It is a mixed nerve having both motor and sensory roots motor root supplies the muscles of facial expression

Sensory root has afferent fibres conveying taste sensation from anterior 2/3rds of tongue and efferent which are parasympathetic and secretomotor

FACIAL NERVE

The course of the nerve divided into

1. Intra cranial

2. Intratempora

3. Extratemporal

Intracranial :

Motor nucleus situated in the floor of the fourth ventricle where it winds round the 6th nerve nucleus producing facial colliculus

Taste sensation is conveyed to the tractus solitarious secretomotor fibres arise from the superior salivary nucleus

Upper part of the motor nucleus which innervates fore head muscles receives fibres from both sides of cerebral hemispheres

Lower part of the nucleus which supplies lower face gets only crossed fibres from one hemisphere

SENSORY NUCLEUS

The function of fore head muscles is preserved in supra nuclear lesions because of bilateral innervation

Facial nucleus also receives fibres from thalamus by alternate routesand provides involuntary controlto facial muscles

The emotional movements as smiling and crying are thus preserved in supranuclear lesions

The two roots of the facial nerve emerge from the lower border of the pons and enter the internal auditory meatus along the 8th nerve

Intratemporal part :

1. Meatal segment : within internal acoustic meatus

2. labyrinthine segment : Two roots fuse together at the fundus of the I .A .M and pass laterally over the labyrinth

Then the nerve reach the medial wall of the middle ear just behind the processus cochleariformis

The nerve forms the anterior genu here and is wider known as Geniculate ganglion

In labyrinthine segment the canal is narrow and is prone to early compression in bells palsy

Tympanic segment :

From the geniculate ganglion it passes just above the oval windowand below the lateral semicircular canal

Mastoid segment :

From the pyramid to stylomastoid foramen

Extra cranial part :

From the stylomastoid foramento its peripheral branches

Branches of facial nerve :

Greater superficial petrosal nerve

It arises from the geniculate ganglion carries secretomotor fibres to lacrimal gland and nasal mucosa

Nerve to stepedius :

It arises at the level of second genu supplies stepedius muscle

Cordatympani:it arises from the middle of the vertical segment passes between malleus and incus leaves the tympanic cavity through petrotympanic fissure

It carries secretomotar fibres to submandibular and sublingual glands

Taste from the anteroir 2/3rdsof the tongue

Communicating branch : It joins the auricular branch of vagus

It supplies the concha ,retroauricular groove, posterior meatus and outer surface of the tympanic membrane

Posterior auricular nerve :

It supplies muscles of pinna occipital belly of occipitofrontalis

Communicates with auricular branch of vagus

Muscular branches to :

Stylohyoid

Posterior belly of diagastric

Occipital belly of occipitofrontalis

Poterior auricular muscles

Terminal branches to muscles of facial expression

Temporal .Zygomatic .Buccal mandibular. Cirvical

SURGICAL LAND MARKS OF FACIAL NERVE

Processus cochleariformis

Oval window and horizontal secircular canal

Short process of incus

Pyramid

Tympanomastoid suture

Diagastric ridge

SEVERITY OF THE NERVE INJURY

Neuropraxia :

Physiological block with no anatomical disruption

It lasts only few days full return of function is expected

Aaxonotomesis :

Axon sheath is intact but the axon is devided.

Degeneration of the nerve fibres occur sheath remains intact, most of the fibres tend to regenerate, mismatching may occur leading to synkinesis

Neuronotmesis :

Whole nerve is severed degeneration of the distal segment occur neuroma may form at the lesion from excessive fibrosis and scaring the end result of this condition is poor

Based on anatomical structure of the nerve :

Class 1 :

Only axon itself is effected as in a physiological block

Class 2 :

Division in the individual axon but not in the surrounding perineurium

Class 3 :

The axon and perineurium are devided but not endoneurium

Class 4 :

The axon and perineurium and endoneurium are all divided but not the nerve sheath itself

Class 5 :

It is synonymous with neuronotmesis

CAUSES OF FACIAL PARALYSIS

The commonest cause of facial palsy

This is a lower motor neuron lesion of unknown cause

Both sexes are equally effected

Positive family history is present in 6-8% of patients

Risk of bells palsy is more in diabetics (angiopathy) and pregnant women (retention of fluid )

BELL’S PALSY

Viral infection :

Herpes simplex ,herpes zoster or E. B virus

Other cranial nerves may also be involved in bells palsy which is thus considered a part of the total picture of polyneuropathy

AETIOLOGY

Vascular ischaemia :

It may be primary or secondary

Primary ischeamia induced by cold or emotional stress

Secondary ischeamia is the result of primary which causes increased cappillary permiability leading to exudation of fluid, oedema and compression of microcirculation of the nerve

Hereditary :

The fallopian canal is narrow because of hereditary predisposition and this makes the nerve susceptible to early compression with slightest oedema 10% have the positive family history

Autoimmune disorder :

T-lymphocyte changes have been observed

Clinical features :

On set is sudden patient unable to close the eye

On attempting to close the eye the eye ball turns up and out (bells phenomenon)

Due to the loss of blinking epiphora is present

Deviation of angle mouth to opposite side

Drooping of the corner of the mouth

Loss of taste

Pain arround the ear may be present

T.M normal

Hearing tests normal

Typical bells palsy has certain characters :

It is acute onset unilateral

Numbness or pain present in face neck or tongue in majority of cases

Loss or decreased ipsilateral stapedial reflex in majority of cases

Red or congested chorda tympani present

Lesions at c.p angle :

Associated with paralysis of other nerves like 8th, 5th, 6th nerves

Lesions at internal auditory canal :

Associated with 8th nerve paralysis

Slow and complete loss of facial nerve function occurs

SITES OF LESIONS

Lesions at geniculate ganglion :

Dry eye, dry mouth diminished taste sensation.

