Facial Nerve Embryology, Facial Nerve Embryology, Anatomy, EvaluationAnatomy, Evaluation

Alice LeeAlice Lee

October 28, 2004October 28, 2004

Case presentationCase presentation

HPI: 20 yo M s/p fall from bike without helmet, + HPI: 20 yo M s/p fall from bike without helmet, + LOC, +EtOHLOC, +EtOH

PMH/PSH/Med/All/Fam hx/Soc hx: negPMH/PSH/Med/All/Fam hx/Soc hx: neg PEX: AVSS, A&O x3, PERRLAPEX: AVSS, A&O x3, PERRLA

Ears: R hemotympanum,BC>ACEars: R hemotympanum,BC>AC L TM WNL, AC>BC, Weber R L TM WNL, AC>BC, Weber RNose/OC/OP/Neck: WNLNose/OC/OP/Neck: WNLFace: Abrasions to R forehead, L lipFace: Abrasions to R forehead, L lipCN II-XII intactCN II-XII intact

CT head: WNLCT head: WNL Other injuries: R clavicle and scapula fxOther injuries: R clavicle and scapula fx

Case presentationCase presentation

Returns to ER 5 days from trauma with Returns to ER 5 days from trauma with acute onset of R facial paralysis and with acute onset of R facial paralysis and with R decreased hearingR decreased hearing

HB VI, R hemotympanum, R Weber, R HB VI, R hemotympanum, R Weber, R BC>ACBC>AC

CT temporal bone: Longitudinal R CT temporal bone: Longitudinal R temporal bone fracture, sparing otic temporal bone fracture, sparing otic capsulecapsule

2 week steroid taper, f/u clinic 5 days2 week steroid taper, f/u clinic 5 days

Facial nerve embryonic Facial nerve embryonic developmentdevelopment

Facial nerve course, branching pattern, and Facial nerve course, branching pattern, and anatomical relationships are established anatomical relationships are established during the first 3 months of prenatal lifeduring the first 3 months of prenatal life

The nerve is not fully developed until about The nerve is not fully developed until about 4 years of age4 years of age

The first identifiable FN tissue is seen at The first identifiable FN tissue is seen at the third week of gestation-the third week of gestation-facioacoustic facioacoustic primordium or crestprimordium or crest

Facial nerve embryology: 4Facial nerve embryology: 4thth weekweek

By the end of the 4By the end of the 4thth week, the facial and week, the facial and acoustic portions are acoustic portions are more distinctmore distinct

The facial portion The facial portion extends to placodeextends to placode

The acoustic portion The acoustic portion terminates on otocystterminates on otocyst

Facial nerve embryology: 5Facial nerve embryology: 5thth weekweek

Early 5Early 5thth week, the week, the geniculate gangliongeniculate ganglion formsforms

Distal part of Distal part of primordium separates primordium separates into 2 branches: into 2 branches: main main trunk of facial nervetrunk of facial nerve and and chorda tympanichorda tympani

Facial nerve embryology: 5Facial nerve embryology: 5thth weekweek

Near the end of the 5Near the end of the 5thth week, the week, the facial motor facial motor nucleusnucleus is is recognizablerecognizable

The motor nuclei of The motor nuclei of CN VI and VII initially CN VI and VII initially lie in close proximity. lie in close proximity. The The internal genuinternal genu forms as forms as metencephalon metencephalon elongates and CN VI elongates and CN VI nucleus ascendsnucleus ascends

Facial nerve embryology: 7Facial nerve embryology: 7thth weekweek

Early 7Early 7thth week, geniculate ganglion is well- week, geniculate ganglion is well-defined and defined and facial nerve rootsfacial nerve roots are are recognizablerecognizable

The The nervus intermedius nervus intermedius arises from the arises from the ganglion and passes to brainstem. Motor ganglion and passes to brainstem. Motor root fibers pass mainly caudal to ganglionroot fibers pass mainly caudal to ganglion

Can patients with congenital facial Can patients with congenital facial paralysis have intact taste? Why?paralysis have intact taste? Why?

