19. facial nerve anatomy and its disorders

8/2/2019 19. Facial Nerve Anatomy and Its Disorders

1/69

Presenter : Dr. Neha Goel

Moderator : Dr. Arjun Dass


2/69

Embryonic Development :

Facial nerve course,branching pattern, andanatomical relationships areestablished during the first 3months of prenatal life

The nerve is not fullydeveloped until about 4 yearsof age

The first identifiable facialnerve tissue is seen at thethird week of gestation-facioacoustic primordium or

crest


3/69

S

Chorda tympani is the first branch to appear.


4/69

Applied Anatomy :Facial nerve lies just beneath the skin near the mastoid tip at birth

and is vulnerable to post auricular skin incision. As the mastoid tip

forms and elongates, facial nerve assumes its more medial and

protected position

Individual axons of facial nerve also undergo myelination until the

age of 4 years, an important consideration during electrical testing of

facial nerve at this age

Facial nerve develops within second brachial arch during the time

that closely adjacent external and middle ear region. Anomalies of

facial nerve should be anticipated whenever there is an associated

malformation of external or middle ear


5/69

Facial Nerve :Facial nerve is a mixed nerve

Motor root : muscles of 2ndbrachial arch.

Sensory root nerve ofWrisberg carries taste fibers

from the anterior 2/3 of thetongue and general sensationfrom the concha andretroauricular skin.

Also it carries secretomotorfibers to the lacrimal,submandibular and sublingualglands as well as those in thenose and palate.


6/69


7/69

Overview of Facial Nerve

anatomy in the skull

Lacerate foramen

Facial

canal

Internal

Acoustic

Meatus

Stylomastoid

Foramen

Hiatus of canal of greater

superficial petrosal nerve

Pterygoid

canalGreater

superficial

Petrosal

nerve

(GSPN)

Petrotympanic

fissure

Greater and

lesser palatine

canals

Chorda tympani nerve

Facialnerve

Facialnerve

Posterior

Cranial

Fossa (PCF)

Inferior Orbital Fissure

Posterior

auricular N.


8/69

Supranuclear Part :Primary somatomotor cortex : precentral gyrus (area

4,6,8) internat capsule via cortico bulbar tractpyramidal tracts pons

In basal pons most of the facial nerve fibres cross themidbrain to reach the contralateral facial nerve nucleus

Some fibres innervate ipsilateral facial nerve nucleus,majority of which are destined for temporal branch

Extrapyramidal cortical input from hypothalamus, globuspallidus and frontal lobe -involuntary facial expressions

with emotionsVisual system : blink reflex

Trigeminal nerve : corneal reflex

Auditory nuclie : response to loud sound


9/69

Applied Anatomy

Central nervous system lesion spare forehead musclesince they receive input from both cerebral cortices,

whereas peripheral lesions involve all branches of facial

nerve


10/69

Facial Nucleus and Brainstem:

Facial nerve originates from facial

motor nucleus which lies in lateral

portion of pons. Facial nerve

hooks around the nucleus of sixthnerve.

Facial nerve exits the brainstem at

pontomedullary junction caudal tofifth nerve and 1.5mm anterior,

medial and superior to eighth

cranial nerve.


11/69


12/69

Cerebello pontine Angle

Facial nerve leaves brainstem atpontomedullary junction , lies in

close relation to vestibulocochlear

nerve and nerve of wriseburg

Trigeminal nerve lies superiorly and

cranial nerve IX X XI XII lie

inferiorly


13/69

Applied Anatomy :

Vestibular schwanomma in CPA

jeopardises facial nerve during

its growth and attempted

surgical removal due to intimate

relation.

In CPA, facial nerve is covered

with pia, is placed in CSF, and is

devoid of epineurium, leaving it

susceptible to manipulationtrauma during intracranial

surgery


14/69

Meatal Part :

Facial nerve passes through the

porus of IAC.

Superior and inferior vestibular

nerves lie posterior andinferoposterior to facial nerve in

IAC. Cochlear nerve lies caudal to

facial nerve.

The length of IAC portion of nerve

is around 8-10mm.


15/69

Fallopian Canal :

Subsequently fallopian canal

takes a long tortuos course

through temporal bone ~ 30 mm

It provides a bony covering for

facial nerve longer than that of any

other nerve

Protects the facial nerve but alsorenders it vulnerable to certain

diseases and disorders


16/69

Labyrinthine Segment :

Facial nerve enters the labyrinthinesegment of facial nerve through the

meatal foramen

the narrowest (0.68 mm in diameter )

and lined by fibrous annular ligamentthe shortest portion of the canal. (4

mm in length)

A dense arachnoid band encircles the

nerve at lateral end of IAC.

