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TRAUMATIC FACIAL PALSY — Causes & Management

(50 Marks | RGUHS Standard)

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PART I: INTRODUCTION

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PART II: SURGICAL ANATOMY OF THE FACIAL NERVE

Segments of the Facial Nerve (Intratemporal)

BRAINSTEM (Pons — motor nucleus)
    ↓
CISTERNAL SEGMENT (in posterior fossa)
    ↓
MEATAL SEGMENT (Internal Auditory Canal — ~8 mm)
    ↓
LABYRINTHINE SEGMENT (3–4 mm — NARROWEST, most vulnerable)
    ↓ Geniculate ganglion (gives off Greater Petrosal Nerve → parasympathetics)
TYMPANIC / HORIZONTAL SEGMENT (8–11 mm — medial wall of middle ear)
    ↓ Stapedius nerve
MASTOID / VERTICAL SEGMENT (10–14 mm — descends in posterior mastoid)
    ↓ Chorda tympani (taste, submandibular/sublingual glands)
STYLOMASTOID FORAMEN (exits skull base)
    ↓
EXTRATEMPORAL (parotid gland → pes anserinus → 5 peripheral branches)
       ┌──────────────────────────────────────┐
    Temporal  Zygomatic  Buccal  Marginal  Cervical

• The labyrinthine segment has the smallest cross-sectional diameter and the narrowest bony canal — hence most susceptible to oedema and compression
• The geniculate ganglion is the most common site of injury in temporal bone fractures
• The nerve is dehiscent in up to 55% of normal temporal bones in the tympanic segment — a risk factor for inflammatory palsy and surgical injury

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PART III: CAUSES OF TRAUMATIC FACIAL PALSY

CLASSIFICATION

TRAUMATIC FACIAL PALSY
├── A. BLUNT TRAUMA
│   ├── 1. Temporal Bone Fractures
│   │   ├── Longitudinal
│   │   ├── Transverse
│   │   ├── Mixed/Oblique
│   │   └── Otic Capsule Disrupting / Sparing
│   └── 2. Birth Trauma
│
├── B. PENETRATING TRAUMA
│   ├── 3. Gunshot/Blast injuries
│   ├── 4. Stab wounds / sharp facial lacerations
│   └── 5. Foreign body injuries
│
├── C. IATROGENIC TRAUMA
│   ├── 6. Parotid surgery
│   ├── 7. Mastoid & middle ear surgery
│   ├── 8. Skull base surgery
│   ├── 9. Neck dissection
│   ├── 10. Facelift / rhytidectomy
│   └── 11. Dental injections (inferior alveolar nerve block)
│
└── D. BIRTH TRAUMA
    └── 12. Forceps delivery

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A. TEMPORAL BONE FRACTURES (Most Common Cause)

TRADITIONAL CLASSIFICATION

MODERN CLASSIFICATION (Preferred — based on otic capsule involvement)

• Associated with facial nerve injury in 30–50% of cases
• SNHL, vestibular dysfunction
• Higher medico-legal significance

• Facial palsy in 10%
• Conductive hearing loss more common

MECHANISMS OF INJURY IN TEMPORAL BONE FRACTURES

1. Direct compression by bone fragment impinging on the nerve
2. Intratemporal haematoma causing pressure necrosis
3. Entrapment from bony compression in the fallopian canal
4. Loss of continuity — complete transection (rare, ~5%)
5. Oedema and demyelination — most common; similar histology to Bell's palsy (Grobman et al.)
6. Devascularisation — disruption of vasa nervorum
7. Traction injury — at the geniculate ganglion, caused by counter-distraction of anterior and posterior temporal bone fragments

• Narrowest cross-sectional diameter in the fallopian canal
• Lacks fibrous supporting tissue
• Traction stress between Greater Petrosal Nerve and geniculate ganglion

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B. PENETRATING INJURIES

• Most severe form of facial nerve injury
• Causes loss of continuity in majority
• Complex trajectory; bone is often comminuted
• Requires surgical exploration in nearly all complete palsies

• Extratemporal facial nerve branches
• Any branch peripheral to the parotid may be divided
• Posterior to a vertical line through the lateral canthus — branches large enough to repair primarily

