Facial nerve Apooorv Pandey.

Content Introduction Anatomy Clinical Examination Applied aspect

Facial nerve

Seventh CN- mixed nerve. Nerve of second brachial

arch Nerve of facial expression.

The facial nerve (CN VII) – motor + sensory

Parasympathetic secretory fibers submandibular, sublingual salivary glands lacrimal gland mucous membranes of Oral and nasal

cavities.

Sensory functions: Taste sensation (eardrum and external auditory

canal) sensation: the muscles it supplies

Infranuclear

Nuclear

Four components

Supranuclear

Pyramidal and extrapyramida

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ANATOMY

SUPRANUCLEAR ANATOMY

Has specific areas on the cerebral cortex.

Facial pyramidal fibers begin

It is represented according to the part it supplies on the face.

Path of voluntary facial expressions (Pyramidal)

Contralateral precentral gyrus are carried through corticobulbar tract (pyramidal)

Internal Capsule

Midbrain

Cross over to the opposite side

Motor Facial nerve nucleus in Pons.

DeJong's The Neurologic Examination, 6th Edition

Facial Nerve has 4 nuclei (lower pons)

1. Motor nucleus

2. Sup salivolacrimatory nucleus (parasympathetic)

3. Nucleus of tractus solitarius (gustatory)

4. Spinal tract nucleus (sensory)

Nuclear / Intra-axial Anatomy

DeJong's The Neurologic Examination, 6th Edition

Motor nucleus fibres

Ventrolateral pontine tegmentum

Floor of fourth ventricle forming

facial colliculus Fibers then course anterolaterally to exit lateral

brainstem at pontomedullary junction

Sup salivolacrimatory nucleus (parasympathetic)Nucleus of tractus solitarius (gustatory)Spinal tract nucleus (sensory)

NERVOUS INTERMEDIUS

DeJong's The Neurologic Examination, 6th Edition

The facial nerve leaves the brainstem in two roots

MOTOR ROOT (70%)

NERVOUS INTERMEDIUS (30%)

Extra-axial course

Emerge from lateral brainstem at root exit zone on pontomedullary junction just caudal to the roots of CN V

Cerebellopontine angle (CPA) cistern

DeJong's The Neurologic Examination, 6th Edition

Cisternal segment

Has 2 roots at the exit Larger motor root anteriorly Smaller sensory nervus intermedius posteriorly

CN8 exits brainstem posterior to CNVII

These nerves resemble the nerve roots of the spinal cord in that

they are devoid of epineurium but covered in piamater and

bathed in cerebrospinal fluid.Diagnostic and imaging anatomyHarnsberger

Intrapetrous course of the facial nerve has two portions:

(a) in the internal auditory canal (b) in the facial canal or Fallopean

aqueduct

The internal auditory segment is 7 to 8 mm in length

At the entrance to the internal auditory canal (IAC)

The facial nerve at this point lies in

close proximity to the anterior inferior cerebellar artery

(AICA)

In its course through the facial canal the nerve has four segments:

1) Labyrinthine II) Horizontal or tympanicIII) PyramidalIV) Mastoid

Bell’s Palsy: Diagnosis and Management JEFFREY D. TIEMSTRA, MD, and NANDINI KHATKHATE, MD University of Illinois at Chicago College of Medicine, Chicago, Illinois

The labyrinthine segment lies laterally between the cochlea and vestibule,toward the medial wall of the tympanic cavity

It extends from the internal auditory canal to the geniculate ganglion. (3–5 mm)

The nerve turns abruptly and runs horizontally for about 1 cm (horizontal or tympanic segment)

Turns backward and arches downward behind the tympanic cavity.

Extends from the geniculate ganglion to the second turn of the facial nerve

External genu & geniculate ganglion

The tympanic nerve segment is covered by a thin bony sheath.

The pyramidal segment joins the horizontal and mastoid segments, and gives off the branch to the stapedius muscle.