Posterocephalad to cochlea

Anteromedial to ampulla of SCC

Posterior to vestibule


17/69

Applied Anatomy :

Bottle neck at the entrance of facial nerve

predisposes it to strangulation in cases of edematous

swelling

This is the only segment of facial nerve in which there

are no anastomosing arterial arcades


18/69

Geniculate Ganglion :

On entering the facial canal there isan angulation of 132 degree as well

as downward inclination of 3-5mm.

At the GG Facial nerve takes 75

degree turn posteriorly at first genu.

Greater superficial petrosal nerve

arises from GG and emerges through

facial hiatus onto the floor of MCF

Contains bipolar ganglions for

sensory function of nerves

intermedius


19/69


20/69

Tympanic segment

From the GG facial nervecourses in tympanic segmentand measures approx 10-12mmin length.

Anteriorly it lies above and

medial to Processuscochleariformis

Slopes downward at an angle of30 degree to horizontal

In middle part it runs over the

oval window (superior margin)It then runs under Lateral

semicircular canal

Nerve then takes a second turn

Angle between 2nd and 3rd part

varies from 95-125 degree.


21/69


22/69

Mastoid Segment : Approx midway in

mastoid segment facialnerve gives off chordatympani.

Gives rise to Branch to

stapediusFacial nerve leaves the

temporal bone atSMF.As the nerve

approaches the SMF itbecomes encircled byfibrous tendon ofdigastric muscle whichbecomes part of nervesheath.


23/69


24/69


25/69


26/69

ac


27/69

Extratemporal Part: As it emerges from

SMF, extratemporal

FN runs anteriorly in

the substance of

parotid gland ,crosses

the external carotid

artery and divides at

the posterior border of

ramus of mandible

2 divisions : temporo-

facioal and cervico-

facial


28/69


29/69

Functional components of the Facial

Nerve (CN VII)SVE (Special Visceral Efferent) Motor to

striated muscles derived from the 2ndbranchial arch.

GVA (General Visceral Afferent) Sensoryfrom visceral touch, temperature, andpain.SVA (Special Visceral Afferent) Taste

GVE (General Visceral Efferent) Autonomic innervation to mucosal,lacrimal, and salivary glands.GSA (General Somatic Afferent) Sensory

from somatic touch, temperature, andpain.

1.

2.

3.

4.

5.

Click on numbers for functional components


30/69

SVE Component of the

Facial NerveThe next slides demonstrate innervation to muscles

derived from the 2nd branchial arch:

1. Stapedius muscle -- dampens movement of theossicles (inserts on stapes of middle ear)

2. Posterior auricular muscle -- posterior movementof pinna

3. Stylohyoid muscle -- elevates hyoid bone

4. Posterior belly of digastric -- elevates hyoid bone,

depresses mandible5. Muscles of facial expression -- blinking, smiling,

frowning, facial movements

Click here to start Animation of SVE component

S f


31/69

Stapedius muscle

dampens

movement of

ossicles.

Summary of

SVE

Facial

canal

Internal Acoustic

Meatus

Stylomastoid

Foramen

Click here to start

Temporal-orbicularis oculicloses eyelids.

Zygomatic-zygomaticus major

partly responsible for smiling.

Buccal-buccinator tenses cheek

Mandibular-depressor angularis

oris responsible for frowning.

Cervical- platysma helps lower

mandible and tightens skin of

neck.

Posterior auricular

muscle responsible for

posterior displacement

of pinna.

Facialnerve

Facialnerve

Posterior belly

of digastric

elevates hyoid

bone.

Stylohyoid muscle

elevates hyoid bone.

Posterior

auricular N.

Facial

nucleus


32/69

GVA Component of the Facial

NerveThe next slide demonstrates that GVA is

responsible for providing:1. Light touch, temperature, and pain

sensation from the soft palate via the

greater superficial petrosal nerve(GSPN).

Click here to start GVA

Through the


33/69

Through the

hiatus of canal of

GSPN

Light touch,

temperature,

and pain from

the soft palate

Through the

internal acoustic

meatus

Summary

of GVA

Through the

Pterygoid canal

Click here for animation

Pterygoid

canal

Facial

canal

Through thelesser palatine

canalGSPN

Facial nerve


34/69

SVA Component of the

Facial NerveThe next two slides demonstrate that SVA

is responsible for providing:

1. Taste from the hard and soft palate viathe greater superficial petrosal nerve(GSPN).

2. Taste from the anterior 2/3 of thetongue via the chorda tympani nerve.

Click here foranimation



35/69

Taste from hard

and soft palate.

