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Facial Nerve


Fig: Forehead receives bilateral innervation and is thus saved in supranuclear paralysis. Emotional movements controlled by thalamo nuclear fibres are also preserved.
  1. Course:  
    1. Intracranial part: Pons to the internal auditory meatus (I.A.M)
    2. Intratemporal part: Internal auditory meatus (IAM) to stylomastoid foramen
      1. Meatal Part: i. (8-10 mm)  ii. Part present the internal to auditory meatus    
      2. Labyrinthine segment:    i. (3-5 mm)
        1. From the fundus of the I.A.M to the      geniculate ganglion
        2. Ist genu}: the nerve Takes its turn    
      3. Tympanic (Horizontal) segment:  i. (10-12 mm)
        1. From geniculate ganglion to oval window
      4. Vertical segment (Mastoid) :        
        1. (9-16 mm)
        2. From oval window to Stylomastoid foramen
        3. 2nd the tympanic and the vertical segment
    3. Extracranial course: Stylomastoid foramen to its peripheral branches.
Fig: A Course of facial nerve. Intratemporal part consists of four segments: Meatal
1. abyrinthine 2. Tympanic 3. Mastoid 4. B. Branches of Facial nerve on face.
  1. Branches of the facial nerve:
    1. Greater Superficial Petrosal nerve
      1. Lacrimal glands             
      2. Nasal glands
      3. Palatine glands              
      4. Pharyngeal glands
    2. Nerve to stapedius (2nd genu)
    3. Chorda tympani (from middle of the vertical segment)
    4. Communicating branch : To Arnold’s nerve (auricular branch of Vagus) (Concha, retroauricular   groove and canal wall postero-superior)      
    5. Posterior auricular nerve (auricular and occipital belly of occipitofrontalis)
    6. Never to posterior belly of digastric
    7. Nerve to stylohyoid
    8. Peripheral branches (pes anserinus) - temporal, zygomatic, buccal, mandibular, cervical
  2. Landmarks:
    1. 1 - Geniculate ganglion;
    2. Processus cochleariformis
    3. (geniculate ganglion lies above and medial to it)
    4. Oval window
    5. Short process of incus
    6. Digastric ridge
    7. Lateral Semicircular canal
  3. Chorda Tympani:
    1. Is the terminal branch of nerves intermedius
    2. Arises 4 mm from the stylomastoid foramen
    3. Enters the tympanic cavity through the posterior canaliculus and exists through the petrotympanic fissure (Gasserian fissure)
    4. Carries taste fibres from the anterior 2/3 of the tongue and also supplies secreomotor fibres to
    5. submandibular and sublingual glands
  4. Electrodiagnostic Test:
    1. Nerve Excitability testing (NET):Minimal Nerve Excitability Test
      1. Electrical stimulus is varied from 2.4 -16.2 mA
      2. Nerve is stimulated at the stylomastoid foramen- facial twitch is observed
      3. Lowest current required to produce the twitch is compared to the opposite side
        Result: significant; if difference > 3.5 m amp, degenerative changes detected > 48-72 hrs
    2. Maximal stimulation test (MST): Stimulus producing maximum twitch is recorded
    3. Electro neuronography: (EnoG)  
      1. Muscle’s compound action potential is recorded and not that of the nerve
      2. Most useful test form the 3rd to 14th day of the onset of palsy
      3. Stimulation of the facial nerve is performed at the stylomastoid foramen and muscle response recorded in the nasolabial area
      4. Is the best guideline for facial nerve decompression; indicated when value <10% of NIs a good prognostic indicator
    4. Electromyography (E.M.G)
      1. Records the spontaneous activity of the facial muscles
      2. Is not useful in acute facial palsy
      3. Since it takes 14-21 days for fibrillation potential to develop
      4. Is the most reliable test to follow the course of denervation
      5. Alerts the physician to subclinical evidence of early regeneration/recovery.
  5. Topodiagnostic Tests:
    Are tests designed to localized the site of lesion
    1. Tear test: (Schirmer’s test)
      1. Whatman’s filters paper; 35*5 mm is used
      2. The paper is placed between the outer 1/3 and the middle l/3rd of the lower lid
      3. Wetting of the filter paper is observed after 5 mins
      4. (N) wetting = 10-25 mm
    2. Stapedial reflex (tested by Tympanometry)
    3. Taste:
      1. Performed using an electrogustometer
      2. Electric taste thresholds are checked on both sides
      3. Difference of > 20 mamp is significant
    4. Salivary flow test (submandibular glands)
      1. No. 50 polyethylene tube is introduced into the Wharton’s duct of B/L sides
      2. The number of drops produced in 1" and 5' are calculated
      3. Decreased in 25% is significant
  1. Causes of Facial  Paralysis
  1. Central
    1. Brain abscess                 
    2. Pontine gliomas            
    3. Poliomyelitis                  
    4. Multiple sclerosis         
  2. Intracranial part (cerebellopontine angle)
    1. Acoustic neuroma                        
    2. Meningioma                  
    3. Congenital cholesteatoma
    4. Metastatic carcinoma                  
    5. Meningitis
  3. Intra temporal part
    1. Idiopathic
      1. Bell’s palsy
      2. Melkersson’s syndrome
    2. Infections
      1. Acute suppurative otitis media                             
      2. Chronic suppurative otitis media
      3. Herpes zoster oticus                                               
      4. Malignant otitis externa
    3. Trauma
      1. Surgical: Mastoidectomy                                        
      2. Stapedectomy
      3. Accidental: Fractures of temporal bone         
    4. Neoplasms
  1. Malignancies of external and middle ear
  2. Glomus jugulare tumour
  3. Facial nerve neuroma
  4. Metastasis to temporal bone (from cancer of breast, bronchus, prostate)


