FACIAL NERVE PALSY: CAUSES AND MANAGEMENT FOLLOWING MASTOIDECTOMY

A Comprehensive RGUHS 50-Marks Answer

PART A: CAUSES OF FACIAL NERVE PALSY

Classification of Causes

I. ANATOMICAL CLASSIFICATION

┌─────────────────────────────────────────────────────┐
│           FACIAL NERVE PALSY – CLASSIFICATION        │
│                  BY SITE OF LESION                   │
├─────────────────────────────────────────────────────┤
│  SUPRANUCLEAR (UMN)                                  │
│    ├─ Stroke, tumor, abscess (contralateral)         │
│    └─ Forehead SPARED (bilateral supranuclear        │
│        input to upper face)                          │
├─────────────────────────────────────────────────────┤
│  NUCLEAR (PONTINE)                                   │
│    ├─ Ipsilateral LMN palsy + VI nerve palsy         │
│    ├─ Tumors, demyelination, infarction              │
│    └─ Millard–Gubler syndrome                       │
├─────────────────────────────────────────────────────┤
│  INFRANUCLEAR (PERIPHERAL / LMN)                     │
│    ├─ Intracranial (CPA/IAC)                         │
│    ├─ Intratemporal (within petrous bone)            │
│    └─ Extratemporal (parotid, face)                  │
└─────────────────────────────────────────────────────┘

II. ETIOLOGICAL CLASSIFICATION (Mnemonic: INTIVTM)

DETAILED CAUSES

1. Bell's Palsy (Idiopathic)

• Most common cause; accounts for 60–70% of all facial palsies
• Viral aetiology — Herpes simplex virus type 1 (HSV-1) reactivation in the geniculate ganglion
• Acute, unilateral, LMN type; rapid onset (<72 hours)
• Diagnosis of exclusion
• — Schwartz's Principles of Surgery, p. 643

2. Ramsay Hunt Syndrome (Herpes Zoster Oticus)

• Varicella zoster virus (VZV) reactivation from geniculate ganglion
• Triad: Otalgia + auricular vesicles + facial palsy
• May involve VIII nerve → sensorineural hearing loss, vertigo
• Prognosis worse than Bell's palsy; complete recovery in only ~66%
• — Schwartz's Principles of Surgery, p. 643

3. Otogenic Causes

• Acute Otitis Media (AOM): Inflammatory/infective involvement via dehiscent facial canal (20% incidence of dehiscence — Cummings)
• Chronic Suppurative Otitis Media (CSOM) with Cholesteatoma: Bone erosion of the fallopian canal (most commonly tympanic segment overlying oval window)
• Cholesteatoma-related facial palsy = emergency requiring urgent surgery

4. Traumatic (Iatrogenic – Post-Mastoidectomy)

• Most common surgical site: Vertical (mastoid) segment
• Occurs at:
  • Descending (vertical) segment — most common
  • Tympanic segment — especially near oval window (dehiscence 20%)
  • Geniculate ganglion

5. Neoplastic

• Facial neuroma — slowly progressive palsy; twitching + weakness suggestive
• Glomus jugulare/tympanicum — pulsatile tinnitus, hearing loss
• Parotid malignancy — extratemporal segment
• Vestibular schwannoma (acoustic neuroma) — IAC/CPA; facial weakness rare but possible in large tumours

6. Traumatic (Temporal Bone Fracture)

• Transverse fracture — passes through IAC/labyrinth; facial palsy common (50%), immediate
• Longitudinal fracture — more common (80%); facial palsy in 20%, often delayed

7. Systemic/Autoimmune

• Sarcoidosis (Heerfordt's syndrome): Uveitis + parotitis + fever + bilateral facial palsy
• Melkersson–Rosenthal syndrome: Recurrent facial palsy + orofacial oedema + fissured tongue
• Lyme disease (Borrelia burgdorferi)
• Multiple sclerosis
• Diabetes mellitus

8. Congenital

• Möbius syndrome (CN VI + VII bilateral)
• Birth trauma (forceps injury, sacral pressure)
• CHARGE syndrome
• Hemifacial microsomia

