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Facial Nerve Embryology, Anatomy, Evaluation Alice Lee October 28, 2004.

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Presentation on theme: "Facial Nerve Embryology, Anatomy, Evaluation Alice Lee October 28, 2004."— Presentation transcript:

1 Facial Nerve Embryology, Anatomy, Evaluation Alice Lee October 28, 2004

2 Case presentation  HPI: 20 yo M s/p fall from bike without helmet, + LOC, +EtOH  PMH/PSH/Med/All/Fam hx/Soc hx: neg  PEX: AVSS, A&O x3, PERRLA Ears: R hemotympanum,BC>AC L TM WNL, AC>BC, Weber R Nose/OC/OP/Neck: WNL Face: Abrasions to R forehead, L lip CN II-XII intact  CT head: WNL  Other injuries: R clavicle and scapula fx

3 Case presentation  Returns to ER 5 days from trauma with acute onset of R facial paralysis and with R decreased hearing  HB VI, R hemotympanum, R Weber, R BC>AC  CT temporal bone: Longitudinal R temporal bone fracture, sparing otic capsule  2 week steroid taper, f/u clinic 5 days

4 Facial nerve embryonic development  Facial nerve course, branching pattern, and anatomical relationships are established during the first 3 months of prenatal life  The nerve is not fully developed until about 4 years of age  The first identifiable FN tissue is seen at the third week of gestation-facioacoustic primordium or crest

5 Facial nerve embryology: 4 th week  By the end of the 4 th week, the facial and acoustic portions are more distinct  The facial portion extends to placode  The acoustic portion terminates on otocyst

6 Facial nerve embryology: 5 th week  Early 5 th week, the geniculate ganglion forms  Distal part of primordium separates into 2 branches: main trunk of facial nerve and chorda tympani

7 Facial nerve embryology: 5 th week  Near the end of the 5 th week, the facial motor nucleus is recognizable  The motor nuclei of CN VI and VII initially lie in close proximity. The internal genu forms as metencephalon elongates and CN VI nucleus ascends

8 Facial nerve embryology: 7 th week  Early 7 th week, geniculate ganglion is well- defined and facial nerve roots are recognizable  The nervus intermedius arises from the ganglion and passes to brainstem. Motor root fibers pass mainly caudal to ganglion  Can patients with congenital facial paralysis have intact taste? Why?

9 Facial nerve embryology: 7 th week

10 Facial nerve embryonic development: Intratemporal course and branches

11 Facial nerve embryonic development: Extratemporal segment - branches  Proximal branches form first  6 th week, posterior auricular branch>branch of digastric  Early 8 th week,temporofacial and cervicofacial divisions  Late 8 th week, 5 major peripheral subdivisions present

12 Facial nerve embryonic development: Extratemporal segment – other nerves  Facial nerve communicates with peripheral branches of CN V, IX, X, cervical cutaneous nerves  greater auricular nerve and transverse cervical branches of the cervical plexus (C2, C3)  Trigeminal nerve: auriculotemporal, infraorbital, buccal, mental branches  All connections are complete by week 12 except for 4 (connections to branches of CN V at orbit periphery)-these are complete at 4.5 months

13 Peripheral communications of facial nerve

14 Facial nerve embryonic development: Extratemporal segment – Parotid

15 Anatomic segments of facial nerve  Intracranial: brainstem to IAC  Meatal: fundus of IAC to meatal foramen (narrowest aperture of FN’s bony canaliculus  Labyrinthine: meatal foramen to geniculate ganglion (first genu)  Tympanic/horizontal: ganglion  adj to oval window  pyramidal eminence of stapedius tendon  Mastoid/vertical: second genu to SM foramen  Extratemporal: SM foramen to facial muscles

16 3-D t bone

17 Facial nerve: types of fibers  Special Visceral Efferent/Branchial Motor  General Visceral Efferent/Parasympathetic  General Sensory Afferent/Sensory  Special Visceral Afferent/Taste

18 Special Visceral Efferent/Branchial Motor  Premotor cortex  motor cortex  corticobulbar tract  bilateral facial motor nuclei (pons)  facial muscles  Stapedius, stylohyoid, posterior digastric, buccinator

19 General Visceral Efferent/Parasympathetic  Superior salivatory nucleus (pons)  nervus intermedius  greater/superficial petrosal nerve  facial hiatus/middle cranial fossa  joins deep petrosal nerve (symp fibers from cervical plexus)  thru pterygoid canal (as vidian nerve)  pterygopalatine fossa  spheno/pterygopalatine ganglion  postganglionic parasympathetic fibers  joins zygomaticotemporal nerve(V2)  lacrimal gland & seromucinous glands of nasal and oral cavity  Superior salivatory nucleus  nervus intermedius  chorda  joins lingual nerve  submandibular ganglion – postganglioic parasympathteic fibers  submandibular and sublingual glands

20 General Sensory Afferent/Sensory Sensation to auricular concha, EAC wall, part of TM, postauricular skin Cell bodies in geniculate ganglion

21 Special Visceral Afferent/Taste  Postcentral gyrus  nucleus solitarius –> tractus solitarius – nervus intermedius  geniculate ganglion – chorda tympani  joins lingual nerve  anterior 2/3 tongue, soft and hard palate

