Facial Nerve and Its Clinical Importance

Facial nerve and its clinical importance

1. Fuad Ridha Mahabot
1

2. Introduction
•Isamixnerve,containingmotor,sensory,
taste,andsecretomotorfunction
•Primarilyisamotorfunctionforfacial
expression.
•Thereare2efferentand2afferentpathways
•Thefacialn.composedof10,000neurons
•7,000aremyelinated-motorfunction
•3,000areunmyelinated-sensory+
secretomotor+tastefunction
•70%motorroot
2

3. Functions
1.Specialvisceralefferent:
✓Motorfx:allmusclesfrom2ndbranchialarch;muscleoffacialexpression,auricular
muscle,stylohyoid,postbellydigastric&stapediusmuslce.
2.Generalvisceralefferent:
✓Secretomotorfx:tolacrimal,submandibular,sublingualglands&smallsecretorynasal
gland.
3.Specialvisceralafferent:
✓Tastefx:
•fromanterior2/3oftongue–viachordatympanin.
•fromhardpalate–viagreatersuperficialpetrosaln.
4.Greatersomaticafferent:
✓Sensoryfx:Bringsensationfromconcha,posterosuperiorEAC,postauricularskin,part
ofmucusmembraneatsupratonsillarrecess
3

4. Nucleus of CN VII
TheFacialn.have4nucleus:
1.Facialmotornucleus-motorfunction
2.Superiorsalivatorynucleus-secretomotor
function
3.Tractussolitariusnucleus-receivedtaste
function
4.Trigeminalnucleus-receivedsomato-
sensoryfunction
4

5. voluntary responses of the Facial muscles arise from
efferent discharge from the motor face area of the
cerebral cortex (precentral & postcentral gyri)
via corticobulbar tract to the internal capsule
lower brain stem (pons) where Facial nerve nucleus
situated.
Supranuclearorganization
5

6. Motor nucleus
•Locatedindeepcenterpons.
•Embryologicallyoriginatlowerthird
ofponsbeneaththe4thventricle
•Nucleusdividedintoupperpart&
lowerpart
✓Upperpart:receivefibresfromboth
ipsilateral+ contralateral
hemisphere
•Innervatedforeheadmuscles
✓Lowerpart:receivefibresfrom
contralateralonly
•Innervateslowerfaces
6

7. Course
Cortex & internal capsule
Facial nerve
nucleus
Intracranial
intratemporal
extracranial
7

8. 8

9. Intracranial part
From pons to internal acoustic meatus (IAM)
Distant ~ 15-17mm
The motor root
emerges at lower border of pons above the olive
The nervous intermedius
emerges btwn pons and inferior cerebellar peduncle
Together cross the CPA medial to VIII nerve
They run laterally & forwards to reach IAM.
9

10. •MotorFibers
✓motorfibresstartfromfacialmotornucleusinpons.itrunforwards&dorsallytowards
thefloorof4thventricle,wraparoundthenucleusoftheabducentnerve,thenrun
laterallytojointhesensoryroottoleavethebrainstemonlateralaspect
(pontomedullaryjunction)
•Sensoryroot(nervousintermedius)enterthebrainstemas
separatenerve.Itcarries:
1.somatosensoryfiberfromconchalskin&supratonsillarrecess–trigeminalnucleus
2.tastefiberfromthepalateandanterior2/3oftongue–nucleusoftractussolitarius
3.secretomotorfiberfromsubmandibular,sublingual,nasalandlacrimalgland–
superiorsalivarynucleus
10

11. 11

12. Intratemporal part
•FromIAMtostylomastoid
foramen
•Subdividedinto:
1.Meatalsegment
2.Labyrinthinesegment
3.Tympanic/horizontalsegment
4.Mastoid/verticalsegment
12

13. 1.Meatal segment
•Within IAM (porus)
Distant ~ 8-10mm length
Motor root located above the VIII n.
The nervusintermediuslocated in between
Accompanied with labyrinthine vessels
13

14. •Atthefundus:
✓the2rootsjointogetherthenenter
theFallopiancanal
✓Situatedanterosuperiorly
✓ThenervesurroundedbyC.S.F
✓Separatedfromsuperiorvestibularn.
bybill’sbar(verticalridge)&fromthe
cochlearn.bycristafalciformis
(transverseridge)
14

