FACIAL NERVE PALSY

COMPONENTS OF FACIAL NERVE

Brancial motor (special visceral efferent)	Supplies the muscles of facial expression; posterior belly of digastric muscle; stylohyoid, and stapedius
Visceral motor (general visceral efferent)	Parasympathetic innervation of the lcrimal, submandibular, and sublingual glands, as well as mucous membranes of nasopharynx, hard and soft palate.
Special sensory (special afferent)	Taste sensation from the anterior 2/3 of tongue; hard and soft palates.
General sensory (general somatic afferent)	General sensation from the skin of the concha of the auricle and from a small area behind the ear.

 Functional Component Overview of Facial Nerve

Pathway of Cranial Nerve VII (Facial Nerve)

Origin and Central Course of Brachial Component of Facial Nerve

The branchial motor component originates from the motor nucleus of CN VII in the caudal pons. Fibers leaving the motor nucleus of CN VII initially travel medially and dorsally to loop around the ipsilateral abducens nucleus (CN VI) producing a slight bulge in the floor of the fourth ventricle - the facial colliculus.

Fibers then course so as to exit the ventrolateral aspect of the brainstem at the caudal border of the pons in conjunction with the nervus intermedius components of CN VII.

Intracranial course

Upon emerging from the ventrolateral aspect of the caudal border of the pons, all of the components of CN VII enter the internal auditory meatus along with the fibers of CN VIII (vestibulocochlear nerve). The fibers of CN VII pass through the facial canal in the petrous portion of the temporal bone. The course of the fibers is along the roof of the vestibule of the inner ear, just posterior to the cochlea.

At the geniculate ganglion the various components of the facial nerve take different.

Figure: Showing branches of facial nerve proximal to geniculate ganglion

Fibers of the branchial motor component pass through the geniculate ganglion without synapsing, turn 90 degrees posteriorly and laterally before curving inferiorly just medial to the middle ear to exit the skull through the stylomastoid foramen. The nerve to the stapedius muscle is given off from the facial nerve in its course through the petrous portion of the temporal bone.

Extracranial Course and Final Innervation

The posterior auricular nerve, nerve to the posterior belly of the digastric and the nerve to the stylohyoid muscle are given off upon the facial nerve's exit from the stylomastoid foramen. The remaining fibers enter the substance of the parotid gland and divide to form the temporal, zygomatic, buccal, mandibular, and cervical branches to innervate the muscles of facial expression.

Voluntary Control of the Muscles of Facial Expression

Signals for voluntary movement of the facial muscles originate in the motor cortex (in association with other cortical areas) and pass via the corticobulbar tract in the posterior limb of the internal capsule to the motor nuclei of CN VII.

Fibers pass to both the ipsilateral and contralateral motor nuclei of CN VII in the caudal pons .The portion of the nucleus that innervates the muscles of the forehead receives corticobulbar fibers from both the contralateral and ipsilateral motor cortex. The portion of the nucleus that innervates the lower muscles of facial expression receives corticobulbar fibers from only the contralateral motor cortex. This is very important clinically as central (upper motor neuron) and peripheral (lower motor neuron) lesions will present differently.

Facial Nerve Palsy

Etiology and Diagnosis

v     Many conditions can produce isolated facial nerve palsy identical to Bell's palsy

v     Patients with Bell's palsy usually progress from onset of symptoms to maximal weakness within three days and almost always within one week

v     Classically, Bell's palsy has been defined as idiopathic

v      infection with herpes simplex virus type 1 (HSV-1) is a possible cause because research has found elevated HSV-1 titers in affected patients

Differential Diagnosis for Facial Nerve Palsy

DISEASE	CAUSE	DISTINGUISHING FACTOR
NUCLEAR(PERIPHERAL)
LYME DISEASE	Spirochete Borrelia burgdorferi	History of tick exposure, rash, or arthralgias; exposure to areas where Lyme disease is endemic
OTITIS MEDIA	Bacterial pathogens	Gradual onset; ear pain, fever, and conductive hearing loss
RAMSY HUNT SDYNDROME	Herpes zoster virus	Pronounced prodrome of pain; vesicular eruption in ear canal or pharynx
SARCOIDOSIS OR GUILLAIN-BARRÉ SYNDROME	Autoimmune response	More often bilateral
TUMOR	Cholesteatoma, parotid gland	Gradual onset
SUPRANUCLEAR(CENTRAL)
MULTIPLE SCLEROSIS	Demyelination	Additional neurologic symptoms
STROKE	Ischemia,hemorrhage	Extremities on unaffected side often involve
TUMOR	Metastases, primary brain	Gradual onset; mental status Changes; history of cancer

Evaluation

Ø      A patient with an acute onset of unilateral facial weakness most likely has Bell's palsy

Ø       gradual onset of more than two weeks' duration is strongly suggestive of a mass lesion

Ø      Medical history should include recent rashes, arthralgias, or fevers; history of peripheral nerve palsy; exposure to influenza vaccine or new medications; and exposure to ticks or areas where Lyme disease is endemic

Ø       physical examination should include careful inspection of the ear canal, tympanic membrane, and oropharynx, evaluation of peripheral nerve function in the extremities and palpation of the parotid gland.