Extra Edge. Battle’s sign ecchymosis over the mastoid seen in fractures of temporal bone.



Extra Edge: Frey’s syndrome. There is flushing and sweating of skin of parotid region during eating. It is seen after parotidectomy. Parasympathetic fibres supplying the parotid gland are misdirected after parotidectomy and innervate sweat glands of the parotid area. Tympanic (Jacobson’s) neurectomy will interrupt these fibres.

  1. Extracranial part
    1. Malignancy of parotid
    2. Surgery of parotid
    3. Accidental injury in parotid region                                                                           
    4. Neonatal facial injury (obstetrical forceps)           
  2. Systemic diseases
    1. Diabetes mellitus
    2. Hypothyroidism                            
    3. Uraemia
    4. Polyarteritis nodosa
    5. Wegener’s granulomatosis
    6. Sarcoidosis (Heerfordt’s syndrome)
    7. Leprosy
    8. Leukaemia
    9. Demyelinating disease
  1. Complications Following Facial Paralysis
    Peripheral facial paralysis due to any cause may result in any of the following complications:
    1. Incomplete recovery.
    2. Exposure keratitis.
    3. Synkinesis (mass movement).
    4. Tics and spasms.
    5. Contractures.
    6. Crocodile tears (gustatory lacrimation). There is unilateral lacrimation with mastication. This is dueto faulty regeneration of parasympathetic fibres which now supply lacrimal gland instead of the salivary glands. It can be treated by section of greater superficial petrosal nerve or tympanic neurectomy.
    7. Frey’s syndrome (gustatory sweating). There is sweating and flushing of skin over the parotid during mastication. It results from parotid surgery.
    8. Psychological and social problems. Drooling dur­ing eating and drinking and impairment of speech cause social problems.
  1. Hyperkinetic Disorders Of Facial Nerve
    They are characterised by involuntary twitching of facial muscles on one or both sides.
    1. Hemifacial spasm. It is characterised by repeated, uncontrollable twitching of facial muscles on one side. It is of two types
      1. Idiopathic
      2. Secondary:  acoustic neuroma, congenital cholesteatoma or glomus tumour.
        Idiopathic type has been treated by selec­tive section of the branches of facial nerve in the parotid or by puncturing the facial nerve with a needle in its tympanic segment.
        Botulinum toxin has been used in the affected muscle. It blocks the neuromuscular junction by preventing release of acetylcholine.
    2. Blepharospasm. Twitching and spasms are lim­ited to orbicularis oculi muscles on both sides. The eyes are closed due to muscle spasms causing functional blind­ness.
      1. The cause is uncertain, but probably lies in the basal ganglia.
      2. It is treated by selective section of nerves supply­ing muscles around the eye on both sides.
      3. Botulinum-A toxin injected into the periorbital mus­cles gives relief for 3-6 months.
Surgery Of Facial Nerve
  1. Decompression.                                   
  2. End to end anastomosis.
  3. Nerve graft (cable graft).                     
  4. Hypoglossal facial anastomosis.
  5. Plastic procedures. 

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