Facial nerve embryology: 7Facial nerve embryology: 7thth weekweek

Facial nerve embryonic Facial nerve embryonic development: Intratemporal course development: Intratemporal course

and branchesand branches

Facial nerve embryonic Facial nerve embryonic development: Extratemporal development: Extratemporal

segment - branchessegment - branches Proximal branches form firstProximal branches form first 66thth week, posterior auricular week, posterior auricular

branch>branch of digastricbranch>branch of digastric Early 8Early 8thth week,temporofacial and week,temporofacial and

cervicofacial divisions cervicofacial divisions Late 8Late 8thth week, 5 major peripheral week, 5 major peripheral

subdivisions presentsubdivisions present

Facial nerve embryonic Facial nerve embryonic development: Extratemporal development: Extratemporal

segment – other nervessegment – other nerves Facial nerve communicates with peripheral Facial nerve communicates with peripheral

branches of CN V, IX, X, cervical cutaneous branches of CN V, IX, X, cervical cutaneous nervesnerves

greater auricular nerve and transverse cervical greater auricular nerve and transverse cervical branches of the cervical plexus (C2, C3)branches of the cervical plexus (C2, C3)

Trigeminal nerve: auriculotemporal, infraorbital, Trigeminal nerve: auriculotemporal, infraorbital, buccal, mental branchesbuccal, mental branches

All connections are complete by week 12 except All connections are complete by week 12 except for 4 (connections to branches of CN V at orbit for 4 (connections to branches of CN V at orbit periphery)-these are complete at 4.5 monthsperiphery)-these are complete at 4.5 months

Peripheral communications of facial Peripheral communications of facial nervenerve

Facial nerve embryonic Facial nerve embryonic development: Extratemporal development: Extratemporal

segment – Parotidsegment – Parotid

Anatomic segments of facial Anatomic segments of facial nervenerve

Intracranial: brainstem to IACIntracranial: brainstem to IAC Meatal: fundus of IAC to meatal foramen Meatal: fundus of IAC to meatal foramen

(narrowest aperture of FN’s bony canaliculus(narrowest aperture of FN’s bony canaliculus Labyrinthine: meatal foramen to geniculate Labyrinthine: meatal foramen to geniculate

ganglion (first genu)ganglion (first genu) Tympanic/horizontal: ganglion Tympanic/horizontal: ganglion adj to oval adj to oval

window window pyramidal eminence of stapedius pyramidal eminence of stapedius tendontendon

Mastoid/vertical: second genu to SM foramenMastoid/vertical: second genu to SM foramen Extratemporal: SM foramen to facial musclesExtratemporal: SM foramen to facial muscles

3-D t bone3-D t bone

Facial nerve: types of fibersFacial nerve: types of fibers

Special Visceral Efferent/Branchial MotorSpecial Visceral Efferent/Branchial Motor General Visceral Efferent/ParasympatheticGeneral Visceral Efferent/Parasympathetic General Sensory Afferent/SensoryGeneral Sensory Afferent/Sensory Special Visceral Afferent/TasteSpecial Visceral Afferent/Taste

Special Visceral Efferent/Branchial Special Visceral Efferent/Branchial MotorMotor

Premotor cortex Premotor cortex motor cortex motor cortex corticobulbar tract corticobulbar tract bilateral facial motor bilateral facial motor nuclei (pons) nuclei (pons) facial muscles facial muscles

Stapedius, stylohyoid, posterior digastric, Stapedius, stylohyoid, posterior digastric, buccinatorbuccinator

General Visceral General Visceral Efferent/ParasympatheticEfferent/Parasympathetic