Summary

of SVALacerate foramen

Click here to start animation

Facial

canal

Internal

Acoustic

Meatus

Stylomastoid

Foramen


superficial petrosal nerve

Taste from

anterior 2/3

tongue.

Pterygoid

canal

Chorda tympani

GSPN

Petrotympanic

fissure

Greater and

lesser palatine

canals

GVE C t f th


36/69

GVE Component of the

Facial Nerve1. Via the pterygopalatine ganglion GVE provides:

A. Lacrimation (tearing of the eye)

B. Mucus secretions of the nasal cavity

C. Mucus secretions of the oral cavity

2. Via innervation of the submandibular ganglion

GVE provides:A. Salivation of the oral cavity

Click to start Animation of GVE component


37/69


38/69

GSA Component of the

Facial NerveGSA is responsible for providing:

1. Touch, temperature, and pain sensation frompart of the external acoustic meatus via theposterior auricular nerve.

Click here to start GSA


39/69


40/69

Middle cerebral artery supplying the motor cortex.The facial nucleus in the pons is supplied by the anterior

inferior cerebellar artery and the short and longcircumferential arteries.

The facial nerve proper is then supplied by the1) labyrinthine branch of anterior inferior cerebellar artery2) superior petrosal branch of the middle meningeal artery3) the stylomastoid branch of the postauricular artery

These tend to overlap; however, the region just proximal to

the geniculate ganglion is thought to be somewhatsusceptible to vascular compromise secondary to thepoorer redundancy present there compared with otherareas.

Blood Supply


41/69

Radiological appearance :


42/69

Landmarks For Facial nerve During Mastoid

SurgeryLSCC Nerve lies inferior

Short process of Incus nerve is just medial to it

Oval window niche nerve lies superior

Chorda tympani nerve nerve arises from verticalsegment 4 mm above SM foramen

Processus cochleariformis nerve lies superior andmedial

Cog : bony prominencce from roof of epitympanum

7th nerve - LSCC 1.77 mm

7th nerve - SPI 2.36 mm

LSCC - SPI 1.25 mm


43/69


44/69

Landmarks For Facial nerve During Parotid

Surgery Tragal pointer nerve is 1cm deep and below to tip of tragal

cartilage. Not reliable

Tympano-mastoid suture line nerve lies 6-8mm deep to suture line

Post belly of Diagastric nerve is just superior to ant border Stylomastoid Foramen


45/69

Retrograde

1. Marginal mandibular nerve - nervecrosses superficial to facial v. 1cm

anterior to angle of mandible

2. Buccal branch nerve is 1cm above

and parallel to parotid duct

3. Temporal-bisects line from tragus to

lateral canthus.


46/69

Anatomic variations

Congenital bony dehiscence in facial canal (50 % temporal bones )

- Horizontal part (91 %)

- Vertical Part

Aberrations along tympanic segment

- the superior aspect of LSC

- the oval window (below it or partly above and partly below)

- the stapedial arch

Aberrations along vertical segment

- Abn posterior,lateral course

- Bifurcation,trifurcation posterior to OW

- Hypoplasia of facial nerve


47/69


48/69

Causes of facial paralysisCauses of facial paralysis


49/69


50/69

Investigations


51/69

InvestigationsThrough history and physiological examinationLaboratory studies

AudiometryIn selected cases in which either the location or site

of injury is unknown, both CT scanning and MRI maybe helpful.High-resolution CT scanning of the temporal bone

provides the best imaging of the bony confines of thefacial nerve and may reveal the site of pathology atany point along its course.MRI is superior in delineating the details of the soft

tissues, including the nerve itself. Thus it is the studyof choice to diagnose acoustic neuromas and facialnerve schwannomas.Electrophysiological & topodiagnostic tests


52/69

ELECTROPHYSIOLOGICAL

TESTS Nerve Excitability Test (NET) Maximal Stimulation Testing (MST)

Electromyography (EMG) Electroneurography (ENoG)

The two most helpful are the ENoG and EMG.