• Blast injuries with penetrating shrapnel
• Industrial accidents

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C. IATROGENIC INJURY

1. Parotid Surgery

• Most feared complication of parotidectomy
• Temporary palsy — 15–20% of superficial parotidectomies; resolves in weeks to months
• Permanent palsy — 1–2%
• Marginal mandibular and frontal branches most at risk
• Causes: excessive retraction, thermal injury from electrocautery, devascularisation, inadvertent division

2. Middle Ear & Mastoid Surgery

• Risk highest during:
  • Canal wall down mastoidectomy (posterior genu)
  • Stapedectomy (horizontal segment dehiscence)
  • Tympanoplasty
• Cholesteatoma — may erode fallopian canal, making nerve vulnerable
• Prompt recognition: if discovered intraoperatively → decompress and administer steroids

3. Skull Base Surgery

• Acoustic neuroma (vestibular schwannoma) resection — FN is at greatest risk
• Jugular foramen tumour surgery
• Middle and posterior cranial fossa approaches

4. Neck Dissection

• Marginal mandibular branch at risk during ligation of facial vein
• Retromandibular vein is a surgical landmark

5. Facelift (Rhytidectomy)

• Temporal and zygomatic branches at risk in SMAS plane dissection
• Frontal branch — at risk crossing zygomatic arch

6. Dental Injections

• Inferior alveolar nerve block — accidental injection into parotid
• Causes temporary (1–3 hours) ipsilateral facial weakness
• No treatment needed

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D. BIRTH TRAUMA

• Forceps delivery → compression of facial nerve at stylomastoid foramen (nerve superficial in neonates, no mastoid tip protection)
• Incidence: ~0.25% of forceps deliveries
• Usually incomplete palsy; nearly always recovers spontaneously
• Must be distinguished from Möbius syndrome (congenital bilateral FN agenesis/aplasia)

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PART IV: CLINICAL EVALUATION

History

• Onset: Immediate vs. Delayed
  • Immediate → direct structural injury (nerve transection/compression by bony fragment)
  • Delayed → oedema/haematoma with evolving neurapraxia; better prognosis
• Mechanism and severity of trauma
• LOC, associated neurological deficit
• Previous medications (paralytic agents may mask early assessment)

Physical Examination

• Full HB grading
• Eye closure, brow movement, nasolabial fold, corner of mouth
• Associated features: hemotympanum, CSF otorrhea (otorrhagia), Battle's sign, raccoon eyes
• Tuning fork tests, otoscopy
• Check for nystagmus (labyrinthine involvement)
• Note: "Differentiation of delayed onset from delayed diagnosis is crucial" — Cummings

Topognostic Tests (Localisation of Lesion Site)

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PART V: INVESTIGATIONS

A. Electrodiagnostic Tests

1. Electroneuronography (ENoG) — MOST IMPORTANT

• Stimulates facial nerve at stylomastoid foramen; records compound muscle action potential (CMAP)
• Compares amplitude of affected vs. normal side
• >90% degeneration within 6 days = criterion for surgery (Fisch's criterion)
• Most useful Days 3–21 after injury (wallerian degeneration needs 72 hours)
• Not valid in long-standing paralysis

2. Electromyography (EMG)

• Detects voluntary motor unit potentials (MUPs) — indicates viable axons
• Fibrillation potentials = denervation (appear 10–14 days after injury)
• Polyphasic reinnervation potentials = recovery (appear before clinical improvement)
• Useful for: long-standing paralysis, monitoring recovery

3. Maximum Stimulation Test (MST) / Nerve Excitability Test (NET)

• Older, less quantitative
• NET: Minimum current required for visible muscle twitch
  • Difference >3.5 mA suggests significant degeneration
• MST: Maximum current stimulation — no visible response = poor prognosis

B. Imaging

High-Resolution CT (HRCT) of Temporal Bone — GOLD STANDARD

• Axial and coronal cuts at 0.5 mm slices
• Identifies:
  • Fracture lines through fallopian canal
  • Widening/narrowing of the canal
  • Displaced bone fragments
  • Otic capsule involvement