Greater superficial petrosal nerve is involved

Tympanomastiod segment lesions :

Loss of stapedial reflexand chorda tympani nerve function

Lesion at the parotid gland :

Individual branches are involved

No hearing defect

Salivary flow

Taste are normal

In bells palsy exact site of lesionnot known

Now a days it is thought that petrous part lateral to the internal auditory canal is the narrowest part and is the common site of lesion

Some people feel it is due to viral infection in the brain stem

Histopathology :

Hypereamia of nerve sheath oedema of the nerve

Wallerian degeneration with vascular engorgement

Topographic tests :

Shirmer’s tests :

Lacrimation is absent if greater superficial petrosal nerve is involved

Tests for taste sensation electrogustometry for testing taste sensatoin over the tongue

FACIAL NERVE FUNCTION TESTS

Normal response is metallic taste, shock is felt if paralysed

Lesions of chordatympani causes altered taste sensation

Salivary flow tests :

By cannulating whartons duct

Stapedial reflex lost due to involvement of nerve to stapedius

Electrodiagnostic tests :

Minimal N. E.T :

Nerve isstimulated at steadily increasing intensity till facial twich is just noticeable

This is compared with normal sideno difference bet normal and paralysed side in conduction block

Nerve excitability is lost in injuries where degeneration sets in when the difference bet two sides exceeds 3.5mm the test is positive for degeneration. it takes 48 to72hrs after injury

M.S.T :

Maximum facial movement is determined and compared with normal side

Electroneurography :

It gives information about the proportion of fibres in the nerve that have degenerated

Surgical decompression is indicated when summation potential falls to 10% of the normal value

Electromyography :

It records spontaneous activity of facial muscles by direct insertion of electrodes into the muscles denervated muscle shows fibrillation potentials but they appear only 14 to 21 days after denervation has started

It is useful to show earliest signs of recovery

General :

Reassurance care of the eye to prevent exposure keratitis

Relief of pain by analgesics

physiotherapy to facial muscles

TREATMENT

Medical management :

Steroids : Prednisalone1mgper kgbody wt bd

for 5days If the pt is recovering, dose is tapered

during the next 5 days If the paralysis remains complete the

same dose is continued for another10days, tapered in next 5days

Steroids also useful to prevent synkinesis,crocodile tears and to shorten the recovery time of facial paralysis

Steroids can be combined with acyclovir

Vasodilaters vitamines mast cell inhibitors antihistamines are also useful

Surgical treatment :

Nerve decompression relieves pressures on the nerve and improves microcirculation of the nerveprognosis is good in incompletepalsy and in those where clinical recovery starts within 3 weeks of onset

MELKERSSON’S SYNDROME

Consists of triad of facial paralysis

Swelling of lips and fissured tongue paralysis may be recurrent

Rx is same as in bells palsy

Recurrent facial palsy seen in bells palsy

Melkerssons syndrome diabetes sarcodosis and tumours recurrent palsy on the same side may be caused by tumour in30%of cases

Incomplete recovery :

Eye cannot be closed resulting inepiphora

Weak oral sphincter causesdrooling of saliva and difficulty in taking food

COMPLICATIONS OF FACIAL PALSY

Exposure keratitis : Tear film from the cornea evaporates

causing dryness, exposure keratitis corneal ulcer it can be prevented by artificial tears (methylcellulose drops)every 1 – 2 hrs

Eye ointment proper coverfor the eye at night

Ttemporary tarsoraphy may also be indicated

Synkinesis :

When the patient wishes to close the eye corner of the mouth also twichesIt is due to cross innervation of fibresno treatement for this condition

Tics and spasms :

Result of regeneration of fibres, invountary movements seen on the effected side

Contractures :

They result from fibrosis of atrophied muscles they effect

Movement of the face

But facial symmetry at rest is good

Crocodile tears (gustatory lacrimation ) :

Unilateral lacrimation with mastication

This due to faulty regeneration of parasympathetic fibres which now

Supply lacrimal gland instead of salivary glands

It can be treated by section of greater superficial petrosal nerve or tympanic neurenectomy

Freys syndrome :

There is sweating and flushing of skin over the parotid during mastigation

It result from parotid surgery

Surgery of facial nerve :

Decompression :

The bony canal is exposed and uncapped the sheath of the nerve is also slit to relieve pressure due to oedema or intraneural heamatoma

End to end anastomosis :

If the gap is few mm in extratemporal part there should not be any tention in theapproximated ends

Nerve graft :

Great auricular,lateral cutaneous nerve of thigh or sural nerve

Hypoglossal-facial anastomosis :

Plastic procedures :

Facial slings, face lift operations

Slings of masseter and temporalis muscles