation

disturbance• no loss of stapedial reflex

• Lesion in CPA/IAM/labyrinthine segment:• Impaired lachrymation, stapedial

reflex , taste and salivation• Lesion between geniculate ganglion

and nerve to stapedius:• Intact lachrymation• Impaired stapedial reflex and taste

Topographic test• Lesion between the nerve to stapedius and chorda tympani:• Intact lachrymation and stapedial reflex

• Impaired taste• Lesion below level of chorda tympani:• Pure motor deficit• Intact lachrymation, stapedial reflex, salivation and taste

Schimer’s test

• The eye is gently dried of excess tears or topical LA• The filter paper is folded 5 mm from one end • The folded tip is inserted into the lower lid – at the junction

of the middle and outer thirds of the lower lid – taking care not to touch the cornea or lashes.

• The patient is asked to keep their eyes closed for the duration of the test.

• After 5 minutes, the filter paper is removed and the amount of wetting from the fold is measured.

Schimer’s test• GENERAL INTERPRETATION:

• Normal which is ≥15 mm wetting of the paper after 5 minutes.

• Mild which is 14-9 mm wetting of the paper after 5 minutes.

• Moderate which is 8-4 mm wetting of the paper after 5 minutes.

• Severe which is <4 mm wetting of the paper after 5 minutes.

• Normal test suggest lesion after geniculate body• In facial nerve trauma: compare with normal side, reduction of >25% is significant(positive schimmer test)

Stapedial reflex

• Part of audiometric evaluation for all patient with facial nerve weakness

• Accomplished at the time of impedance testing

Stapedial reflex• Loud sound directed to either ear cause bilateral contraction of the stapedius muscle• Normally 75-95db above the threshold• Provide diagnostic information of cochlear, retrocochlear and brainstem pathology

ME(middle ear) IE(Inner ear), VIII(Vestibular Cochlea nerve), CN(cochlear nucleus) SOC (superior olivary complex ) VII facial nerve

• Both ipsilateral and contralateral are measured• Normal ipsilateral: intact intergrity of reflex arch of the

tested ear• Normal contralateral: implies intact afferent and brainstem

pathway of tested ear and intact efferent of contralateral ear.

• In VII n palsy:• Absent :the site of injury most likely between geniculate

ganglion and nerve to stapedius• Present; injury site is distal to nerve to stapedius.

Right VII n pathology

Cochlear pathology

Vestibulocochlear nerve pathology

Severe middle ear pathology

Brainstem pathology

Testing taste• sweet, salt, sour and bitter taste are tested along the lateral margin

of anterior 2/3 toward tip oftongue.• Patient must not retract the tongue in• Electrogustometry:

• Electrical method• Small current applied to lateral border of anterior 2/3 of tongue• Current slowlt increase until patient able to perceive the metallic

taste • Normal threshold: 1 mA• 4 mA in chorda tympani involvement

Submandibular gland flow

Sialometry•Under LA: small polythene tube passed into Wharton’s duct•Salivation induced by stimulus of 6% citric acid on the anterior tongue.•Drops of saliva from each side is mesured and compared

Electrodiagnostic test• Utilize electrical stimulation to assess nerve conductivity/function

• Most commonly used today• Able to demonstrate evidence of degeneration as early as 3 days after onset

• Common tests:• Nerve excitabillity test• Maximal stimulation• Electroneuronography• electromyography

Nerve Excitability Test (NET) Compares amount of current required to illicit minimal muscle contraction - normal side vs. paralyzed side•How it is performed:

• A stimulating electrode is applied over the stylomastoid foramen

• DC current is applied percutaneously• Face monitored for movement • The electrode is then repositioned to the

opposite side, and the test is performed again•A difference of 3.5 mA or greater between the two sides is considered significant•Drawback - relies on a visual end point (subjective)

Maximal Stimulation Test (MST)• Similar to the NET, except it utilizes maximal stimulation

rather than minimal• Usually >5 mA• The paralyzed side is compared to the contralateral side• Not accurate if done within 72 hours• Comparison rated as equal, slightly decreased,

markedly decreased, or absent– Equal or slightly decreased response = favorable for complete

recovery– Markedly decreased or absent response = advanced

degeneration with a poor prognosis• Drawback – Subjective

Electroneurography (ENoG)• Considered the most accurate of the electrodiagnostic tests• How it works:

