Facial paralysis causes significant functional and aesthetic defects that often lead to great psychosocial distress. The goal of management in patients with facial paralysis of any etiology is to maximize functional recovery and minimize cosmetic deformity. When complete paralysis is due to either anatomic discontinuity or irreversible neural degeneration, the facial nerve requires repair or decompression for the most optimal functional and aesthetic results. 


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OUTLINE


Facial Nerve Decompression Surgical Approaches

INTRODUCTION

Decompression : opening the bony canal and nerve sheath to release pressure and reduce compression on nerve fibers.
The goal of decompression is to improve blood circulation and minimize damage to distal nerve fibers.
The facial nerve is the longest nerve that travels in a bony canal with a complex course and high susceptibility to injury
lack of expansion room in a rigid bony canal, potentially leading to severe nerve damage and even necrosis and fibrosis


INTRODUCTION
Facial paralysis causes significant functional and aesthetic defects that often lead to great psychosocial distress
The goal of management in patients with facial paralysis of any etiology is to maximize functional recovery and minimize cosmetic deformity
 When complete paralysis is due to either anatomic discontinuity or irreversible neural degeneration, the facial nerve requires repair or decompression for the most optimal functional and aesthetic results
Anatomy 
Motor root: 7000 axons
Sensory root (Nervus intermedius / Wrisberg): 3000 axons
Motor: facial muscles
Secretomotor: lacrimal, submandibular, sublingual
Taste: anterior 2/3rd of tongue
Sensory: Post-aural / concha / ext. auditory canal

Anatomy
Segments of Facial Nerve
1. Intra-cranial (12 mm): Brain stem to entry into IAC
2. Meatal (10 mm): Within Internal Auditory Canal
3. Labyrinthine (4 mm): Fundus of I.A.C. to Geniculate gangl.
4. Tympanic (11 mm): Geniculate ganglion to pyramid
5. Mastoid (13 mm): Pyramid to stylomastoid foramen
6. Extra-temporal (15 mm): S.M. foramen to pes anserinus

Anatomy

Anatomy
Surgical landmarks
Cochleariform process: lies 1 mm inferior to geniculate ganglion at anterior end of tympanic segment. 
Cog: bony ridge hanging from tegmen tympani lies 1 mm above & posterior to cochleariform process.
Incus short process: 2 mm below lies external genu 
Lateral Semicircular Canal: 2 mm Antero-Infero-Medial lies external genu
Oval window: 1 mm above lies external genu

Surgical landmarks
Tympano-mastoid suture in posterior canal wall: 5-8 mm medial lies mastoid segment of facial nerve
Digastric ridge in mastoid tip: leads antero-medially to mastoid segment of facial nerve 
Groove between mastoid  & bony E.A.C. meatus: bisected by facial nerve
Tragal pointer: 1 cm antero-infero-medial is facial nv
Root of styloid process: lateral lies facial nerve
Superior border of posterior belly of digastric: superior & parallel lies facial nerve

Etiology of Facial Nerve Palsy
1. Idiopathic (55%): Bell’s palsy,                                               
2. Temporal bone trauma (25%): Road traffic accident
3. Infection (10%): C.S.O.M., Herpes Zoster oticus 
                              Malignant otitis externa,cholesteatoma
4. Neoplasm (5%): Parotid tumors, Acoustic Neuroma, 
                               Glomus tumors, Malignancy of ear
5. Congenital (4%): Moebius syndrome ,Melkersson Rosenthal syndrome
6. Iatrogenic :         Mastoidectomy, Parotid surgery
7. Metabolic (rare): Diabetes mellitus, Hypertension

Nerve injury 
structure of nerve 


HOUSE-BRACKMANN FACIAL NERVE GRADING SYSTEM 

Topo-diagnostic tests
Audiometry: cochlear nerve function  
Vestibulometry: vestibular function
Schirmer’s test: Greater Superficial Petrosal Nerve 
Stapedial reflex test: Nerve to stapedius
Electrogustometry: Chorda tympani
Submandibular salivary flow: Chorda tympani
Examination for terminal facial nerve branches



Electrical testing 
Primary diagnostic modality for surgical decision making 
Estimate the severity of nerve injury ,Prognosis 
Most reliable and objective  tests are ENoG and EMG  
Of value only with complete facial paralysis  

Electro-neuronography
Measures the amount of intact axons relative to the healthy side 
Useful between 4 and 21 days of onset of complete paralysis
Degeneration > 90% correlated with poor prognosis


Electromyography
Needle electrodes placed within the facial musculature measures spontaneous and voluntary electrical activity in the facial muscle
Assessing the muscle denervation and reenervation
adjunct to ENoG if surgical decompression is being considered
polyphasic action potentials indicate muscle reinnervation
fibrillation potentials detected 2 to 3 weeks after injury indicate significant muscle denervation and poor recover


