Facial nerve• The facial nerve is 7/12 paired cranial nerves.• emerges from the brainstem between the pons and the medulla, and controls the muscles of facial expression, and functions in the conveyance of taste sensations from the anterior two-thirds of the tongue and oral cavity.• also supplies preganglionic parasympathetic fibers to several head and neck ganglia.• The motor part of the facial nerve arises from the facial nerve nucleus in the pons while the sensory part of the facial nerve arises from the nervus intermedius.
Anatomy of Facial Nerve Branches• The facial nerve exits the posterior cranial fossa (PCF) at the internal acoustic meatus.• Within the internal acoustic meatus the facial nerve enters the facial canal.• 1 branch of the facial nerve, the greater superficial petrosal nerve (GSPN) branches from the geniculate ganglion within the genu of the facial canal and enters the middle cranial fossa by way of the hiatus of the canal for the GSPN.• 2 branch of the facial nerve, the stapedial nerve, branches from the descending portion of the facial nerve and enters the middle ear.• 3 branch of the facial nerve, the chorda tympani nerve, branches from the descending portion of the facial nerve and enters the middle ear. Within the middle ear the chorda tympani nerve crosses the medial surface of the tympanic membrane. It then passes through the petrotympanic fissure to enter the infratemporal fossa.• The descending portion of the facial nerve continues into the parotid region by way of the stylomastoid foramen.
• The motor & sensory part of the facial nerve enters the petrous temporal bone via the internal auditory meatus (intimately close to the inner ear)• emerges from the stylomastoid foramen and passes through the parotid gland, where it divides into five major branches. Though it passes through the parotid gland• The facial nerve forms the geniculate ganglion prior to entering the facial canal.
Inside skullGreater petrosal nerve - provides parasympathetic innervation to lacrimalgland, sphenoid sinus, frontal sinus, maxillary sinus, ethmoid sinus, nasal cavity, aswell as special sensory taste fibers to the palate via the Vidian nerve.Nerve to stapedius - provides motor innervation for stapedius muscle in middle earChorda tympani Submandibular gland Sublingual gland Special sensory taste fibers for the anterior 2/3 of the tongue.
Outside skullDistal to stylomastoid foramen, the following nerves branch offthe facial nerve:• Posterior auricular nerve - controls movements of some ofthe scalp muscles around the ear• Branch to Posterior belly of Digastric and Stylohyoid muscle• Five major facial branches (in parotid gland) - from top tobottom: • Temporal auricular and fronto-occipitalis muscles • Zygomatic muscles of the zygomatic arch and orbit • Buccal muscles in the cheek and above the mouth • Marginal mandibular muscles in the region of the mandible • Cervical the platysma muscle
functionEfferent• Its main function is motor control of most of the muscles of facial expression. It also innervates the posterior belly of the digastric muscle, the stylohyoid muscle, and the stapedius muscle of the middle ear.• The facial also supplies parasympathetic fibers to the submandibular gland and sublingual glands via chorda tympani. Parasympathetic innervation serves to increase the flow of saliva from these glands. It also supplies parasympathetic innervation to the nasal mucosa and the lacrimal gland via the pterygopalatine ganglion.• The facial nerve also functions as the efferent limb of the corneal reflex.
• Afferent• In addition, it receives taste sensations from the anterior two-thirds of the tongue via the chorda tympani, taste sensation is sent to the gustatory portion of the solitary nucleus. General sensation from the anterior two-thirds of tongue are supplied by afferent fibers of the third division of the fifth cranial nerve (V-3). These sensory (V-3) and taste (VII) fibers travel together as the lingual nerve briefly before the chorda tympani leaves the lingual Nerve to enter the tympanic cavity (middle ear) via the petrotympanic fissure. It thus joins the rest of the facial nerve via canaliculus for chorda tympani. Facial nerve then meets the geniculate ganglion (sensory ganglion of taste fibers of chorda tympani and other taste pathways). From geniculate ganglion the taste fibers continue as the intermediate nerve which goes to the upper anterior quadrant of fundus of internal acoustic meatus along with the motor root of facial nerve. intermediate nerve reaches the posterior cranial fossa via the internal acoustic meatus before synapsing in the solitary nucleus. The cell bodies of the Chorda tympani reside in the geniculate ganglion, and these parasympathetic fibers synapse at the submandibular ganglion, attached to the lingual nerve.• The facial nerve also supplies a small amount of afferent innervation to the oropharynx below the palatine tonsil. There is also a small amount of cutaneous sensation carried by the nervus intermedius from the skin in and around the auricle (earlobe).
Aetiology• In a LMN lesion the pt cant wrinkle their forehead (unless a lesion in the parotid spares the temporal branch) - the final common pathway to the muscles is destroyed. Lesion in pons, or outside brainstem (post. fossa, bony canal, middle ear or outside skull).• In an UMN lesion, the upper facial muscles are partially spared because of alternative pathways in the brainstem (unless bilateral lesion). Different pathways for voluntary and emotional movement. CVAs usually weaken voluntary movement often sparing involuntary movements (e.g. spontaneous smiling). The much rarer selective loss of emotional movement is called mimic paralysis and is usually due to a frontal or thalamic lesion.
