it is a mixed nerve having both motor and sensory roots motor root supplies the muscles of facial...
TRANSCRIPT
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