• Bipolar electrodes deliver an impulse to the FN at the stylomastoid foramen

• Summation potential is recorded by another device placed at nasolabial region

Electroneurography (ENoG)• Stimulus gradually increased until there is no further increase in the

respond amplitude • The peak to peak respond amplitude is proportional to number of

intact axons• The two sides are compared as a percentage of response

Electroneurography (ENoG)• 90% degeneration – surgical decompression should be

performed• Less than 90% degeneration within 3 weeks predicts 80 -

100% spontaneous recovery• Disadvantages: discomfort, cost, and test-retest variability

Electromyography• Determines the activity of the muscle itself

• How it works–Needle electrode is inserted into the muscle, and recordings

are made during rest and voluntary contraction• Normal = biphasic or triphasic potentials• Demonstrate the signs of recovery• 10-21 days post injury - fibrillations• 6-12 weeks prior to clinical return of facial function –

polyphasic potentials are recordable• Does not require comparison with normal side• Not helpful of recent onset injury:• Showed denervation potential only after 8-10 days

FACIAL NERVE TRAUMA:Surgery

General surgical guideline• Reconstruction:• When decided for surgery:• informed consent and preoperative consult are important• Must inform:

• patient’s face will never be symmetrical or have a normal balance

General surgical guideline

General surgical guideline•Blunt Trauma• Birth trauma and Extratemporal blunt trauma

– Recommend no surgical exploration– >90% expected to regain normal/near normal recovery

• Complete paralysis following temporal bone fracture– Likely nerve transection– Immediate surgical exploration– 30% need nerve repair

• Partial or delayed loss of function– Approach similar to iatrogenic partial or delayed loss– High dose steroids– ENoG 72 hours

• >90% degeneration – explore• < 90% degeneration – can monitor and explore at later date

depending on worsening or failure to regenerate

Surgery for acute facial nerve trauma•Facial nerve decompression:• Localise site of injury pre operatively

• Full exposure of the nerve from IAC to the stylomastoid foramen if can’t localize

• Approach:• Intact - Transmastoid/Middle cranial fossa approach• Absent – Transmastoid/Translabyrinthine approach

• Diamond burs and copious irrigation is utilized to prevent thermal injury

• Thin layer of bone overlying the nerve is bluntly removed• Remove bone fragments and hematoma neurolysis or not to

open the nerve sheath is debatable – Recommended to drain hematoma if identified

Acute vs. Late Decompression - Controversial

• Quaranta et al (2001) examined results of 9 patients undergoing late nerve decompression (27-90 days post injury) who all had >90% degeneration– 7 patients achieved HB grade 1-2 after 1 year– 2 achieved HB grade 3– Concluded that patients may still have a benefit of

decompression up to 3 months out• Shapira et all (2006) performed a retrospective review looking

at 33 patients who underwent nerve decompression. They found no significant difference in overall results between those undergoing early (<30 days post-injury) vs. late (>30 days post-injury) decompression

• Most studies like these have been very small, and lack control groups.

Facial Nerve Repair • Recovery of function begins around 4-6 months and can last up

to 2 years following repair• Nerve regrowth occurs at 1mm/day• Goal is tension free and healthy anastomosis• 2 weeks following injury -> collagen and scar tissue replace

axons and myelin– Nerve endings must be excised prior to anastomosis

• Rule is to repair earlier than later - controversial– After 12-18 months, muscle reinnervation becomes less efficient even

with good neural anastomosis – Some authors have reported improvement with repairs as far out as

18-36 months– May and Bienstock recommend repair within 30 days, but other

authors have found superior results if done up to 12 months out

Primary Anastomosis• Best overall results of any surgical

intervention• Done if defect is less than < 2cm

– Mobilization of the nerve can give nearly 2cm of length

– With more mobilization comes devascularization• Endoneurial segments must match -

promotes regeneration• Ends should be sutured together using

three to four 9-0 or 10-0 monofilament sutures to bring the epineurium or perineurium together

Grafting and Nerve Transfer• Performed for defects > 2cm• Approach is based on availability of proximal nerve ending

• Success of a nerve graft depends on the following factors:• The number of axons remaining in the nerve• The potential for regeneration of axons• The status of the facial muscles

• Results in partial or complete loss of donor nerve function

• Great auricular nerve– Commonly used, usually in surgical field– Located within an incision made from the mastoid tip to the

angle of the mandible– Can only harvest 7-10cm of this nerve– Loss of sensation to lower auricle with use

• Sural nerve– Located 1 cm posterior to the lateral malleolus– Can provide 35cm of length– Very useful in cross facial anastomosis– Loss of sensation to lateral calf and foot

• Ansa Cervicalis – only utilized if neck dissection has been performed

• 92-95% of these patients have some return of facial function– 72-75% have good results (HB 3 or above)

THANK YOU