15. 2.Labyrinthine segment
•FromfundusofIAMtothegeniculateganglion.
•Thenerveinthissegmenthasnarrowestdiameter(0.61-0.68mm).
•thebonycanalhereisalsothenarrowest.
✓thus,edema/inflammationcaneasilycompressthenerveandcauseparalysis.
•Thisisalsotheshortestsegment~only4.0mmlength.
15

16. •Run between cochlea anteriorly, & superior SCC posteriorly & vestibule inferiorly
•Within the Fallopian canal
•The nerve reach the medial wall of the epitympanic recess
16

17. •Itturnssharplybackwardsinangleof60degree,forming1stgenu.
•Atthisturnliesthegeniculateganglion(reddishswelling)
17

18. 3.Tympanic / horizontal segment
•Fromgeniculategangliontojustabovethepyramidaleminence
✓markedbyprocessuscochleariformis
•geniculateganglionliesjustanteriortoit
•thetympanicsegmentstartatthislevel
•Itrunsposteriorlyonthemedialwalloftympaniccavity.
•Itsurroundedbybonyshell
✓buttheboneisthinandmaybedehiscense
•Itrunsabovetheovalwindow&promontory,andbelowtheprominenceof
lateralSCC
18

19. 19

20. •Abovetheovalwindow,thenerveslopes
downwards&backwardsatangleof30
degreefromthehorizontal.
•thenervecurveinferiorlytoenterits
mastoidsegmentatthepyramid.(2nd
genu)–btwtympanicsegment&mastoid
segment.
•Atthisturntheshortprocessofincus
alwayslieslateraltothenerve.
•Lengthofthissegment~11mm
20

21. 4.Mastoid / vertical segment
•Fromthepyramidtostylomastoidforamen.
•Liesposterioranddeeptothetympanicannulusandtympanomastoid
suturelineintheposteriorwallofEAC.
•Liesdeepwithinthemastoid,rarelylessthan18mmfromoutersurfaceof
theboneinadult.
•Length~13mm
•2branches:
✓Nervetostapedius
✓Cordatympaninerve
21

22. 22

23. Extracranial segment
•Fromthestylomastoidforamentothe
terminationofitsperipheralbranches.
•Length~15-20mm
•Thedigastricgrooveintheinferiorsurfaceof
themastoidprocessisalandmarkthatleadsto
stylomastoidforamen.
(postbellydigastricattachtothedigastric
groove)
•Then,thenerveturnsforwardandrunslateral
tothebaseofstyloidprocess,toenterthe
parotidgland.
23

24. •Intheparotidgland,thenerveseparatesinto2primarydivisions
1.temporofacial–temporal,zygomatic.
2.cervicofacial–buccal,marginalmandible,cervical.
•eachofdivisiondividesintoseveralbrancheswhichinterconnectasparotidplexus
✓fromthisplexusarisetheterminalbranchofthefacialnerve
24

25. 25

26. Branches of facial nerve
A.Branchfromgeniculateganglion
1.Greatersuperficialpetrosalnerve(GSPN)
B.Brancheswithinfacialcanal
1.Stapediusnerve
2.Chordatympaninerve
C.Branchesintheneck&face
1.Postauricularnerve.
2.Digastricnerve.
3.Stylohyoidnerve.
D.Brancheswithinparotidgland
1.Temporalnerve
2.Zygomaticnerve
3.Buccalnerve
4.Marginalmandiblenerve
5.Cervicalnerve
26

27. Greater superficial petrosalnerve (GSPN)
•Fx:
✓Receivetastefibrefromhardpalate
✓BringSecretomotorfibre,synapseinthepterygopalatineganglion,thencarriedby:
•zygomaticnerve>>lacrimalnerve>>lacrimalgland
•Nasal+palatinenerve>>nasal+palatinegland
•itleavesthegeniculateganglionanteriorly,runforwards.
✓receivesatwigfromtympanicplexus
✓itentermiddlecranialfossa,andrunbeneathtrigeminalgangliontojointhedeep
petrosaln.(fromsympatheticplexusonI.C.A)attheforamenlacerumtoformthen.of
thepterygoidcanal(vidiannerve)
•Itrunsinthecanaltoendatthepterygopalatineganglion
27

