Facial Nerve

Prof. Dr. Norberto V. Martinez

Faculty of Medicine and Surgery

University of Santo Tomas

Six Anatomical Segments

• Intracranial

• Meatal

• Labyrinthine

• Tympanic

• Mastoid

• extratemporal

Facial Nerve Surgery & Decompression

4 functional components

• Motor nucleus (efferent)• Parasympathetic fibers-greater superficial

petrosal nerve & chorda tympani ( Nervus Intermedius)

• Special Visceral Afferent from Nucleus Tractus Solitarius(afferent)

• General Sensory Afferent-cutaneous sensation to external ear & postauricular area (afferent)

Supra nuclear pathway

• Motor function origin begins at cerebral cortex

• Primary somatomotor cortex in the precentral gyrus (brodmann area4,6,8)

Facial Nucleus and Brainstem

• Facial nucleus lies within the reticular formation at the lower level of the pons

• There is distinctly ipsi & contalateral cortical input within the facial nucleus

superior or ventral – receives bilateral input

inferior or dorsal – receives contralateral input

INTERNAL AUDITORY CANAL(meatal)

• Traverse crest divides IAC into superior and inferior

• Superior portionfacial nerve anteriorly superior vestibular nerve posteriorly

• Inferior portion cochlear nerve anteriorlyinferior vestibular nerve posteriorly

FALLOPIAN CANAL

• Facial canal is approximately 30 mm long

• From Bills bar up to the stylomastoid foramen

• 3 intratemporal regionlabyrinthinetympanic mastoid

Labyrinthine segment

• Shortest segment (3-4mm)• Lies between labyrinth and cochlea • Beginning from fundus of IAC extending upto

geniculate ganglion*• Narrowest portion of fallopian canal is the

meatal foramen (junction bet IAC and Labyrinthine segment)• Labrynthine segment terminates in the

genicultae ganglion and will make a 40 to 80 turn(1st genu)

Mastoid Segment

• From 2nd genu to stylomastoid foramen

• Descends inferiorly and becomes more lateral *

• 2 branches- nerve to stapedius and chorda tympani

• Angle between chorda tympani and vertical portion is 30 degrees(facial recess)

Extra Temporal Segment

• 3 minor branches after leaving the stylomastoid foramen

• post auricular nervebranch to digastric musclestylohyoid muscle

• Further arborization occurs with frequent anastomosis occurs in the intraparotid course

• Five classic branches- temporal,zygomatic,buccal,mandibular,cervical

Blood Supply

• Blood supply is segmented derived from 3 arterial sources Nager 1953

brainstem to IAC: AICA

perigeniculate segment: Mid. meningeal artery

mastoid –tympanic: stylomastoid branch of post auricular artery

House Brackmann Facial Nerve Grading System

I. Normal• Normal facial function in all areas

House Brackmann Facial Nerve Grading System

II. Mild Dysfunction• Gross

– Slight weakness noticeable in close inspection . May have very slight synkinesis. At rest normal symmetry and tone.

• Motion– Forehead: moderate to good function– Eye: complete closure with minimal effort – Mouth: slight assymetry

House Brackmann Facial Nerve Grading System

III. Moderate Dysfunction• Gross

– Obvious, but not disfiguring difference between the two sides. Noticeable but not severe synkinesis, contracture, or hemifacial spasm. At rest, normal symmetry and tone.

• Motion– Forehead: slight to moderate movement– Eye: complete closure with effort– Mouth: slightly weak with maximum effort

House Brackmann Facial Nerve Grading System

IV. Moderately severe Dysfunction• Gross

– Obvious weakness and/or disfiguring assymetry. At rest, normal symmetry and tone.

• Motion– Forehead: none– Eye: incomplete closure– Mouth: assymetric with maximum effort

House Brackmann Facial Nerve Grading System

V. Severe Dysfunction• Gross

– Only barely perceptible motion• Motion

– Forehead: none– Eye: incomplete closure– Mouth: slight movement

House Brackmann Facial Nerve Grading System

VI. Total Paralysis• No movement

ELECTROPHYSIOLOGIC TESTING

1. Nerve Excitability Test

2. Maximal stimulation test

3. Electroneurography

4. Electromyography

• Electrical excitability test percutaneous stimulation of the facial nerve until muscle contraction is observed.

Electroneurography (ENoG)

Electroneurography (ENoG)

ENoG - Normal ENoG - Paralysis

Electromyography (EMG)

EMG – Normal

EMG – fibrillation potentials

Electromyography (EMG)

Electromyography (EMG)

EMG – polyphasic neurogenic potential

Facial Nerve InjuryIncidence

1% - Primary Otological Surgery

4 – 10% - Revision Cases

Primary Reason:

• 80% lack of familiarity with surgical anatomy

• Tear of Facial Nerve

• High facial ridge in CWD

Management Protocol

1. Complete post-op palsy• Immediate re-exploration• Decompression• Re-approximation severely

damaged• Interposition grafting loss of neural

tissue

Management Protocol

2. Delayed onset observation

Hilger minimal stimulation test after 72

hours, if (-) response at 5 mA ENOG >80 % neural degenerationExplore & decompression

Transmastoid Decompression

Thank You!