• Most accurate at: geniculate ganglion and labyrinthine segment
• Underestimates: mastoid and pyramid segment injuries
• Most intraoperative findings show nerve oedema, not transection

MRI

• Gadolinium-enhanced MRI: enhancement of facial nerve = oedema/inflammation
• Role: when HRCT inconclusive; to evaluate intracranial extension or soft tissue injury
• Not first-line in acute trauma

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PART VI: MANAGEMENT

MANAGEMENT FLOWCHART

TRAUMATIC FACIAL PALSY DIAGNOSED
          |
          ▼
ASSESS ONSET OF PARALYSIS
          |
    ┌─────┴───────┐
IMMEDIATE          DELAYED
onset              onset
    |                  |
    ▼                  ▼
HIGH-RESOLUTION CT    CONSERVATIVE
TEMPORAL BONE         (steroids +
+ ENoG               eye care)
    |                  |
Fracture    No           |         Spontaneous
through     fracture  Worsening?   recovery?
FN canal    on CT     (ENoG >90%  → OBSERVE
    |        |         in 6 days)     & MONITOR
    |        ▼              |           with EMG
    |    Conservative   YES
    |    Management      |
    |                    ▼
    └────────────→  SURGICAL EXPLORATION
                           |
              ┌────────────┼─────────────────┐
              ▼            ▼                  ▼
         Nerve intact   Nerve compressed    Nerve
         (oedema only)  by bone/haematoma   DIVIDED
              |              |                |
          Decompress    Remove bony       ┌───┴────┐
          fallopian     fragments +   <3cm gap   >3cm gap
          canal         decompress        |           |
              |              |        Primary end-  Cable graft
              ▼              ▼        to-end repair  (sural n./
           CLOSE         DECOMPRESS   (epineural)   GAN/ANSA)

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A. NON-OPERATIVE (CONSERVATIVE) MANAGEMENT

1. Delayed-onset facial palsy (most recover spontaneously)
2. Incomplete paralysis (any grade) — virtually always recovers
3. Immediate-onset palsy with <90% degeneration on ENoG
4. Patient unfit for surgery

Conservative Management Protocol

• Reduce intratemporal oedema
• Prednisolone 1 mg/kg/day (max 60 mg) × 7–10 days, then taper
• Initiated as soon as safely possible
• Contraindicated if severe head injury / raised ICP

• Artificial tear drops — every 2 hours when awake
• Lubricating eye ointment at night
• Protective spectacles / moisture chamber glasses
• Taping the eye shut at night (micropore / Tegaderm)
• If grade V–VI: temporary tarsoraphy or gold weight implant (upper eyelid)

• Biofeedback-assisted facial retraining
• Neuromuscular re-education
• Massage of facial muscles
• Begin once reinnervation potentials appear on EMG

• Serial ENoG at 3, 6, and 14 days
• If <90% degeneration at 6 days → continue conservative management
• If >90% degeneration at 6 days → reconsider surgical decompression

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B. SURGICAL MANAGEMENT

INDICATIONS FOR SURGERY (Cummings, Fisch criteria)

TIMING OF SURGERY

• For immediate-onset complete palsy: Surgery within 2–3 weeks preferred
• Delaying up to 3 weeks may be advantageous — allows resolution of oedema/haematoma, making surgical field clearer
• For long-standing paralysis: Explore at 12 months if no recovery on EMG
• In penetrating injuries: Explore as soon as medically stable (within days)

SURGICAL APPROACHES

SITE OF INJURY ON HRCT/ENoG
          |
   ┌──────┴───────────────┐
Labyrinthine/         Mastoid/
Geniculate/           Tympanic
Tympanic segment      segment
   |                       |
MIDDLE CRANIAL         TRANSMASTOID
FOSSA APPROACH         ±
(if hearing              POSTERIOR TYMPANOTOMY
preserved)
   |                       |
   └──────────┬────────────┘
              ▼
       COMBINED APPROACH
    (Middle Cranial Fossa +
     Transmastoid/
     Translabyrinthine)
     — when hearing lost —

• For mastoid segment (vertical) injuries
• Also allows access to tympanic segment via posterior tympanotomy
• Decompresses nerve from second genu to stylomastoid foramen