28. 28

29. Nerve to Stapedius
•arisefromthemastoid/verticalsegment
•reachthestapediusmusclethroughcanalatthebaseofpyramid
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30. Cordatympani nerve
•Arise6mmabovethestylomastoidforamen
•Runsupwardandforward,enterthetympaniccavitythroughposterior
canaliculusatthejunctionoftheposterior&lateralwalls
•ItrunsacrossthemedialsurfaceoftheTMbetweenthemucosal&fibrous
layers
•Itpassesbtwincusandupperportionofthehandleofmalleus,abovethe
tendonoftensortympanimuscle
30

31. •Itcontinuesforwardtoleavethetympaniccavitybytheanteriorcanaliculus
whichthenjointhepetrotympanicfissuretoenterinfratemporalfossa
•Ininfratemporalfossa,itcrossthemedialsurfaceofthespineofsphenoid,
passdeeptolateralpterygoidmuscletojointhelingualnerve
•Chordatympanicarries:
✓Secretomotorfibreswhichenterthesubmandibularganglion+synapse-thensupply
thesubmandibular&sublingualgland
✓Themajorityarethetastefibresfromant2/3oftongueexceptvallatepapillae
31

32. 32

33. 33

34. 34

35. Branches in the neck & face
1.Postauricularn.:
✓ariseclosetothestylomastoidforamen
✓runupbetweentheEAC&ant.surfaceofmastoid
✓supplytheposteriorauricularm.,intrinsicm.ofthepost.aspectofpinna,occipitalm.
2.Digastricnerve:
✓ariseclosetostylomastoidforamen
✓supplyposteriorbellyofDigastric
3.Nervetostylohyoid:
✓supplystylohyoidm.
✓arisenearorinconjunctionwithDigastricn.
4.Haller’sansa*
✓occassionalsmallanastomoticbranchoftheglossopharyngealnerve
*Swartz JD: The facial nerve canal: CT analysis of the protruding tympanic segment. Radiology 153:443-447, 1984 35

36. 36

37. 37

38. Branches from parotid plexus
(temporofacial)
1.Temporalbranch
✓Crosszygomaticarchsupplyintrinsic
muscleonlateralsurfaceofauricleand
anterior&superiorauricularmuscles
✓Otherbranchessupplyfrontalbellyof
occipitofrontalis,orbicularisoculi&
corrugator
2.Zygomaticbranch
✓Runparalleltozygomaticarch
innervateorbicularisoculi
✓Someoflowerbranchmayjoinwith
buccalbranchforminfraorbital
plexusinnervatemuscleinmiddle
partofface
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39. Branches from parotid plexus
(cervicofacial)
3.Buccalbranch
✓Passeshorizontallyforwardtomuscle
middlepartofface(procerus,
orbicularisoculi,zygomaticus,levator
angulioris,levatorlabiisuperioris,
buccinator,orbicularisoris&small
muscleofnose)
4.Mandibularbranch
✓Runsforwardbelowangleofmandible
underplatysmathenturnsupwards
&forwardstocrossmandibleunder
coverofdepressorangulioris(&
supplyit)continuesonwards
supplyorbicularisorisandother
muscleoflips&chin
5.Cervicalbranch
✓Leaveslowerpartofparotidgland
runsdownneckundercoverof
platysma(&supplyit)
39

40. Blood supply
•Intracranialpart
✓ant.inf.cerebellarartery(motornucleus)
✓superficialpetrosalbr.ofmiddlemeningealartery
•Intratemporal
✓stylomastoidbranchfrompost.auricularartery
•Extratemporal
✓stylomastoidartery
✓posteriorauricularartery
✓superficialtemporalartery
✓transversefacialartery
40

41. 41

42. Venous Drainage
•Formsaplexusaroundthenerve
•Efferentveinrunfromtheplexusthroughthesheathtolieonitsoutersurface
•Fromtheintratemporalpart
✓Veinsleavesthecanalatstylomastoidforamentoenterthevenaecomitantesof
stylomastoidartery
✓Veinsleavesthen.atgeniculumtoenterthevenaecomitantesofsuperficialpetrosal
artery
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43. Applied Anatomy
•Supranuclearlesionparalysisof
contralaterallowerface
•Infranuclearlesionparalysisof
ipsilateralface(upper&lower)
•Corticobulbartractsfromupperface
decussateincompletelyinpons,sothese
muscleshavebilateralsupranuclear
innervation,whiletractstolowerface
decussatecompletelysotheyhave
contralateralinnervationsonly
43