22 _____

23 Facial nerve blood supply  Intracranial/Meatal: labyrinthine branches from ant inf cerebellar artery  Perigeniculate: superficial petrosal branch of middle meningeal artery  Tympanic/Mastoid: stylomastoid branch of posterior auricular artery

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25 Nerve fiber components  Epineurium – nerve sheath; vasa nervorum  Perineurium – surrounds endoneural tubules; tensile strength, protects against infection  Endoneurium – surrounds axons, adherent to Schwann layer, endoneural tubules regeneration

26 Pathophysiology of nerve injury: Sedon classification  Neuropraxia – conduction blockade from body to distal; distal nerve can still be stimulated. External compress vs intraneural edema  Axonotmesis – wallerian degeneration distal to lesion with preservation of endoneural tubules  Neurotmesis – wallerian degeneration and loss of endoneural tubules/regen layer

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28 Nerve injury

29 Causes of facial paralysis

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31  h/o recurrent alternating facial paralysis  Recurrent orofacial edema (lasts<48 hrs)  chelitis  Fissured tongue  What do I have?

32 HB Facial Nerve Grading

33

34 Topognostic testing  Mainly of historical interest; not prognostic  Uses branching pattern of the facial nerve to identify site of lesion, but is not reliable  Tearing – Schirmer’s test  Stapes reflex – Change in acoustic impedence caused by superthreshold stimulus; stapedial branch of FN is the first efferent branch

35 Auditory testing  To eval for concurrent SNHL or CHL  CHL – middle ear tumors, cholesteatomas, other processes involving tympanic segment  SNHL – acoustic neuromas, meningiomas, congenital cholesteatoma, others involving CPA or IAC

36 Electrophysiologic tests  Measures nerve conduction; from proximal to injury site to muscle/evoked electrical signal.  Cannot measure proximal to stylomastoid foramen  Require waiting until degeneration has progressed enough to be detectable.

37 Nerve stimulation test  NST -office-based, stim main branches with 1 millisec wave pulse, minimal thresholds for facial muslce response are compared  3.5 milliampere difference is pathologic; not sens to lesser degrees of nerve transmission that do not result in loss of visible face motion  Why can’t this test be used during the first 72 hours after injury?

38 Maximal stimulation testing  Variation of NST, but uses maximal stimulation at a level sufficient to depolarize all motor axons under the stimulator  Stim 5 peripheral branches and main trunk  Compares both sides; subj grading  Bell’s – Equal B results up to 10 days, 92% with full recovery. Response lost within 10 days, 100% had incomplete return (May, et al)

39 Electroneuonography ENog/ Evoked electromyography EEMG  Similar to MST except the measured end point is evoked muscle compound action potential amplitudes and latencies (not visible muscle movement); used after 2 weeks of injury  Recording electrodes on nasal alae, stimulator under zygomatic arch

40 EEMG  The peak-to-peak amplitude is proportional to the number of intact motor axons  Example: 10% of normal amplitude = 90% degeneration

41 EEMG - tumor

42 EEMG – Bell’s  Progressive degeneration – 3,4,5 days post-onset  MA = masseter artifact, can be confused with small evoked potential, ID by very short latency

43 Electromyography  Measures activity of muscle (from volitional contraction) instead of the nerve  Measured at insertion, voluntary contraction, at rest  Helps to eliminate false positive NET/MST/EEMG  Diagnostic, not prognostic

44 EMG – insertional, at rest  A – normal needle insertional activity (dec w/ muscular fibrofatty changes)  B – Positive sharp waves (denervation)  C – *Fibrillations (denervation 10-20d)  D – Bizarre formations (myopathies, neuropathies)

45 Motor unit action potential  The motor unit tested by EMG is only a small portion of the muscle fibers in an anatomic motor unit  Motor unit action potential/MUAP is the sum of early discharges of some muscle fibers of one motor unit  Nl MUAP: bi/triphasic, amp mv, duration 3- 16ms

46 EMG  A, inserting needle activity. For suspected muscle atrophy- reanimation usu doesn’t work 2 not enough muscle present.  B. Fibrillation potentials can be seen in conduction block and complete disruption  C. Contracting muscle/smile. Polyphasic potentials indicative of early nerve regenration; polyphasic patterns can be seen in myopathies  D. Recruitment/interference assessed my maximal contraction of a muscle group

47 Limitations of electrophysiologic testing  72 hours delay for MST and EEMG  EMG delay ~14 days until fibrillations seen  Normal variations can be great. EEMG response of 50% have been seen in normal controls.  Must correlate clinical findings with results  Future? Magnetic nerve stimulation for intracranial stim/stim prox to lesion

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49 References  May – The Facial Nerve  Burgess – Reanimation of the Paralyzed Face  Rubin – The Paralyzed face  Netter – Collection of Medical Illustrations, Vol I:Nervous System  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,  Darrouzet, et al. Management of facial paralysis resulting from temporal bone fractures: Our experience ein 115 cases. Otol-Head Neck Surg 125:77-84,  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: , 1987.


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