53/69

Nerve Excitability Test


54/69

Nerve Excitability Test(NET)Benefits:Easy to performMore comfortable for patient

DrawbacksSubjectivity (relies on operators

visual detection of response)May exclude smaller fibers (current

thresholds are likely to selectivelyactivate larger fibers with lowerthresholds and smaller fibers closer tostimulating electrode)


55/69

Maximal stimulation test (MST)

Measures greatest amplitude of facial movementon maximal or supramaximal stimuli ( up to 5mAor discomfort) expressed as percentage

Proportions of fibres that have degenerated canbe estimated so can guide prognosis andtreatment

Takes 3 4days for test to become positive

Maximal Stimulation Test


56/69

Maximal Stimulation TestElectrical impulse administered to saturate the nerve

with current and to compare it to contralateral side

Test is repeated periodically until definitive response

Response

Equivalent to contralateral side

Minimally diminished ( 90%No response within first ten days incomplete recovery

with significant sequelae

Superior to NET - test becomes abnormal sooner, but

drawback is subjectivity

k d l h ( G)


57/69

Evoked electromyography (EEMG)or Electroneuronography (EnoG)

Records compoundmuscle action potential(CMAP) with surfaceelectrodes placedtranscutaneously in the

nasolabial fold(response) andstylomastoid foramen(stimulus)

Waveform responses areanalyzed to comparepeak-to-peakamplitudes betweennormal and uninvolved

sides where the peakam litude is

E k d l h (EEMG)


58/69

Evoked electromyography (EEMG)or Electroneuronography (EnoG)

Most reliable in first 2-3 weeks post event (as neuropraxic fibersrecover or regenerate, they discharge asynchronously and theresponse is subsequently diminished)

Response < 10% of normal in first 3 weeks poor prognosis

Response > 90% of normal within 3 weeks of onset 80-100%probability of recovery

Testing every other day

Advantages: Reliable

Disadvantages:UncomfortableCostTest-retest variability due to position of electrodes


59/69

EMG

Measured by electrodes inserted in to orbicularis orisand orbicularis occuli muscles

EMG can be used to determine if a nerve in question isin fact in continuity (volitional activity recorded), showsevidence of Wallerian degeneration (fibrillationpotentials), or has signs of reinnervation (polyphasicinnervation potentials).

Fibrillation potentials typically arise 2-3 weeks followinginjury

Polyphasic reinnervation potentials may precede clinicalsigns of recovery by 6-12 weeks.

No potential muscle not viable

A ti R fl E k d


60/69

Acoustic Reflex Evoked

PotentialScalp recorded potential at 12 15 ms in response toacoustic stimulation C/L to recording site

Doubtful value


61/69

Magnetic stimulation testNoninvasiveNo pain/discomfort

Transcranial stimulation can be doneMay not be useful for prognostic purpose


62/69

Muscle biopsyUseful adjunct to EMG in long standing facialparalysis and in congenital facial paralysiswith suspected U/L absence of facial nerve

Deciding factor for reanimation proceduresMuscle viable dynamic procedures

Muscle not viable static procedures


63/69

Topodiagnostic Tests

1. Lacrimal functions(GSPN)

Schirmers test

2. Stapedius reflex (N. to Stapedius)

3. Taste and electrogustometry (ChordaTympani N.)

4. Salivary flow (Chorda Tympani N.)

5. Salivary pH (Chorda Tympani N.)


64/69

Schirmer Test Greater superficial petrosal nerveFilter paper is placed in the lower conjunctival fornix

bilaterally5x35mm filter paper hooked in lower fornix

for 5 min.Modified Schirmers test ammonium inhalation. Test is

not affected by corneal anesthesia

3- 5 minutes

Value of 25% or less on the involved side or total

lacrimation


65/69

Stapedial ReflexStapedius branch of the facial nerveMost objective and reproducibleA loud tone is presented to either the ipsilateral or

contralateral ear evokes a reflex movement of thestapedius muscle changes the tension on the TM(which must be intact for a valid test) resulting in achange in the impedance of the ossicular chain

If intact stapedial reflex, complete recovery can be

expected to begin within six weeksabsent reflex or reflex < 50% of amplitude of C/L sideis abnormal

Absence of the stapedial reflex during the first twoweeks in Bells Palsy is common


66/69

Taste TestingChorda tympani

Extremely subjective

Papillae generally disappear within 10 days postinjury - middle 1/3 of the tongue is most indicative,

because the anterior 1/3 may receive bilateral

input.

Electrogustometry positive if >25% difference on twosides


67/69

Salivary flow ratesChorda tympaniCannulation of Wharton's ducts bilaterally

5 minute measurement of outputSignificant if 25% reduction in flow of the

involved side as compared to the normal side

Salivary pH Flow Rate ( 6.1 incomplete

recovery)

Salivary flow of submandibular gland (< 45%of the healthy side poor prognosis)


68/69


69/69

19. facial nerve anatomy and its disorders

Documents