• For labyrinthine segment and geniculate ganglion injuries
• Hearing preservation approach
• Technically demanding; requires neurotological expertise
• Risks: temporal lobe retraction, CSF leak, epidural haematoma

• When hearing is already destroyed (e.g., transverse fracture with SNHL)
• Excellent access to entire intratemporal segment
• Sacrifices cochlea/vestibule
• Least risk to brain

INTRAOPERATIVE MANAGEMENT

• For oedema/haematoma without nerve transection
• Remove bone of fallopian canal with diamond burr for 270° circumference
• Slit the epineurium (epineuriotomy) to release intraneural pressure
• "Approach from proximal and distal uninvolved segments toward diseased area" (Cummings)
• Use flat, blunt instruments to dissect granulation tissue from nerve
• Avoid sharp dissection at epineurium unless absolutely necessary

• For transected nerve with gap <3 mm (after freshening ends)
• Tension-free anastomosis essential
• Epineural repair — suturing epineurium, 8-0 or 9-0 nylon/prolene
• Best results if performed within 72 hours of injury (acute repair) or after minimal delay

• For gaps >3 mm after transection
• Donor nerves:
  • Greater Auricular Nerve (GAN) — most commonly used; provides ~7 cm; harvested from neck
  • Sural Nerve — provides up to 30–40 cm; used for longer defects
  • Ansa cervicalis
  • Medial cutaneous nerve of forearm
• Graft is reversed (to avoid axonal escape at branches)
• Anastomosed epineurially at each end
• Expected recovery: HB Grade III in 60–70% of patients

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C. MANAGEMENT OF LONG-STANDING/ESTABLISHED PALSY

Static Procedures (Immediate symmetry at rest)

1. Fascial sling — tensor fascia lata sling to angle of mouth
2. Brow lift — frontalis sling or brow suspension
3. Gold weight implant (upper eyelid) — for lagophthalmos; 0.6–1.6 g
4. Lower eyelid tightening — lateral tarsal strip
5. Tarsoraphy — temporary or permanent

Dynamic Procedures (Restore voluntary movement)

1. Nerve substitution (XII–VII anastomosis)
   • Hypoglossal–facial nerve anastomosis
   • Provides resting tone and bulk to face
   • Tongue hemiatrophy is major drawback
   • Partial XII–VII: splits hypoglossal nerve — reduces morbidity
2. Cross-facial nerve graft (CFNG)
   • Sural nerve graft tunnelled across face
   • Takes axons from contralateral healthy VII branches
   • Allows spontaneous, emotive facial movement
   • Takes 9–12 months for axonal growth; two-stage procedure
3. Microneurovascular free muscle transfer (gold standard for long-standing)
   • Gracilis free flap with obturator nerve anastomosed to CFNG or masseter nerve
   • Provides true voluntary and spontaneous movement
   • Can be powered by masseter nerve (single-stage) or CFNG (two-stage)
4. Temporalis muscle transposition (modified Gillies procedure)
   • Temporalis muscle slip rotated and attached to angle of mouth
   • Utilises trigeminal (V) nerve input
   • Simple, reliable, no microsurgery
   • Drawback: requires deliberate jaw-clenching for movement (synkinesis)
5. Masseter–facial nerve anastomosis (V–VII)
   • Masseteric branch of V3 anastomosed to main trunk or buccal branch
   • Strong reinnervation; minimal donor defect
   • Patient learns to clench jaw for facial movement
   • Recent advance: Combination of masseteric nerve + CFNG (babysitter procedure)

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D. EYE MANAGEMENT IN DETAIL

LAGOPHTHALMOS ASSESSMENT
          |
    ┌─────┴───────┐
  <3mm gap       >3mm gap
  at gentle      or poor Bell's
  closure        phenomenon
    |                  |
  Lubricants     Add moisture
  q2h            chamber + night
                 taping
                    |
              No improvement /
              permanent palsy
                    |
              ┌─────┴───────┐
          Temporary       Permanent
          tarsoraphy      gold weight
          (reversible)    implant +
                          lower lid
                          tightening

