The Facial Nerve
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The Facial Nerve. NILUBOL TATAYAWONGSAKUL,MD. Anatomy of the facial nerve. 1 . Intracranial. 2 . Intratemporal. 3 . Extratemporal. Anatomy. Intracranial portion. ตั้งแต่ motor cortex จนถึง cerebellopontine angle ก่อนเข้า internal auditory canal. - supranuclear pathway.

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The Facial Nerve

NILUBOL TATAYAWONGSAKUL,MD


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Anatomyof the facial nerve

1. Intracranial

2. Intratemporal

3. Extratemporal


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Anatomy

Intracranialportion

ตั้งแต่ motor cortex จนถึง

cerebellopontine angle

ก่อนเข้า internal auditory canal

- supranuclear pathway

- facial nucleus

- infranuclearpathway


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- contralateral lower face palsy

- upper motor neurone lesion

- lower motor neurone lesion

- ipsilateral whole face palsy


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Intratemporal portion

- meatal segment

- labyrinthine segment

- tympanic or horizontal segment

- mastoid or vertical segment


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Intratemporal portion

Meatal segment อยู่ใน IAC

content ใน IAC ประกอบด้วย facial nerve, cochlear nerve,

superior vestibular nerve, inferior vestibular nerve,

labyrinthine artery

- Bill's bar (crista falciformis)

- Transverse crest.


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Intratemporal portion

Labyrinthine segment

  • from fundus of IAC to

  • geniculate ganglion

  • between labyrinth and cochlear

  • 1st branch - greater superficial

  • petrosal nerve (GSPN)

lacrimal, palatine,

minor salivary gland

- no vascular anastomosis


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Intratemporal portion

Tympanic or horizontal segment

- from genicalate gg to oval window

(1st genu to 2nd genu)

- no branch

-most dehiscence (50%)


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Intratemporal portion

Mastoid or vertical segment

2 nd genu to stylomastoid foramen

- branch to stapedial muscle

- chorda tympani nerve

submandibular, sublingual gland


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Extratemporal or parotid segment

- from stylomastoid foramen เข้าสู่ parotid gland

แบ่งเป็น superficial and deep lobe

แตกแขนงมีลักษณะเป็น pes ancerinus (goose's foot)


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Function of the facial nerve between mastoid tip – EAC

1. Special visceral afferent (SVA)

2. General visceral afferent (GVA)

3. Special visceral efferent (SVE)

4. General visceral efferent (GVE)


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1 between mastoid tip – EAC . Special visceral afferent (SVA)

taste fiber (taste bud ant r 2/3 of tongue, hard and soft palate)

geniculate gg

chorda tympani (lingual nerve)

nervus intermedius

nucleus of tractus solitareus


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2 between mastoid tip – EAC . General visceral afferent (GVA)

sensory fibers (tympanic cavity, tympanic membrane, EAC)

nucleus of tractus solitareus


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3 between mastoid tip – EAC . Special visceral efferent (SVE)

motor fiber

muscles of facial expression, platysma m.,

posterior belly of digastric m, stylohyoid m.


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4 between mastoid tip – EAC . General visceral efferent (GVE)

parasympathetic fiber

จาก superior salivary nucleus

lacrimal, palatine, minor salivary gland (GSPN)

submandibular, sublingual gland (chorda tympani n.)


