facial nerve anatomy (2)

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I THINK IT WILL BE HELPED TO MY JUNIOR

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ANATOMY OF FACIAL NERVE: 

ANATOMY OF FACIAL NERVE PRESENTED BY DR RAJESH KUNDU PGT ,ENT,NBMC

Introduction : 

Introduction VII Cr Nerve ; Mixed N 10,000 Motor , Sensory , parasympathetic fibers Motor root – 7000 special visc . eff. Fibers Sensory & Parasymp . – 3000 fibers carried by “ NERVUS INTERMEDIUS ”(N of wrisberg )

Facial nerve: types of fibers: 

Facial nerve: types of fibers Special Visceral Efferent/ Branchial Motor General Visceral Efferent/Parasympathetic General Sensory Afferent/Sensory Special Visceral Afferent/Taste

Special Visceral Efferent/Branchial Motor : 

Special Visceral Efferent/ Branchial Motor Premotor cortex  motor cortex  corticobulbar tract  bilateral facial motor nuclei ( pons )  facial muscles Stapedius , stylohyoid , posterior digastric , buccinator

General Visceral Efferent/Parasympathetic : 

General Visceral Efferent/Parasympathetic Superior salivatory nucleus ( pons )  nervus intermedius  greater/superficial petrosal nerve  facial hiatus/middle cranial fossa  joins deep petrosal nerve ( symp fibers from cervical plexus)  thru pterygoid canal (as vidian nerve)  pterygopalatine fossa  spheno / pterygopalatine ganglion  postganglionic parasympathetic fibers  joins zygomaticotemporal nerve(V2)  lacrimal gland & seromucinous glands of nasal and oral cavity Superior salivatory nucleus  nervus intermedius  chorda  joins lingual nerve  submandibular ganglion – postganglioic parasympathteic fibers  submandibular and sublingual glands

General Sensory Afferent/Sensory : 

General Sensory Afferent/Sensory Sensation to auricular concha , EAC wall, part of TM, postauricular skin Cell bodies in geniculate ganglion

Special Visceral Afferent/Taste: 

Special Visceral Afferent/Taste Postcentral gyrus  nucleus solitarius –> tractus solitarius – nervus intermedius  geniculate ganglion – chorda tympani  joins lingual nerve  anterior 2/3 tongue, soft and hard palate

Structure of nerve : 

Structure of nerve From inside out Nerve fibre consists of axon ,myelin sheath,neurilemma & endoneurium A group of nerve fibre is enclosed in a sheath called perineurium to form a fascile The fascicles are bound together by epineurium

Components of a Nerve : 

Components of a Nerve Endonerium Surrounds each nerve fiber Provides endoneural tube for regeneration Much poorer prognosis if disrupted Perinerium Surrounds a group of nerve fibers Provides tensile strength Protects nerve from infection Pressure regulation Epinerium Surrounds the entire nerve Provides nutrition to nerve

Facial Nerve Nuclei : 

Facial Nerve Nuclei 3 nuclei Motor nucleus – lower pons below 4 th ventricle Superior salivatory nucleus – dorsal to motor N N of tractus solitarius – medulla oblongata

Central Connections of FN: 

Central Connections of FN Upper part of Nucleus – B/L supra nuclear innervation Lower part of Nucleus– C/L inn. Imp – function of forehead preserved in supranuclear lesions

Course : 

Course

DIVISIONS OF FACIAL NERVE: 

DIVISIONS OF FACIAL NERVE

Intra cranial portion : 

Intra cranial portion From brainstem to fundus of IAM length 24mm Facial N crosses CP angle with 8 th CN & NI Devoid of epineurium Thin layer of pia mater Surg imp : Iatrogenic trauma in CP angle tumour surgery Difficult to identify in schwannoma (no connective tissue)

Meatal Segment : 

Meatal Segment Enters in ant sup segment of IAC Length 5 – 12 mm No separate sheath Shares with NI & 8 th CN Bath in CSF

Intra Temporal Region : 

Intra Temporal Region Length – 28 to 30 mm Longest bony canal 3 segments by 2 genus

Labyrinthine Segment : 

Labyrinthine Segment Narrowest(0.68) & Shortest(3-5mm) Meatal foramen No anastomosing arteries Periostium is thicker Posterosuperior to cochlea Anteromedial to SSCC Posterior to vestibule Distal end – Geniculate ganglion;1 st genu Internal auditory canal

PowerPoint Presentation: 

Surgical importance: Anatomical bottle neck – ischemia in oedema Part most vulnerable for ischemia(no arterial anastomosis ) Temporal bone # - MC injured Geniculate ganglion :(distal end) Bipolar ganglion cells Afferent input pain & taste febres Secretomotor fiber to lacrimal gland(without synapse)GSPN