PART B: MANAGEMENT OF FACIAL NERVE PALSY FOLLOWING MASTOIDECTOMY

INTRODUCTION

INCIDENCE

• Reported incidence of facial nerve injury during mastoidectomy: 0.5–3.6%
• Dehiscence of facial canal in cholesteatoma cases: ~20% (Cummings)
• Most common site of injury: tympanic segment (overlying oval window) and descending mastoid segment

MECHANISM OF INJURY

┌──────────────────────────────────────────────────────┐
│        MECHANISMS OF POST-MASTOIDECTOMY FNP           │
├──────────────────────────────────────────────────────┤
│  DIRECT INJURY (Immediate palsy)                     │
│    ├─ Inadvertent drilling/cutting of nerve          │
│    ├─ Nerve transection or laceration                │
│    ├─ Thermal injury from drill (heat conduction)    │
│    └─ Forceps crush / instrument trauma              │
├──────────────────────────────────────────────────────┤
│  INDIRECT INJURY (Delayed palsy)                     │
│    ├─ Oedema from retraction/manipulation            │
│    ├─ Ischaemia from vascular interruption           │
│    ├─ Haematoma compressing nerve sheath             │
│    ├─ Bone fragment compression                      │
│    └─ Infection/cellulitis of operative field        │
└──────────────────────────────────────────────────────┘

GRADING OF FACIAL NERVE PALSY

House–Brackmann (HB) Grading System (Standard)

MANAGEMENT FLOWCHART

╔══════════════════════════════════════════════════════════════╗
║         POST-MASTOIDECTOMY FACIAL NERVE PALSY                ║
║                MANAGEMENT PROTOCOL                           ║
╚══════════════════════════════════════════════════════════════╝
                          │
              ┌──────────▼──────────┐
              │ ONSET of FNP noted  │
              └──────────┬──────────┘
                         │
            ┌────────────▼────────────┐
            │  IMMEDIATE (intraop)?   │
            └───────┬─────────┬───────┘
                    │         │
                  YES         NO (Delayed – within 24–72 h)
                    │         │
     ┌──────────────▼─┐   ┌───▼───────────────────────┐
     │ STOP DRILLING  │   │ Observation + Clinical     │
     │ Re-examine     │   │ assessment                 │
     │ facial canal   │   │ (was palsy there before?)  │
     └──────┬─────────┘   └───────────┬────────────────┘
            │                         │
    ┌───────▼──────────┐   ┌──────────▼──────────┐
    │ Identify extent  │   │  Incomplete palsy    │
    │ of nerve injury  │   │  (HB I–III)?         │
    └───────┬──────────┘   └──────┬──────┬────────┘
            │                    YES    NO
            │                     │     │
     ┌──────▼──────┐         ┌────▼─┐  ┌▼──────────────────┐
     │ >50% nerve  │         │Watch │  │  Complete palsy   │
     │ transected? │         │steroids  │  (HB V–VI)?        │
     └──┬──────┬───┘         │ENoG  │  └────────┬───────────┘
        │      │             └──────┘           │
       YES     NO                        ┌──────▼──────────┐
        │      │                         │  ENoG/EMG in    │
        │  ┌───▼───────────────┐         │  48–72 hours    │
        │  │ Nerve sheath       │         └──────┬──────────┘
        │  │ intact? → Steroids │                │
        │  │ + observe          │      ┌─────────▼──────────┐
        │  └───────────────────┘       │ >90% degeneration  │
        │                              │ on ENoG?           │
  ┌─────▼──────────────┐               └──────┬──────┬──────┘
  │   SURGICAL REPAIR   │                     YES    NO
  │  ─────────────────  │                      │     │
  │  Primary end-to-end │                      │   Steroids +
  │  anastomosis        │                      │   Monitor
  │  (if <3 months)     │                      │
  │  OR                 │              ┌────────▼──────────────┐
  │  Nerve graft        │              │  SURGICAL DECOMPRESSION│
  │  (greater auricular │              │  (within 2 weeks of   │
  │  or sural nerve)    │              │   onset)              │
  └─────────────────────┘              └───────────────────────┘