Superior salivatory nucleus (pons) Superior salivatory nucleus (pons) nervus intermedius nervus intermedius greater/superficial petrosal nerve greater/superficial petrosal nerve facial facial hiatus/middle cranial fossa hiatus/middle cranial fossa joins deep petrosal nerve joins deep petrosal nerve (symp fibers from cervical plexus) (symp fibers from cervical plexus) thru pterygoid canal thru pterygoid canal (as vidian nerve) (as vidian nerve) pterygopalatine fossa pterygopalatine fossa spheno/pterygopalatine ganglion spheno/pterygopalatine ganglion postganglionic postganglionic parasympathetic fibers parasympathetic fibers joins zygomaticotemporal joins zygomaticotemporal nerve(V2) nerve(V2) lacrimal gland & seromucinous glands of lacrimal gland & seromucinous glands of nasal and oral cavitynasal and oral cavity

Superior salivatory nucleus Superior salivatory nucleus nervus intermedius nervus intermedius chorda chorda joins lingual nerve joins lingual nerve submandibular ganglion submandibular ganglion – postganglioic parasympathteic fibers – postganglioic parasympathteic fibers submandibular submandibular and sublingual glandsand sublingual glands

General Sensory Afferent/SensoryGeneral Sensory Afferent/Sensory

Sensation to auricular concha, EAC wall, Sensation to auricular concha, EAC wall, part of TM, postauricular skinpart of TM, postauricular skin

Cell bodies in geniculate ganglionCell bodies in geniculate ganglion

Special Visceral Afferent/TasteSpecial Visceral Afferent/Taste

Postcentral gyrus Postcentral gyrus nucleus solitarius –> nucleus solitarius –> tractus solitarius – nervus intermedius tractus solitarius – nervus intermedius geniculate ganglion – chorda tympani geniculate ganglion – chorda tympani joins lingual nerve joins lingual nerve anterior 2/3 tongue, anterior 2/3 tongue, soft and hard palatesoft and hard palate

_____ _____

Facial nerve blood supplyFacial nerve blood supply

Intracranial/Meatal: labyrinthine branches Intracranial/Meatal: labyrinthine branches from ant inf cerebellar arteryfrom ant inf cerebellar artery

Perigeniculate: superficial petrosal branch Perigeniculate: superficial petrosal branch of middle meningeal artery of middle meningeal artery

Tympanic/Mastoid: stylomastoid branch of Tympanic/Mastoid: stylomastoid branch of posterior auricular arteryposterior auricular artery

Nerve fiber componentsNerve fiber components

Epineurium – nerve sheath; vasa Epineurium – nerve sheath; vasa nervorumnervorum

Perineurium – surrounds endoneural Perineurium – surrounds endoneural tubules; tensile strength, protects against tubules; tensile strength, protects against infectioninfection

Endoneurium – surrounds axons, adherent Endoneurium – surrounds axons, adherent to Schwann layer, endoneural tubules to Schwann layer, endoneural tubules regeneration regeneration

Pathophysiology of nerve injury: Pathophysiology of nerve injury: Sedon classificationSedon classification

Neuropraxia – conduction blockade from Neuropraxia – conduction blockade from body to distal; distal nerve can still be body to distal; distal nerve can still be stimulated. External compress vs stimulated. External compress vs intraneural edemaintraneural edema

Axonotmesis – wallerian degeneration Axonotmesis – wallerian degeneration distal to lesion with distal to lesion with preservation of preservation of endoneural tubulesendoneural tubules

Neurotmesis – wallerian degeneration and Neurotmesis – wallerian degeneration and loss of endoneural tubules/regen layerloss of endoneural tubules/regen layer

Nerve injuryNerve injury

Causes of facial paralysisCauses of facial paralysisCauses of facial paralysisCauses of facial paralysis

h/o recurrent h/o recurrent alternating facial alternating facial paralysisparalysis

Recurrent orofacial Recurrent orofacial edema (lasts<48 hrs)edema (lasts<48 hrs)

chelitischelitis Fissured tongueFissured tongue What do I have?What do I have?