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Pathophysiology between mastoid tip – EAC of peripheral nerve lesion

Sunderland classification

1st degree (neurapraxia)

2nd degree (axonotemesis)

3rd degree

4th degree

neurotemesis

5th degree


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Sunderland classification between mastoid tip – EAC

1st degree (neurapraxia) =compression ทุกอย่างยังดี

2nd degree (axonotemesis) = wallerian degeneration

neurotemesis

3rd degree = axon + endoneurium ขาด

4th degree= axon + endoneurium + perineurium ขาด

5th degree = axon + endoneurium + perineurium

+ epineurium ขาด


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House-Brackmann System of grading between mastoid tip – EAC

facial nerve recovery


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House-Brackmann System of grading between mastoid tip – EAC

facial nerve recovery


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Regeneration of nerve injury between mastoid tip – EAC

Electrical testing can distinguish class I from class II to V lesions

but cannot distinguish class II from class V


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Special facial nerve test between mastoid tip – EAC

- Topographic test

- Prognostic test or Electrical test


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Topographic test between mastoid tip – EAC

- Location of facial nerve injury

  • Test branch of facial nerve

    • Lacrimation

    • Salivation

    • Taste

    • Stapidius reflex

ได้ผลค่อนข้างถูกต้องในราย temporal bone fracture

(complete focal lesion)

แต่ใน Bell’s palsy จะเชื่อถือได้น้อย(partial lesion with

varying degree of conductive block)


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Topographic test between mastoid tip – EAC

1. Lacrimation test=Schirmer’s test


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Topographic test between mastoid tip – EAC

2. Stapedial reflex test


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Topographic test between mastoid tip – EAC

3.Taste test (electrogustometry)


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Topographic test between mastoid tip – EAC

4.Salivary flow test


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Topographic test between mastoid tip – EAC 5.Salivary PH

  • Normal: PH .>,= 6.4

  • PH < 6.1= incomplete recovery in case of Bell’s palsy

  • Accuracy prediction = 91%

  • Unknown cause this test

  • Give an earier prognosis than other test


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Prognostic test or Electrical test between mastoid tip – EAC

  • severity of axonal degeneration

  • Require serial testing

  • Compared with the normal side

  • ใช้access motor function of facial n. at distal to stylomastoid foramen

  • กรณีlesionที่ proximal กว่าตำแหน่ง test ต้องรอ wallerian degeneration ก่อน test ซึ่งใช้เวลาอย่างน้อย 72 ชั่วโมง(Not determine in the immediate post injury stete)


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Electrical test between mastoid tip – EAC

7 test

  • Nerve excitability test (NET) or Hilger's test

  • Maximum stimulation test

  • Electroneuronography (ENOG)

  • Evoked Electromyography (EEMG)

  • Electromyography (EMG

  • Magnetic stimulation

  • Facial Nerve Monitoring


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Nerve excitability test (NET) or Hilger's test between mastoid tip – EAC

  • ใช้ DC current กระตุ้น nerve trunk นาน 0.3msec. เปรียบเทียบ muscle contraction 2 side

  • ทำหลัง onset 3 day

  • มักทำ marginal mandibular branch เพราะตื้นที่สุด

  • Stimulating electrode is place on skin over stylomastiod foramen or over one of peripheral branch of the nerve


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Frontal branch - 1 inch lateral to outer canthus between mastoid tip – EAC

Zygomatic branch - bony lateral border of orbit

ant r to the point that facial a.

pass mandible

Marginal mandibular branch –


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Nerve excitability test (NET) or Hilger's test between mastoid tip – EAC

  • minimum electrical stimulation

  • > 6mA in injury side

- different > 3.5 m A

Severe degeneration


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NET between mastoid tip – EAC

  • เมื่อใช้ NET different >3.5 เป็น criteria ในการทำการผ่าตัด nerve decompression จะมี accuracy 80%

  • มีประโยชน์เฉพาะ(Useful only) first 2-3 weeks of complete paralysis,before complete degeneration has occure

  • ใน incomplete paralysis จะมี normal response เมื่อกระตุ้น distal ต่อ pathologic site จึงไม่ควรทำ NET ใน incomplete paralysis

  • Clinical recovery จะมาก่อน NET recovery จึงไม่มีประโยชน์ในการ F/U NET


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Maximum stimulation test between mastoid tip – EAC (MST)

