Anatomy of the Facial Nerve: 

• 3 segments: intracranial, infratemporal and extratemporal (in general we get tested most commonly on the extratemporal branches and anatomy of the facial nerve) 
• Infratemporal region contains the narrowest portion of the fallopian canal (called meatal foramen)- temporal fractures can cause facial paralysis
• The initial infratemporal branches control parasympathetic function to the lacrimal gland and the parotid gland
• The next three nerves branch at the level of the mastoid : (1) nerve to the stapedius muscle, (2) the sensory auricular branch, and the (3)  chorda tympani which supplies taste sensation to the anterior 2/3 of the tongue and provides parasympathetic innervation to the submandibular and submental regions 
• Extratemporal: the extratemporal branches start as the nerve exits the stylomastoid foramen passing anterior to the posterior belly of the digastric and lateral to the styloid process of the temporal nerve 
• Divides into Superior and inferior divisions at the posterior edge of the parotid gland
• Superior division: branches into the temporal, zygomatic, and buccal
• Inferior division: branches into the marginal mandibular and cervical 

Important Anatomic Landmarks (and other fun testable tidbits) for the Extratemporal Facial Nerve:

• Temporal branch:
• Pitanguy’s line –> 0.5cm below the tragus to 1.5cm above the lateral brow
• Lies within temporopareital fascia
• Does not arborize (more likely for permanent injury)

• Marginal mandibular nerve: 
• Lies superficial to the facial artery and vein (water UNDER the bridge)
• Nerve is located above the inferior border of the mandible in 81% of people
• Does not arborize (more likely for permanent injury) 

• The zygomatic and buccal branches arborize significantly therefore there is not significant benefit to fixing nerve injuries to branches of the zygomatic or buccal medial the lateral canthus 

• All muscles receive innervation from facial nerve from their deep surface EXCEPT MLB (Mentalis, levator anguli oris, buccinator) which receive innervation from the superficial surface 

• Exam:
• Frontalis: raise eyebrows
• Orbicularis: close eyelids
• Zygomatic branch: smile
• Orbicularis: purse lips

Etiology of facial paralysis: (we are focusing mainly on extratemporal causes of facial paralysis) 

• Iatrogenic: Bells Palsy – this is the most common cause of facial palsy 
• Diagnosis of exclusion 
• Resolves completely in 70-85% of patients. If paralysis does not completely resolve, the most common remaining problem is with ectropion or inability to completely close the eye 
• Steroids can be used within 24 hours of diagnosis
• Trauma: 
• Second most common cause of facial paraplysis 
• Most commonly by transverse temporal bone fractures followed by penetrating wounds
• Repair – plan to repair before 72 hours because the neurotransmitters are still functional so the nerve can be stimulated for identification of the distal target 
• After repair wait 6 months before any further investigation because nerves take a long time to regenerate 
• Tumors: 
• Presentation: think neoplasm if… unilateral facial weakness slowly increasing for more than 3 months
• Common tumors: cholesteatoma, primary parotid, acoustic neuroma, metastases
• Infections: 
• Viral: Varicella, herpes, EBV
• Ramsay Hunt Syndrome: varicella-zoster virus infection with facial paralysis, ear pain, rash in external auditory canal
• Treat with steroids
• Lyme disease
• Can cause bilateral facial palsy
• Treat Lyme with doxycycline
• Congenital:
• Mobius Syndrome:
• Definition: congenitally underdeveloped cranial nerve 6 (abduscens) and cranial nerve 7 (facial) leading to unilateral or bilateral loss of eye abduction and facial paralysis 

• CULLP: congenital unilateral lower lip palsy
• Normal resting tone but have marginal mandibular dysfunction with activation. Is most commonly noticed when the baby is crying
• Associated with other major congenital anomalies in 3/4 of children
• **In a pediatric patient with unilateral facial weakness, obtain CT scan to evaluate temporal bone

Testing for Facial Paralysis: 

• Exam: 
• Evaluate eyes 
• lids:  ectropion, corneal exposure, lagophthalmos
• Tear production 
• Visual acuity 
• Evaluate nasal obstruction – from paralysis of the nasalis muscle
• Evaluate oral competence and speech – from paralysis of the orbicularis oris 