HB Facial Nerve GradingHB Facial Nerve Grading

Topognostic testingTopognostic testing

Mainly of historical interest; not prognosticMainly of historical interest; not prognostic Uses branching pattern of the facial nerve Uses branching pattern of the facial nerve

to identify site of lesion, but is not reliableto identify site of lesion, but is not reliable Tearing – Schirmer’s testTearing – Schirmer’s test Stapes reflex – Change in acoustic Stapes reflex – Change in acoustic

impedence caused by superthreshold impedence caused by superthreshold stimulus; stapedial branch of FN is the first stimulus; stapedial branch of FN is the first efferent branchefferent branch

Auditory testingAuditory testing

To eval for concurrent SNHL or CHLTo eval for concurrent SNHL or CHL CHL – middle ear tumors, cholesteatomas, CHL – middle ear tumors, cholesteatomas,

other processes involving tympanic other processes involving tympanic segmentsegment

SNHL – acoustic neuromas, meningiomas, SNHL – acoustic neuromas, meningiomas, congenital cholesteatoma, others involving congenital cholesteatoma, others involving CPA or IACCPA or IAC

Electrophysiologic testsElectrophysiologic tests

Measures nerve conduction; from proximal Measures nerve conduction; from proximal to injury site to muscle/evoked electrical to injury site to muscle/evoked electrical signal. signal.

Cannot measure proximal to stylomastoid Cannot measure proximal to stylomastoid foramenforamen

Require waiting until degeneration has Require waiting until degeneration has progressed enough to be detectable.progressed enough to be detectable.

Nerve stimulation testNerve stimulation test

NST -office-based, stim main branches with 1 NST -office-based, stim main branches with 1 millisec wave pulse, minimal thresholds for facial millisec wave pulse, minimal thresholds for facial muslce response are comparedmuslce response are compared

3.5 milliampere difference is pathologic; not 3.5 milliampere difference is pathologic; not sens to lesser degrees of nerve transmission sens to lesser degrees of nerve transmission that do not result in loss of visible face motionthat do not result in loss of visible face motion

Why can’t this test be used during the first 72 Why can’t this test be used during the first 72 hours after injury?hours after injury?

Maximal stimulation testingMaximal stimulation testing

Variation of NST, but uses maximal stimulation Variation of NST, but uses maximal stimulation at a level sufficient to depolarize all motor axons at a level sufficient to depolarize all motor axons under the stimulatorunder the stimulator

Stim 5 peripheral branches and main trunkStim 5 peripheral branches and main trunk Compares both sides; subj gradingCompares both sides; subj grading Bell’s – Equal B results up to 10 days, 92% with Bell’s – Equal B results up to 10 days, 92% with

full recovery. Response lost within 10 days, full recovery. Response lost within 10 days, 100% had incomplete return (May, et al)100% had incomplete return (May, et al)

Electroneuonography ENog/Electroneuonography ENog/Evoked electromyography EEMGEvoked electromyography EEMG

Similar to MST except the measured end Similar to MST except the measured end point is evoked muscle compound action point is evoked muscle compound action potential amplitudes and latencies (not potential amplitudes and latencies (not visible muscle movement); used after 2 visible muscle movement); used after 2 weeks of injuryweeks of injury

Recording electrodes on nasal alae, Recording electrodes on nasal alae, stimulator under zygomatic archstimulator under zygomatic arch

EEMGEEMG

The peak-to-peak The peak-to-peak amplitude is amplitude is proportional to the proportional to the number of intact number of intact motor axonsmotor axons

Example: 10% of Example: 10% of normal amplitude = normal amplitude = 90% degeneration90% degeneration

EEMG - tumorEEMG - tumor

EEMG – Bell’sEEMG – Bell’s

Progressive Progressive degeneration – 3,4,5 degeneration – 3,4,5 days post-onsetdays post-onset

MA = masseter MA = masseter artifact, can be artifact, can be confused with small confused with small evoked potential, ID evoked potential, ID by very short latencyby very short latency

ElectromyographyElectromyography

Measures activity of muscle (from Measures activity of muscle (from volitional contraction) instead of the nervevolitional contraction) instead of the nerve

Measured at insertion, voluntary Measured at insertion, voluntary contraction, at restcontraction, at rest

Helps to eliminate false positive Helps to eliminate false positive NET/MST/EEMGNET/MST/EEMG