Facial nerve decompression

Performed in severe cases when the facial nerve is seriously deteriorating 
Patient are at high risk of permanent paralysis and have a poor prognosis without aggressive intervention
To be effective surgery must be performed within 2 weeks of the onset of symptoms 

Preoperative planning 
ENOG :10% or less muscle function on affected side compared with normal side from 3-14 days post complete paralysis
EMG : absence of motor unit action potential
HRCT : trauma ,otitis media.
MRI  : suspicion of underlying tumor 
Audiometric tests : associated hearing loss , surgical approach ,

Site to be explored
Based on causes of facial paralysis and suspected site of injury 
Bells palsy : the labyrinthine segment and perigeniculate region are decompressed via a middle fossa approach.
Acute or chronic otitis media : the mastoid and tympanic segments are explored
Canal wall down mastoidectomy :cholesteatoma involving facial nerve
Intraoperative injury :directed to the site of injury 
Surgical approaches 


Selection of the surgical approach is determined by the location of the facial nerve injury and hearing status in the affected ear
Trans-mastoid approach 
Middle cranial fossa approach 
Translabyrinthine  approach

Transmastoid approach 
Indication 
Tumors limited to mastoid and tympanic segment 
Longitudinal fracture limited to mastoid segment 
AOM,COM involving tympanic segment and mastoid segment 
Limitations
Limited access to geniculate ganglion
No access to labyrinthine segment 


Trans-mastoid approach 






The junction of the facial nerve and geniculate ganglion is reached with further anterior and medial dissection under the head of the malleus


Once the fallopian canal in the tympanic and mastoid segments has been exposed, any residual impinging bony spicule is removed. 
The nerve sheath is opened at the site of injury and for a short distance proximal and distal to the site of injury to assess the severity of injury to the fascicles.
 If the fascicles are intact, the decompression procedure is complete.
 If more than 50% of the nerve fascicles have been violated or the nerve is completely transected, primary neurorrhaphy or cable grafting is indicated.

 The postauricular wound  is closed in layers 
Mastoid dressing is applied to the operated ear for 24 hours.

Complications 
 Further surgical trauma to the facial nerve
Hearing loss (either conductive or sensorineural), 
Vertigo
CSF leak
Wound infection.

Middle Fossa Approach

Exposure from IAC to  tympanic segment (for intracanalicuar and labyrinthine segments)
Indication:
Bells palsy
Longitudinal temporal bone fractures 
Advantages 
A)No hearing impairment ,even geniculate ganglion and tympanic segment can be decompressed 
b)Combined with retrolabyrinthine ,transmastoid for enttire facial nerve exposure 

 6x8cm trap door incision above ear ( 
 4x4 cm temporalis fascia graft harvested 
 Anterinferior based temporalis musculo perisosteal flap elevated 

 A bone flap centered over zygoma elevated, taking care middle meningeal artery on inner table

 Dura elevated from posterior to anterior till petrous ridge, arcuate eminence, meatal plane, and GSPN Anteriorly.


 Blue lining of superior semicircular canal seen 
Anterior to it IAC opened with 7th nerve anterosuperiorly (BILLS BAR FORMS LATERAL BOUNDARY OF MEATAL FORAMEN) 
 Labrynthine segment followed laterally till geniculate ganglion. 
 Tegmen tympani removed 
 Tympanic segment blue lined and final layer of bone removed with elevator and decompressed 












 Epitympanic defect covered with temporalis fascia. 
The roof of the IAC is sealed with a small abdominal fat graft.
The skin flap is then reapproximated in two layers without the use of any drain
 A mastoid dressing is placed over the operated ear for 3 days postoperatively

Complications 
 Sensorineural hearing loss
Vertigo
Edema of the temporal lobe 
Subdural hematoma
CSF leak 
Meningitis.
brainstem and cerebellar infarction 
 Injury to AICA
Translabyrinthine approach

The translabyrinthine approach can be utilized for decompression of the entire intratemporal course of the facial nerve in cases where cochleovestibular function is already lost
Indication 
Transverse temporal bone fracture, 
 Extensive facial neuroma, or a 
Large congenital cholesteatoma that extends into the IAC.
Advantages 
Entire nerve is exposed using a single approach 



incision is made 3 cm behind the postauricular crease and carried inferiorly over the mastoid tip.
A portion of the occipital bone posterior to the sigmoid sinus also should be exposed.
An extended complete mastoidectomy is performed.
The bone over the sigmoid sinus is removed, along with 0.5 to 1.0 cm of bone posterior to this structure.

The facial recess is opened
Inferior to the posterior semicircular canal, bone is removed, exposing the jugular bulb, posterior fossa dura, and endolymph
Bone is removed 180 degrees around the internal canal
The dura over the IAC and cerebellar plate can be opened to expose the cerebellopontine cistern and brainstem
Closure is accomplished with a 4- × 4-cm piece of temporalis fascia covering the dural defect and draped over the aditus to separate the mastoid from the middle ear 
Abdominal fat is harvested and used to obliterate the mastoid space.