The mastoid segment (13–15 mm)

extends from this point to the

stylomastoid foramen.

In the adult, it is protected laterally by the mastoid tip, tympanic ring and mandibular ramus.

Whereas in children younger than 2 years it is relatively superficial.

Postauricular incisions in this younger population must be carefully planned because the trunk of the facial nerve is a subcutaneous structure at this level.

Pesanserinus

SensoryGreater sup. petrosal

nerveChorda tympani

MotorNerve to stapediusPosterior auricularNerve to DiagastricNerve to stylohyoidMuscles of facial

expression

Branches

After exiting the stylomastoid foramen, the facial nerve gives off branches to

The posterior auricular The posterior belly of digastric The stylohyoid

Post auricular branch Ascends btw EAM and mastoid Divides into auricular and occipital

branches

Digastric branch Posterior belly of digastric

Stylohyoid branch Stylohyoid muscle

Final Innervation

Innervates the muscles of facial expression.

General Somatic Efferents

Parasympathetic fibres

Temporal bone

via the petrosal foramen

Enters middle cranial fossa

via the foramen lacerum

And reaches the base of medial pterygoid plate

Meet sympathetic fibers of deep petrosal nerve.

The parasympathetic and sympathetic fibers together make up the nerve of the pterygoid canal

Greater Superficial Petrosal Nerve

Upon exiting the pterygoid canal, pre-ganglionic parasympathetic fibers of CN VII synapse in the pterygopalatine ganglion

(which is suspended from the fibers of the maxillary division of the trigeminal nerve (V2) in the

pterygopalatine fossa.)

Post-ganglionic parasympathetic the lacrimal gland (via the lacrimal

nerve) mucous membranes of the nasal and

oral pharynx

Special Visceral Afferents or Sensations

Corda Tympani Course

The fibers pass through the middle ear in close relationship with the tympanic membrane and exit the base of the skull to enter the inferotemporal fossa.

In the inferotemporal fossa the chorda tympani joins the lingual branch of the mandibular division of CN V (V3).

Pre-ganglionic fibers synapse in the submandibular ganglion

Post-ganglionic fibers then enter the submandibular gland

General Somatic Afferents

Applied aspect

(1829): THE DISCOVERY

OF THE NERVE OF FACIAL EXPRESSION

Sir Charles Bell (1829)

3 cases of facial paralysis due to facial nerve trauma.

Causes of nerve palsy

Clinical Examination of the facial nerve

Motor

Frontalis, Corrugator Supercilii Orbicularis oculi Buccinator Orbicularis Oris Platysma

Sensory

Evaluation of taste on the anterior two-thirds of the tongue.

Four fundamental tastes (sweet, sour, salty and bitter)

and asymmetries documented.

Reflex and Parasympathetic Function

Corneal Reflex Lacrimation

Salivation

Other important tests

1. Schirmer's Tear test

2. Nerve conduction and Potential

Studies

3. CT / MRI

Inflammatory facial nerve lesions can be demonstrated by MRI after gadolinium contrast administration.

Otogenic and traumatic facial paralysis should always be evaluated by thin-slice bone-window CT scanning of the temporal bone.

Testing facial nerve function

90% of nerve disorder occurs along the nerves intra temporal course

Electro diagnosis – testing degree of distal axonal degeneration

Topognosis – testing function of accessory branches

Facial nerve tests:

Topognosis - lacrimation, stapedial reflex, salivary flow, taste

CT- to rule out trauma to the nerve

Prognosis – Electromyography (EMG) Electrical Nuro Graphy (ENoG)

Diagnostic – Blink reflex, EMG, ENoG

Electro diagnostic testing

EMG-electromyography Is a electro physiologic test It measures electrical response

1. During needle insertion2. At rest

3. During volitional movement

Nerve conduction time:

Nerve stimulated near the foramen and record one of the facial muscle group

Latency for each action potential is defined as the time between onset of stimulus and onset of response

Cortical innervation of left

face

Upper half: BiLateral

Lower Half: Predominantly contralateral

Left

Lower Motor Neuron (LMN) Lesion

Clinical Examination

Upper Motor Neuron (UMN) Palsy

Facial ParalysisUPPER MOTOR NEURON LOWER MOTOR NEURON

Lesions is above the pons. Lesions is in the pons or in the pathway from pons to its exit.