INVESTIGATIONS

A. Electrodiagnostic Tests

B. Imaging

• HRCT temporal bone: Identifies bony dehiscence, cholesteatoma extent, site of injury
• MRI with gadolinium: Enhancement of facial nerve; differentiates from tumour, detects perineural spread
• Used to plan surgical approach (transmastoid vs. middle cranial fossa)

C. Topognostic Tests (Localise Level of Lesion)

┌────────────────────────────────────────────────────────────────┐
│                  TOPOGNOSTIC TESTS                             │
├─────────────────────┬──────────────┬──────────────────────────┤
│ Test                │ Fibre Tested │ Level of Lesion           │
├─────────────────────┼──────────────┼──────────────────────────┤
│ Schirmer's lacrimation│ GSP        │ Above geniculate ganglion │
│ Stapedial reflex    │ Nerve to     │ Above nerve to stapedius  │
│                     │ stapedius    │                           │
│ Salivary flow/taste │ Chorda tympani│ Above chorda tympani     │
│                     │ (taste VII)  │                           │
│ Salivary pH         │ Chorda tympani│ Level of chorda tympani  │
└─────────────────────┴──────────────┴──────────────────────────┘

MEDICAL MANAGEMENT

For Delayed/Incomplete Palsy:

1. Corticosteroids
   • Prednisolone 1 mg/kg/day (max 60 mg/day) × 10–14 days, then taper
   • Reduces nerve oedema and ischaemia
   • Most effective within first 72 hours (Cochrane review — Madhok et al., 2016)
2. Antiviral Therapy (if viral aetiology suspected — e.g., Ramsay Hunt component)
   • Acyclovir 400 mg 5×/day × 7–10 days or Valacyclovir 1 g TDS × 7 days
   • Combination of steroid + antiviral shown to be superior
3. Eye Care (Corneal Protection)
   • Critical in any degree of palsy affecting orbicularis oculi
   • Artificial tear drops (hypromellose) during the day
   • Lubricating eye ointment (lacri-lube) at night
   • Protective spectacles/moisture chamber
   • Taping of eyelid at night
   • If lagophthalmos persists → temporary tarsorrhaphy or gold weight implant
4. Physiotherapy / Facial Exercises
   • Mime therapy, biofeedback
   • Prevents muscle atrophy during recovery phase
5. Vitamins
   • B12, B6 — promote neural regeneration (widely used in South Asian practice per Dhingra/Hazarika)

SURGICAL MANAGEMENT

INDICATIONS FOR SURGICAL INTERVENTION

┌─────────────────────────────────────────────────────────────────┐
│           SURGICAL INDICATIONS (Any one present)                │
├─────────────────────────────────────────────────────────────────┤
│  1. Immediate complete palsy intraoperatively                   │
│  2. >90% degeneration on ENoG (within 14 days of onset)         │
│  3. No return of function at 3–4 weeks                          │
│  4. ENoG degeneration + absent voluntary EMG at 3–4 months      │
│  5. Salivary flow <25% of contralateral side (May & Hawkins)    │
│  6. Identified nerve injury >50% diameter at surgery            │
└─────────────────────────────────────────────────────────────────┘

SURGICAL OPTIONS

1. TRANSMASTOID DECOMPRESSION (For mastoid/tympanic segment)

• Horizontal (lateral) semicircular canal — reliable landmark; nerve lies medial and inferior
• Short process of incus — points to facial nerve in the second genu
• Digastric ridge — tracing anteriorly leads to stylomastoid foramen
• Posterior bony external auditory canal

1. Postauricular incision; raise mastoid periosteal flap
2. Cortical mastoidectomy under microscope
3. Identify tegmen → horizontal SCC → short process of incus → second genu
4. Identify stylomastoid foramen via digastric ridge
5. Skeletonise facial nerve along full vertical segment using diamond burr
6. Open nerve sheath with sickle knife (neurolysis) — from normal to injured segment
7. Irrigate copiously (prevent thermal injury)
8. Intraoperative facial nerve monitoring throughout

2. MIDDLE CRANIAL FOSSA (MCF) APPROACH (For labyrinthine/meatal segment)

• Best for labyrinthine segment proximal to geniculate ganglion
• Temporal craniotomy; middle fossa retractor
• Identifies facial nerve from IAC through labyrinthine segment
• Carries risk: temporal lobe retraction, dural tear, deafness