44. Schimer’s test:
-↓ lacrimation
lesion proximal to
geniculate ganglion
Stapedial reflex:
-loss reflexlesion
above nerve to
stapedius muscle
Taste test:
-impaired taste
lesion above
chorda tympani
Submandibular
salivary flow test:
-↓ salivation
lesion above chorda
tympani
Topodiagnostic test
44

45. Surface Markings
Facialnervetrunk:
•Thetrunkexitstheskullatthestylomastoidforamen
•Thisissituatedatthedeependofthetympanomastoidsutureline,belocatedatthejunction
betweenthemastoidprocessandthetympanicringoftheexternalearcanal
Temporal(frontal)branchoffacialnerve:
•Thenervecrossesthezygomaticarch
•ItrunswithintheSMASandliessuperficialtothedeeptemporalisfascia.
•Itcoursesmoreorlessalongalinedrawnbetweentheattachmentofthelobuleoftheear
toapoint1.5cmabovethelateralaspectoftheeyebrow
•Toavoidinjurytothetemporalbranchdissecteitherinasubcutaneousplaneordeeptothe
SMAS
45

46. Identification of Facial Nerve During Parotid
Surgery
•Inferiorportionofthecartilaginousexternalauditorycanal.The
facialnervelies1cmdeepandinferiortoitstip
•Groovebetweenthecartilagiousandbonyexternalauditory
meatus.Thefacialnerveliesimmediatelydeepandinferiortothisatits
pointofexitfromskull
•Anteriorborderoftheposteriorbellyofthedigastricmuscle.The
facialnerveleavestheskullimmediatelyanteriortotheattachmentofthis
muscle.Itcanbeexposedbycarefuldissectionintheareaimmediately
anteriortotheposteriorbellyofthedigastricintheregionofthemastoid
process
46

47. •Thefacialnerveisusuallyexploredbyprogradedissectioni.e.bylocatingthe
nervetrunkwhereitexitsfromthestylomastoidforamen,andthendissecting
anteriorlyalongthetrunk,thepesanserinusandthedivisionsandnerve
branches.
•Occasionallythisisnotpossiblee.g.withalargefixedmasscenteredatthe
stylomastoidforamen.Insuchcasesaretrogradedissectionmayberequired
✓temporalbranch-crossesthezygoma
✓buccalbranches-lieparalleltotheparotidduct
✓marginalmandibularbranch-iscrossesthefacialarteryandveinjustbeloworatthe
inferiormarginofthemandible,whereitisjustdeeptoplatysma
47

48. Buccal branches adjacent to the parotid duct
48

49. Marginal mandibular nerve crossing facial artery and vein
49

50. Identification of Facial Nerve During Mastoid
Surgery
•Thesuperiorlandmarksforthemastoidsegmentofthefacialnerve
✓lateralsemicircularcanal,-facialnerverunsanteroinferiorly
✓andtheposteriorsemicircularcanal-thenerveruns2.5mmanteriortoit.
•Findingthefacialnervealongdigastricridgeandthestylomastoidfibersisa
verysafewayofidentifyingthefacialnerveawayfromanymastoid
pathology.
•Digastricridge-isasmoothconvexbonefoundclosetothemastoidtip.
✓Itcanbedifficulttofindinpoorlypneumatisedtemporalbones.
✓Oncethesigmoidsinushasbeenskeletonisedthedigastricridgeisfoundbydrilling
inferiorlytothesinus,closetothemastoidtip,fromlaterallytomedially,inahorizontal
direction.
50

51. •Periostealfibresrunanteriorlyfromthedigastricridgeinaplane
perpendiculartotheridge.
✓Thefacialnervecanbelocatedproximaltothestylomastoidforamenbydrillingthelast
oftheseperiostealfibres.
✓Thesensorybranchoffacialnerve(whichinnervatestheposteriorwalloftheexternal
auditorycanalandaportionofthetympanicmembrane)justabovethestylomastoid
foramen.
•Watchoutforanearlytake-offofthechordatympaniclosetothe
stylomastoidforamen.
51

52. RelationsofVIIntoshortprocessofincus;
superiorsemicircularcanal(SCC);lateral
semicircularcanal(LSC);posteriorsemicircular
canal(PSC);dura;andsigmoidsinus
Distalportionofmastoidsegmentoffacialnerve
(arrow)isidentifiedclosetodigastricridge
52

53. Thank you
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