Patient can make furrows on looking upwards

Furrows are absent on looking upwards of the affected side of face.

Lower part of the face is involved on the opposite side of the lesion.

The whole face and forehead involved on the same side of the lesion.

Isolated involment of this type is rare.

Isolated involment of this type is common.

It is invariably associated with hemiplegia .

It may be associated with hemiplegia .

GRADING

 Dr John W. House and Dr Derald E. Brackmann, otolaryngologists in Los Angeles,

who first described the system in 1985.

Vrabec JT, Backous DD, Djalilian HR, et al. (April 2009). "Facial Nerve Grading System 2.0". Otolaryngol Head Neck Surg 

Localization of Lesions Affecting Cranial Nerve VII

Supranuclear Lesions (Central Facial Palsy)

Nuclear and Fascicular Lesions (Pontine Lesions)

Peripheral Facial Nerve Palsy

Nuclear Lesions May affect either the nucleus of the facial nerve or its

intrapontine axons

Ipsilateral Facial palsy with

Abducens fascicle or nucleus

Paramedian Pontine Reticular Formation

(PPRF)

(paralysis of conjugate gaze to the psilateral side)

Corticospinal tract (contralateral hemiplegia)

Abducens fascicle or nucleus

PERIPHERAL LESIONS

Lower motor lesion of Facial nerve

• Palsy +loss of taste sensation – in the

canal

• Palsy +loss of taste +hyperacusis – just

after entrance into the canal

• All the above + loss of hearing – at the

internal auditory meatus

• All the above + lateral rectus damage –

cerebo potine angle involvement Bell’s

palsy.

Millard-Gubler Syndrome

Lesion located in the ventral pons that destroys the fascicles of the facial and

abducens nerves and the corticospinal tract

Ipsilateral peripheral-type facial paralysis

Ipsilateral lateral rectus paralysis

(diplopia with failure to abduct

the ipsilateral eye)

Contralateral hemiplegia

Foville Syndrome

Lesion located in the pontine tegmentum that destroys the fascicle of the facial nerve, the PPRF, and the corticospinal tract.

Ipsilateral peripheral-type facial paralysis

Paralysis of conjugate gaze to the side of the lesion

Contralateral hemiplegia

Möbius syndrome

Möbius syndrome results from the underdevelopment of the VI and VII cranial nerves.

Loss of facial expressions and horizontal gaze.

EXTRAPYRAMIDAL SYSTEM

Consist of basal ganglia and the descending motor projections other than the fibers of the pyramid or cortico-bulbar tracts.

Extrapyramidal system, involves diffuse axonal connections between multiple regions including the basal ganglia, hypothalamus, and motor cortex.

The extrapyramidal system is capable of producing involuntary facial movements (absence of major pyramidal pathways)

A dissociation between voluntary facial movements (volitional facial palsy) and emotional facial movements (emotional or mimetic facial palsy)

Important points during Embryonic Development

• 7th cranial nerve is first identifiable at the end of 3rd week

• Important steps in facial nerve development occurs throughout gestation and the nerve is not fully developed until appx 4yrs after birth.

• Because the cell collection also gives rise to the 8th cranial (acoustic) nerve, it is referred to as the facioacoustic cranial primordium or crest.

During its development the facial and Vestibulochochlear nerve are not distinguishable till the 37th day of the embryonic life.

The facial nerve is the nerve of the second branchial arch and its branch, chorda tympanic develops as the nerve to the first branchial arch during the early embryonic period.

6th an 7th cranial nerve motor nuclei lie in close approximation

Congenital Mobius syndrome Acquired inflammatory /vascular / neoplastic

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