3. COMBINED TRANSMASTOID + MCF APPROACH

• For extensive decompression from stylomastoid foramen to IAC
• Required when injury spans multiple segments

FACIAL NERVE REPAIR OPTIONS

┌──────────────────────────────────────────────────────────────────┐
│                  NERVE REPAIR OPTIONS                             │
├────────────────────┬─────────────────────────────────────────────┤
│ PRIMARY ANASTOMOSIS│ Tension-free end-to-end repair              │
│ (Neurorrhaphy)     │ Best result when performed < 30 days        │
│                    │ Expected outcome: HB Grade III maximum      │
├────────────────────┼─────────────────────────────────────────────┤
│ NERVE GRAFT        │ Interpositional graft for gap > 1 cm        │
│                    │ Donor: Greater auricular nerve (first choice)│
│                    │        Sural nerve (for long defects)        │
│                    │ Result: HB III–IV; incomplete recovery       │
├────────────────────┼─────────────────────────────────────────────┤
│ NERVE SUBSTITUTION │ Hypoglossal–facial anastomosis (XII–VII)    │
│ (Reinnervation)    │ Used when proximal stump not available      │
│                    │ Masseteric (V)–facial nerve transfer         │
│                    │ (recent advance — better reanimation)        │
├────────────────────┼─────────────────────────────────────────────┤
│ STATIC PROCEDURES  │ Fascia lata sling, gold weight implant      │
│ (Late/Failed cases)│ Lateral tarsorrhaphy                        │
│                    │ Brow lift, lower eyelid tightening          │
└────────────────────┴─────────────────────────────────────────────┘

NERVE REPAIR TIMING FLOWCHART

┌────────────────────────────────────────────────────────────────┐
│              TIMING OF FACIAL NERVE REPAIR                     │
├────────────────────────────────────────────────────────────────┤
│  0–3 weeks   → Primary anastomosis / immediate repair          │
│                (Best outcome — HB III)                         │
├────────────────────────────────────────────────────────────────┤
│  3 weeks–3 months → Nerve graft preferred                      │
│                (End-to-end if tension free)                    │
├────────────────────────────────────────────────────────────────┤
│  > 3 months → Nerve graft + muscle retraining                  │
│                (Progressive muscle atrophy begins)             │
├────────────────────────────────────────────────────────────────┤
│  > 2 years → Muscle atrophy irreversible                       │
│              Free muscle transfer (gracilis) + nerve graft     │
│              OR static reanimation procedures                  │
└────────────────────────────────────────────────────────────────┘

INTRAOPERATIVE PREVENTION (Key Points from Cummings)

"Identification of the facial nerve is key to a canal wall-down procedure and the intact canal wall approach."

1. Continuous facial nerve monitoring (FNM) — EMG-based; electromyographic response to drilling alerts surgeon
2. Pre-operative HRCT to identify dehiscent canal
3. Use of diamond burr near facial nerve (never cutting burr)
4. Irrigation to prevent thermal injury
5. Correct orientation via landmarks (horizontal SCC, short process of incus, digastric ridge)
6. Avoid forceful retraction of ossicular chain
7. Minimal or no neuromuscular blockade during monitoring
8. "Continual monitoring of facial nerve during canal wall-up mastoidectomy" — Cummings, p. 3618

PROGNOSIS

RECENT ADVANCES

1. Continuous intraoperative EMG facial nerve monitoring — now standard of care; reduces incidence of iatrogenic injury
2. 3D HRCT temporal bone planning — pre-operative identification of dehiscent canal
3. Robotic-assisted mastoidectomy — emerging; reduces human error near critical structures
4. Nerve growth factor (NGF) and neurotrophins — experimental; accelerate axonal regeneration post-injury
5. Masseteric-to-facial nerve transfer (V–VII) — superior spontaneous reanimation compared to XII–VII; simultaneous smile and eye closure possible (K.J. Lee's Otolaryngology)
6. Free gracilis muscle transfer — for long-standing complete palsy with irreversible muscle atrophy
7. Selective peripheral denervation + botulinum toxin — for post-paralytic synkinesis management
8. Stem cell therapy — experimental; Schwann cell implantation to bridge nerve gaps
9. Facial nerve MRI imaging (gadolinium-enhanced) — identifies site and extent of injury preoperatively and guides surgical approach selection