• House-brackmann Facial nerve grading system

• Diagnostic Studies: 
• CT scan – good for evaluating for tumors and bony details. In kids with unilateral facial paralysis plan for CT scan to evaluate temporal bone abnormalities 
• MRI – good for evaluating the nerve 
• Nerve studies: 
• EnoG and EMG 

Treatment Considerations:

• Goals: 
• Restoration of symmetry at rest 
• Restoration of dynamic expression 
• Corneal protection 
• Restoration of oral competence 
• Considerations: 
• Time from injury: 
• Notably at 18-24 months and definitely by 3 years the facial muscles have undergone denervation atrophy and are therefore not able to be used for further reconstruction. 
• Status of the nerve and completeness of the paralysis 

Operative Techniques:

• Direct Repair: 
• Requires short time frame from injury to repair – most often within 72 hours of a sharp injury 

• Interposition Nerve Graft 
• This allows for direct repair when a nerve gap exists precluding direct, tension free repair 
• Expect that the nerve will regenerate at 1 -1.5mm/day and can be monitored by an advancing Tinel’s sign 

• Cross Facial Nerve Graft: 
• This is indicated when (1) the proximal ipsilateral facial nerve stump is unavailable for grafting (2) a distal stump is present (3) the muscles are still capable of function after reinnervation 
• Sural nerve graft is most often used to connect fascicles of the corresponding peripheral nerve branches from the non-paralyzed side to the paralyzed side. Because you are taking innervation signals from the contralateral nerve this allows for better symmetric facial movement.  
• Babysitter procedure – this is used if the denervation time has been > 6 months. 40% of the ipsilateral hypoglossal nerve is transferred to the facial nerve stump to prevent atrophy and loss of motor endplates while axonal growth occurs through the cross facial nerve graft 

• Nerve Transfers: 
• This is indications when (1) the proximal ipsilateral facial nerve stump is unavailable for grafting (2) a distal stump is present (3) the muscles are still capable of function after reinnervation (4) the contralateral facial nerve is unavailable for use – think bilateral facial paralysis such as with Mobius syndrome 
• For these cases the masseter nerve is most commonly used. The hypoglossal can also be used but is not favored because it causes tongue atrophy and using the hypoglossal bilaterally would lead to tongue paralysis 

• Regional Muscle Transfers: 
• This is indicated when (1) muscles are unable to be used due to long term atrophy 
• Temporalis Muscle Transfer: 
• Most commonly used for animation of the eyelids, ala, or oral commissure
• Used more commonly than the masseter because it has a greater excursion and adaptability to the orbit 
• Masseter Muscle Transfer: 
• Most commonly used for motion around the mouth 

• Free Functional Muscle Transfer: 
• This is indicated when (1) muscles are unable to be used due to long term atrophy
• Advantages to microvascular transfer vs regional muscle transfers: increased ability for spontaneous and symmetric expression because the contralateral facial nerve is being used as the innervation (facial nerve vs trigeminal nerve)
• Free functional muscle transfer options:
• Gracillis: most commonly used due to reliable vascular pedicle, one direction of pull, no overlying tendon, single nerve (does not reach contralateral side)
• Others: pec minor, serratus, latissimus. 
• Stages: 
• 2 stage: cross facial nerve transfer followed by free muscular transfer
• 1 stage: ipsilateral nerve to masseter

• Static: 
• Brow 
• Brow lift vs weaken contralateral side with botulinum toxin
• Eye 
• Treatment of lagophthalmos: 
• Gold weight in upper lid: placement superficial to levator aponeurosis and tarsal plate with the inferior portion of the plate 2-3mm from lash line, between the medial and central thirds of the lid to bring the upper lid within 2-4mm of the lower lid to allow for coverage of the cornea. 

• Treatment of Ectropion: 
• Canthopexy for paralytic ectropion or FTSG for cicatricial ectropion
• Mid-Face: suture suspension (SOOF lift)
• Nose: 
• Nasalis and levator labii superioris responsible for dilating the nasal apertures (buccal branch of facial nerve). Can treat occlusion/stenosis with slings, rhinoplasty, suture suspension 
• Oral Commissure: Fascial strips for static suspension sling of soft tissues 

Complications

• Synkenesis: unintentional motion in one area of the face produced during intentional movement in another area of the face often due to aberrant regeneration of the nerve. Can be treated with retraining or botox 
• Hyperkinesis: hyperactivity of contralateral normal side.  may be treated with Botox or mirror feedback