  • กระตุ้นด้วย maximal DC current ที่ผู้ป่วยทนได้(5mA) จนเห็น maximal movement

  • เริ่มทำในข้างที่ดีก่อนแล้วทำข้างเสีย เปรียบเทียบเป็น % กับข้างดี

  • Stimulate all intact axon,ประเมินสัดส่วนของ fiber ที่ degenerate ฉะนั้นจึงให้information more reliably guide prognosis and treatment than NET

(full muscle contraction or pain)

  • result - equal 100%, mild 75%, moderate 50%,

  • severe 25%, complete 0%

- ถ้า severe (<25%)

75% incomplete recovery


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  • Bell’s palsy between mastoid tip – EAC ถ้าพบ

    • Normal MST 88% = complete recovery

    • Absence of electrically stimulated movement asso. C incomplete recovery


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Electroneuronography between mastoid tip – EAC (ENOG)

Evoked Electromyography (EEMG)

  • หลักการเหมือน MST แต่ recod เป็นกราฟ

  • Electrical summation potential

  • เป็น objective test

  • เป็น most acceptable for

  • prognostic indicator

- เปรียบเทียบ compound action potential (CAP) กับข้างดี


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  • Normal between mastoid tip – EAC ต่างกันน้อยกว่า 3%

  • อาจมี Test error 20%

  • 0-50% degeneration : good prognostic indicator

  • 50-90% degeneration : fair recovery

  • >90% degeneration : poor recovery (surgery is indicate in traumatic)

  • ปัจจุบันใช้ 95% degenertion ( =5% normal site)เป็น surgical indication ใน Bell’palsy (เพราะ ใน 2 wk. จะมี 50% change of poor recovery)


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ทั้ง between mastoid tip – EAC NET, MST, ENOG

จะทดสอบได้ก็ต่อเมื่อมี axon degeneration ก่อน

ซึ่งจะเกิดขึ้น 48-72 ชม. หลัง injury

เพราะฉะนั้นตรวจและแปลผลได้ เมื่อเกิน 72 ชม. ไปแล้ว


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Electromyography between mastoid tip – EAC (EMG)

  • ใช้ evaluate the motor unit

  • ใช้ electrode วัด electrical activity

  • Recoding of spontaneous and voluntary muscle potential by needle introduced into the muscle


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Electromyography between mastoid tip – EAC (EMG)

Muscle electrical response at rest and contraction

Normal

- needle insertion

- muscle contraction

- rest

- no muscle activity

- contraction

- muscle activity (CAP)

Degeneration

- fibrillation wave

- at rest

- no muscle activity

- contraction

พบประมาณ 2 สัปดาห์ หลัง injury


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  • แปรผล between mastoid tip – EAC

    • Biphasic or triphasic = normal motor unit

    • Fibrillation = degeneration (อาจพบได้ตั้งแต่ 10-14 วัน หลังinjury ซึ่งยืนยันว่ามี degeneration จริง

    • Polyphasic สำคัญ ใช้บอก = regeneration = reinnervation (4-6 weeks after the onset of the paralysis)


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Magnetic stimulation between mastoid tip – EAC

- กระตุ้น facial nerve ตั้งแต่บริเวณ geniculate ganglion,

internal auditory canal โดยตรง

  • ข้อดี 2 ข้อ

  • ทดสอบได้เร็วตั้งแต่เริ่มมี injury , บ่งตำแหน่งรอยโรคได้,

  • test up 4 days after on set of Bell’s palsy

  • without pain and discomfort

- ยังอยู่ระหว่างการศึกษาถึงประโยชน์ที่ชัดเจน


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Facial Nerve Monitoring between mastoid tip – EAC

  • Intra-operative monitoring

    • Audible EMG(needle or surface electrode, monopolar or bipolar stimulation)

    • At the end of the case the nerve can be stimulated successfully near the brainstem with low currents (0.05-0.1mA), the prognosis for postoperative function is excellent


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Thank you between mastoid tip – EAC


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