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PART VII: ALGORITHM — COMPLETE MANAGEMENT SUMMARY

TRAUMA → FACIAL WEAKNESS DETECTED
              ↓
    IMMEDIATE HISTORY & EXAMINATION
    (HB Grade, mechanism, onset timing)
              ↓
     HRCT TEMPORAL BONE (axial + coronal)
              ↓
    ┌─────────┴──────────┐
INCOMPLETE              COMPLETE PALSY
PALSY                   (HB V–VI)
    |                       |
Conservative           Determine ONSET
(steroids,             (Immediate vs Delayed)
eye care)                   |
    |                ┌──────┴──────────┐
Monitor              IMMEDIATE         DELAYED
with ENoG            (day 0)           (>24 hrs)
                         |                  |
                    ENoG Day 3–6       Conservative
                         |             (steroids, serial
                 <90% deg. >90% deg.   ENoG monitoring)
                         |       |          |
                   Continue    SURGERY   Worsens to
                   conservative          >90% ENoG?
                                              |
                                       CONSIDER SURGERY
                                              |
                              ┌───────────────┼────────────────┐
                           Intact          Compressed        Transected
                           nerve           nerve              nerve
                           (oedema)        (fragment/         (<3mm gap vs
                                           haematoma)         >3mm gap)
                              |                |                    |
                         Decompress      Remove fragments      Primary repair
                         fallopian       + Decompress          vs Cable graft
                         canal                                 (GAN/Sural)
                              ↓
                    POST-OP EYE CARE + FACIAL REHABILITATION

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PART VIII: RECENT ADVANCES

1. Intraoperative Facial Nerve Monitoring (IONM)

• Continuous EMG monitoring of facial muscles during temporal bone/skull base surgery
• Reduces iatrogenic injury significantly
• Alert surgeon to proximity of the nerve
• Real-time neurotonic discharges indicate mechanical irritation

2. Robot-Assisted Surgery

• Robotic systems (da Vinci) allow precision in parotid surgery, reducing iatrogenic FNP
• Minimally invasive approach to parotid lesions — currently in trials

3. Gabapentin / Pregabalin in Neuropathic Pain

• Post-traumatic synkinesis and aberrant regeneration pain management
• Used alongside botulinum toxin therapy

4. Botulinum Toxin Type A (BTX-A)

• Management of synkinesis after recovery (aberrant reinnervation)
• Also used to balance the contralateral hyperactive face in longstanding palsy
• Injected into hyperactive muscles (orbicularis, mentalis, platysma)

5. Masseteric Nerve (Motor Branch of V3) — "Babysitter Procedure"

• Rapid reinnervation of the facial musculature
• Combining masseteric nerve with cross-facial nerve graft allows both early reinnervation AND spontaneous emotional movement
• Published by Biglioli et al., Terzis & Olivares — becoming gold standard in paralysis >2 years

6. Selective Neurectomy for Synkinesis

• Division of nerve branches causing involuntary movements
• Combined with BTX-A and physical therapy

7. Regenerative Medicine & Nerve Conduits

• Biodegradable nerve conduits (collagen, polyglycolic acid) for nerve gaps
• Growth factor delivery (BDNF, NGF) to enhance axonal regeneration
• Stem cell-seeded scaffolds — experimental

8. 3D Printing in Facial Reanimation

• Custom-fabricated static slings
• Patient-specific implants for facial symmetry

9. Validated Outcome Tools

• eFACE (electronic, clinician-rated)
• FACE-Q (patient-reported outcomes)
• Sunnybrook Facial Grading System — regional scoring with synkinesis assessment
• Replacing the older, less sensitive HB scale in research settings

10. Diffusion Tensor Imaging (DTI-MRI)

• Tractography of the facial nerve in the temporal bone
• Allows pre-surgical mapping without radiation
• Still investigational; promising for planning decompression

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PART IX: PROGNOSIS

• Incomplete palsy → virtually 100% complete recovery
• Complete delayed-onset palsy → >90% good recovery (HB I–II)
• Complete immediate-onset palsy → ~50% full recovery without surgery; up to 70% with timely decompression

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PART X: KEY REFERENCES

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SUMMARY TABLE

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