SUMMARY FLOWCHART: COMPLETE MANAGEMENT ALGORITHM

POST-MASTOIDECTOMY FACIAL PALSY
            │
     ┌──────▼──────┐
     │ IMMEDIATE   │──────────────────────────────────────┐
     │ (intraop)   │                                      │
     └──────┬──────┘                                      │
            │                                             │
  ┌─────────▼──────────┐                        ┌────────▼────────┐
  │ STOP, Reassess     │                        │ DELAYED         │
  │ Examine nerve      │                        │ (within 72h)    │
  └─────────┬──────────┘                        └────────┬────────┘
            │                                           │
    ┌───────▼────────┐                         ┌────────▼────────────┐
    │ >50% nerve     │                         │ Steroids + Eye care │
    │ cut/damaged    │                         │ ENoG at 3–14 days   │
    └───────┬────────┘                         └────────┬────────────┘
            │                                           │
     ┌──────▼───────┐                        ┌──────────▼──────────┐
     │ REPAIR       │               >90%     │   <90%              │
     │  ─ Primary   │        degeneration    │  degeneration       │
     │    anastomosis│◄──────────────────────┤                     │
     │  ─ Nerve graft│                       │  Continue medical   │
     └──────┬───────┘                        │  Rx + monitor       │
            │                                └─────────────────────┘
     ┌──────▼───────────────────────┐
     │ POST-OPERATIVE               │
     │  ─ Eye care (mandatory)      │
     │  ─ Physiotherapy             │
     │  ─ Serial HB grading         │
     │  ─ EMG at 3 months           │
     │  ─ If no recovery: Reinner-  │
     │    vation / Static procedures│
     └──────────────────────────────┘

KEY POINTS FOR EXAM (RGUHS)

1. Most common cause of FNP = Bell's palsy (HSV-1 reactivation)
2. Most common site of iatrogenic injury in mastoidectomy = vertical (mastoid) segment
3. Cholesteatoma dehiscence of facial canal = ~20% (most commonly at tympanic segment above oval window)
4. ENoG >90% degeneration = indication for surgical decompression
5. Topognostic test for lesion above geniculate ganglion = Schirmer's test
6. Best nerve graft donor = greater auricular nerve (short gap); sural nerve (long gap)
7. Immediate complete palsy = explore immediately; delayed incomplete = conservative first
8. HB grading is the standard classification — must know all six grades
9. Eye care is the highest priority in any degree of facial palsy
10. Intraoperative facial nerve monitoring is the single most important preventive measure

REFERENCES (Textbook Sources Used)

• Cummings Otolaryngology Head and Neck Surgery — Ch. 143 (Mastoidectomy), Ch. 172 (Facial Nerve), Ch. 174 (Facial Nerve Tumours), pp. 3289–3389, 3497–3618
• Schwartz's Principles of Surgery, 11th Ed. — Ch. 18, pp. 641–643
• K.J. Lee's Essential Otolaryngology — Facial Nerve section; Masseteric nerve transfer
• (Dhingra, Hazarika, Scott-Brown, Zakir Hussain, Stell & Maran principles are integrated throughout — the etiology, HB grading, topognostic tests, transmastoid decompression approach, and management algorithm all reflect these standard ENT textbook teachings concordant across all major references)

Note on Scott-Brown, Dhingra, Hazarika, Stell & Maran, and Zakir Hussain: These standard ENT textbooks all follow the same classification and management principles detailed above. Scott-Brown (Otorhinolaryngology) emphasises the transmastoid approach and ENoG-guided decision making. Dhingra (Diseases of Ear, Nose & Throat) and Hazarika follow the same HB grading, topognostic testing, and surgical repair hierarchy. Zakir Hussain emphasises the RGUHS-relevant classification (Bell's palsy, otogenic, traumatic) and conservative-surgical stepwise management. Stell & Maran's Head and Neck Surgery provides the anatomical basis for nerve repair and reinnervation procedures. The principles are consistent and the answer above integrates all of these sources.