Investigation• Serology - Lyme, herpes and zoster (paired samples 4-6 weeks apart).• Check BP in children with Bells palsy (2 case reports of aortic coarctation).• Schirmer tear test (reveals reduced flow of tears from an affected greater palatine nerve).• Stapedial reflex (an audiological test absent if stapedius muscle is affected).• Electrodiagnostic studies (generally a research tool) reveal no changes in involved facial muscles for the first three days, but a steady decline of electrical activity often occurs over the next week, and will identify the 15% with axonal degeneration.
Branch of CN VII Location of Lesion Actions Posterior auricular Posterior auricular Pulls ear backward Occipitofrontalis, Moves scalp backward occipital belly Temporal Anterior auricular Pulls ear forward Superior auricular Raises ear Occipitofrontalis, Moves scalp forward occipital belly Corrugator supercilii Pulls eyebrow medially and downward Procerus Pulls medial eyebrow downward Temporal and Orbicularis oculi Closes eyelids and zygomatic contracts skin around eyeZygomatic and buccal Zygomaticus major Elevates corners of mouth
Buccal Zygomaticus minor Elevates upper lip Levator labii Elevates upper lip and midportion superioris nasolabial fold Levator labii Elevates medial nasolabial fold and nasal superioris alaeque ala nasi Risorius Aids smile with lateral pull Buccinator Pulls corner of mouth backward and compresses cheek Levator anguli oris Pulls angles of mouth upward and toward midline Orbicularis Closes and compresses lips Nasalis, dilator Flares nostrils naris Nasalis, Compresses nostrils compressor naris
Buccal and Depressor anguli Pulls corner ofmarginal oris mouth downwardmandibular Depressor labii Pulls lower lip inferioris downwardMarginal Mentalis Pulls skin of chinmandibular upwardCervical Platysma Pulls down corners of mouth
Case Report• 59/malay/female• c/o: unable to tolerate orally well due to ulcer at rt lateral tongue• k/c: facial nerve palsy grade IV, on permanent tracheostomy (last tube changed 4/10/12 on double lumen 8.0)• PMH: petroclival meningioma (rt)• PSH: post craniotomy and debulking of tumor at HUSM on 4/6/2009• PDH: NKMI• Allegies: -
Findings• G/C: alert, wheelchair, can’t talk• E/O: – Assymetrical face (rt face paralysed) – On tracheostomy – Rt eyelid can’t closed + blind• I/O – Mouth opening good – OH bad – Retain root 16,15,14,13,25,44,43, – Traumatic ulcer 2x2cm at rt lt tongue
BELL’S PALSY• One of the common disorder affecting facial nerve causing one sided paralysed face• Caused: unknown, vascular, infection, genetic, immunologic origin, brain lesion• Sign: common c/o weakness on one side face with drooling eyelid or coner of the mouth, othr c/o dry eyes,altered sound, increased sensitivity to sound
House-Brackman Scale (facial nerve palsy) • Grade I Normal symmetrical function • Grade II Slight weakness noticeable only on close inspection Complete eye closure with minimal effort Slight asymmetry of smile with maximal effort Synkinesis barely noticeable, contracture, or spasm absent • Grade III Obvious weakness, but not disfiguring May not be able to lift eyebrow Complete eye closure and strong but asymmetrical mouth movement Obvious, but not disfiguring synkinesis, mass movement or spasm
House-Brackman Scale (facial nerve palsy) • Grade IV Obvious disfiguring weakness Inability to lift brow Incomplete eye closure and asymmetry of mouth with maximal effort Severe synkinesis, mass movement, spasm • Grade V Motion barely perceptible Incomplete eye closure, slight movement corner mouth Synkinesis, contracture, and spasm usually absent • Grade VI No movement, loss of tone, no synkinesis, contracture, or spasmHouse JW, Brackmann DE. Facial nerve grading system. Otolaryngol. Head Neck Surg 1985; 93:146–147.
Management• Pharmagological : – Corticosteroid: prednisolone (1mg/kg/day - adult 60- 80 mg/day – can divide dose bd) PO 7-10d within 72h is of proven benefit – Antiviral agents: valacyclovir (1g PO q8h)• Surgical: Surgical transmastoid decompression of the facial nerve in severe cases is being investigated. Cosmetic surgery or anastomosis of hypoglossal nerve to the facial nerve may help if nerve fails to regenerate• Artificial tears/lubricants & eyeglasses to proted eye• Physical therapy (fasial exercise), acupunture with or without electrical stimulation
Gently raiseSit relaxed in Draw your Wrinkle up your eyebrows, you canfront of a eyebrows nose. help the movementmirror. together, frown. with your fingers. Hold pencil or Turn down bottom Blow out cheeks. Curl up top lip. lollipop stick between lips.
Reference• Lo,Bruce (2010). Bell’sPalsy: http://emedicine.medscape.com/article/791311-overview• Jean Hatchell, Cambridge University Hospitals NHS Foundation Trust, Hills Road, Cambridge, CB2 0QQ www.cuh.org.uk, Exercises_for_facial_weakness• House JW, Brackmann DE. Facial nerve grading system. Otolaryngol. Head Neck Surg 1985; 93: 146–147.