Diagnostic, not prognosticDiagnostic, not prognostic

EMG – insertional, at restEMG – insertional, at rest

A – normal needle A – normal needle insertional activityinsertional activity(dec w/ muscular (dec w/ muscular fibrofatty changes)fibrofatty changes)

B – Positive sharp waves B – Positive sharp waves (denervation)(denervation)

C – *Fibrillations C – *Fibrillations (denervation 10-20d)(denervation 10-20d)

D – Bizarre formations D – Bizarre formations (myopathies, (myopathies, neuropathies)neuropathies)

Motor unit action potentialMotor unit action potential

The motor unit tested by EMG is only a small portion of The motor unit tested by EMG is only a small portion of the muscle fibers in an anatomic motor unitthe muscle fibers in an anatomic motor unit

Motor unit action potential/MUAP is the sum of early Motor unit action potential/MUAP is the sum of early discharges of some muscle fibers of one motor unitdischarges of some muscle fibers of one motor unit

Nl MUAP: bi/triphasic, amp 0.3-0.5mv, duration 3-16msNl MUAP: bi/triphasic, amp 0.3-0.5mv, duration 3-16ms

EMGEMG A, inserting needle activity. For A, inserting needle activity. For

suspected muscle atrophy-suspected muscle atrophy-reanimation usu doesn’t work 2 reanimation usu doesn’t work 2 not enough muscle present. not enough muscle present.

B. Fibrillation potentials can be B. Fibrillation potentials can be seen in conduction block and seen in conduction block and complete disruptioncomplete disruption

C. Contracting muscle/smile. C. Contracting muscle/smile. Polyphasic potentials indicative of Polyphasic potentials indicative of early nerve regenration; early nerve regenration; polyphasic patterns can be seen polyphasic patterns can be seen in myopathiesin myopathies

D. Recruitment/interference D. Recruitment/interference assessed my maximal contraction assessed my maximal contraction of a muscle groupof a muscle group

Limitations of electrophysiologic Limitations of electrophysiologic testingtesting

72 hours delay for MST and EEMG72 hours delay for MST and EEMG EMG delay ~14 days until fibrillations seenEMG delay ~14 days until fibrillations seen Normal variations can be great. EEMG Normal variations can be great. EEMG

response of 50% have been seen in response of 50% have been seen in normal controls.normal controls.

Must correlate clinical findings with resultsMust correlate clinical findings with results Future? Magnetic nerve stimulation for Future? Magnetic nerve stimulation for

intracranial stim/stim prox to lesionintracranial stim/stim prox to lesion

ReferencesReferences

May – The Facial NerveMay – The Facial Nerve Burgess – Reanimation of the Paralyzed FaceBurgess – Reanimation of the Paralyzed Face Rubin – The Paralyzed faceRubin – The Paralyzed face Netter – Collection of Medical Illustrations, Vol I:Nervous SystemNetter – Collection of Medical Illustrations, Vol I:Nervous System May M, Blumenthal FS, Klein SR: Acute Bell’s palsy: prognostic value of evoked May M, Blumenthal FS, Klein SR: Acute Bell’s palsy: prognostic value of evoked

electromyography, maximal stimulation, and other electrical tests. Am J Otol 5: 1, electromyography, maximal stimulation, and other electrical tests. Am J Otol 5: 1, 1983.1983.

Darrouzet, et al. Management of facial paralysis resulting from temporal bone Darrouzet, et al. Management of facial paralysis resulting from temporal bone fractures: Our experience ein 115 cases. Otol-Head Neck Surg 125:77-84, 2001.fractures: Our experience ein 115 cases. Otol-Head Neck Surg 125:77-84, 2001.

Jenny AB et al. Organization of the facial nucleus and corticofacial projection in the Jenny AB et al. Organization of the facial nucleus and corticofacial projection in the monkey: a reconsideration of the upper motor neuron palsy. Neurology 37:930-939, monkey: a reconsideration of the upper motor neuron palsy. Neurology 37:930-939, 1987.1987.