Two types of Lesion and their Differnces

Upper Motor Neuron Lesion (UMN)

Results from damage to neuronal cell bodies in the cortex or their axons that project via the corticobulbar tract through the posterior limb of the internal capsule to the motor nucleus of CN VII. With an UMN lesion, voluntary control of only the lower muscles of facial expression on the side contralateral to the lesion will be lost. Voluntary control of muscles of the forehead will be spared due to the bilateral innervation of the portion of the motor nucleus of CN VII that innervates the upper muscles of facial expression. UMN lesions are usually the result of a stroke.

Lower Motor Neuron (LMN) Lesion

Results from damage to the motor nucleus of CN VII or its axons. A LMN lesion results in the paralysis of all muscles of facial expression (including those of the forehead) ipsilateral to the lesion.

Clinical Correlation - Bell's Palsy

A Lower Motor Neuron lesion of CN VII which occurs at or beyond the stylomastoid foramen is commonly referred to as a Bell's Palsy. Characteristic indications of a LMN lesion or Bell's Palsy include the following, on the affected side:

· Marked facial asymmetry

· Atrophy of facial muscles

· Eyebrow droop

· Smoothing out of forehead and nasolabial folds

· Drooping of the mouth corner

· Uncontrolled tearing

· Loss of efferent limb of conjunctival reflex (cannot close eye)

· Lips cannot be held tightly together or pursed

· Diificulty keeping food in mouth while chewing on the affected side

Ø      A Lower Motor Neuron lesion of CN VII in conjunction with deficits associated with CN VI (abducens nerve) indicates a lesion in the brainstem which affects both the motor nucleus of CN VII and the abducens nucleus.

Ø       A Lower Motor Neuron lesion of CN VII in conjunction with deficits associated with CN VIII (vestibulocochlear nerve) are characteristic of a lesion in the region of the internal acoustic meatus. An example of this type of lesion is an acoustic neuroma.

Figure: Diagram showing Differences in Innervation and Lesions in Upper motor

Neuron and Lower Motor Neuron Lesion

Peripheral Lesions of Facial Nerve

Ø       Paralysis of all the muscles of facial expression ipsilateral to the lesion (LMN lesion of the branchial motor component of CN VII).

Ø      Loss of secretion from lacrimal gland and mucous membranes of nasal and oral pharynx ipsilateral to the lesion (lesion of the greater petrosal nerve, visceral motor component of CN VII).

Ø       Loss of secretion from submandibular and sublingual glands ipsilateral to the lesion (lesion of the chorda tympani, visceral motor component of CN VII).

Ø       Loss of taste from anterior 2/3 of tongue ipsilateral to the lesion (lesion of the chorda tympani, special sensory component of CN VII).

Ø       Loss of general sensation from concha of external ear and small area of skin behind the ear (general sensory component of CN VII).

Ø       Deficits in hearing and/or vestibular functions ipsilateral to the lesion  (associated with CN VIII).

Ø       Intact general sensation to the tongue (supplied by CN V3).

Examination

Ø      Upon noticing facial asymmetry, proceed to tests VII nerve functions

·         Look up (frontalis) and attempt to push the folds down, close your eyes (orbicularis oculi) and attempt to force them open, and frown (corrugator superficialis)

·         Look for exposure keratitis, tarsorraphy

·         Nasolabial fold, show your teeth and and blow against closed lips

·         Look for drooling of saliva

Ø      Determine UMN or LMN, unilateral or bilateral

Ø      UMN unilateral

·         Examine UL and look for hemiparesis on the same side of the facial weakness

·         Check for xanthelesma, DM signs and BP

Ø      LMN unilateral

·         Examine other CN

·         VI nerve and contralateral weakness in brainstem lesions

·         CPA lesion (V, VI, VII and VIII with cerebellar)

·         Other CN nerves involvement non-conforming type

·         Basal meningitis lesions

·         Mononeuritis multiplex, MG

·         Therefore proceed to examine the neck

Ø      Look at the Palate for vesicles

Ø      Examine the parotids and for surgical scars

Ø      Mastoid tenderness

Ø      Examine the neck for cervical LNs

Ø      Upper limbs

·         Contralateral hemiparesis

·         Ipsilateral cerebellar

Ø      Ask to examine

·         Otoscopy for vesicles in EC and otitis media

·         For hyperacusis (sensitive to high-pitched or loud sounds)

·         For loss of taste in the anterior two-thirds of the tongue

·         Urine dipstick for glucose and BP

Ø      Upon noticing facial diplegia, proceed with

Ø      Rule out MG (Bilateral ptosis)

Ø      Rule out Dystrophia myotonica or fascio-scapular-humeral dystrophy

Ø      Bilateral LMN VII

·         Test for frontalis, corrugator and orbicularis oculi

·         Ask patient to show teeth and blow against closed lips

·         Look for V, VI, VIII

·         Examine parotids (Sarcoidosis, amyloidosis)

·         Examine tongue (scrotal tongue for MR syndrome)

·         Examine the upper limbs for GBS, MND, leprosy, Lyme’s (radiculopathy) and bilateral cerebellar signs if suggestive of bilateral CPA tumors

·         Think of rare: Melkersson-Rosenthal syndrome, Mobius syndrome