Tympanic Segment : 

Tympanic Segment From Geniculate ganglion to 2 nd genu Length – 8 to 11mm Lies beneath LSCC & above OW At its proximal end,above & medial to “ Processus cochleariformis & TT muscle

Cont..: 

Cont.. Creats 2 recesses Facial recess (lat) Sinus tympani(med)

Cont..: 

Cont.. Surgical importance: Processus cochleariformis ( consistant landmark) Imp landmark for 2 nd genu - Hug the inf. LSCC -Pyramidal eminence -B/w short process of incus (L) & LSCC(M) CT SMF Mastoid

Mastoid Segment : 

Mastoid Segment From 2 nd genu (PM) to SMF(AL) Longest (13mm) Landmark – “ Digastric Ridge” identified by medial aspect of mastoid tip FN leaves FC via SMF(b/w mastoid tip & styloid process) Has 3 brances CT N to stapedius sensory auricular branch

Extra Temporal Region : 

Extra Temporal Region From SMF to terminal branches Runs in substance of parotid Main trunk divides - upper temperofacial - lower cervicofacial “ Pes anserinus ” Superficial to Retromandibular V & Ext.carotid art

Branches of facial N : 

Branches of facial N Intra temporal region : GSPN N to stapedius Chorda tympani Sensory auricular branch

GSPN: 

GSPN From Geniculate ganglion 2 types of fibers Preganglionic para sympathetic – Pterygopalatine gang. Postganglionic – lacrimal gland Sensory fibers to nasal & palatine glands Joins deep petrosal N – N to pterygoid canal

CONT..: 

CONT.. N to stapedius 6mm above SMF Supply stapedius Sensory auricular Br Joins auricular br of vagus Supply retro-auricular groove & concha

Chorda tympani : 

Chorda tympani 4mm above SMF Lat & ant to Facial N Passes b/w long process incus & upper part of handle of malleus 2 types of fibers Preganglionic parasympathetic – submandibular Ganglion Postganglionic – submandibular & sublingual gland Special sensory – ant 2/3 rd of tongue

CONT..: 

CONT.. Surgical importance: GSPN - landmark in middle cranial fossa approach CT – landmark in post tympanotomy CT – lat margin of facial recess CT – medial limit for facial ridge in CWD

Extratemporal region: 

Extratemporal region The stylomastoid foramen > medial aspect of mastoid tip > FN exit from SMF>below tympanic plate& L to the base of styloid > nonvascular area Lat to base of cartid sheath & behind the parotid gland. Post.auricular N( occ frontalis &muscles of pinna ) Muscular Brs (post belly of digastric & stylohyoid )

Terminal branches : 

Terminal branches Terminal branches: Temporal Zygomatic Buccal Mandibular Cervica

Cont..: 

Cont..

Cont..: 

Cont.. Temporal : Comes out through the upper pole of parotid gland Cross zygomatic arch Auricularis anterior & superior, frontalis orbicularis oculi & corrugator supercilii Zygomatic : Also called upper zygomatic Cross zygomatic bone Orbicularis oculi

Cont..: 

Cont.. Marginal mandibular : Comes out through the ant. Boarder of partid gland Runs 1-2cm below the inferior ramus of mandible Muscles of lower lip&chin ( Deperessor anguli oris ,Depressor labii inferioris,Mentalis ) Cervical : Comes out through the lower pole Supply platysma Buccal : 1 cm below zygomatic arch 2 in number runs along parotid duct

Cont..: 

Cont.. Buccal br :1.Upper deep buccal 2.Lower deep buccal Risorius (smirk) Buccinator (aids chewing) [LDB] Levator Labii Superioris Levator Labii Alaque Nasi (snarl) Levator Anguli Oris (soft smile) Nasalis (Flare Nostrils) Orbicularis Oris (Purse Lips)

Anatomical Relationship of FN in adult & children : 

Anatomical Relationship of FN in adult & children Child Adult Absent mastoid process & incomplete tympanic ring .CT may exit thru SMF 2 nd genu is more acute & lateral N trunk on exit from SMF is more anterior & lateral N very superficial over angle of mandible Presnt mastoid process & complete ring .CT exits separately prox to SMF 2 nd genu less acute & more medial Parotid is more post. N trunk is less anterior & deeper N superficial over angle of mandible

Blood Supply : 

Blood Supply AICA > Supply N in CP angle Intracranial/ Meatal : labyrinthine branches from ant inf cerebellar artery Geniculate&Perigeniculate : superficial petrosal branch of middle meningeal artery Tympanic/Mastoid: stylomastoid branch of posterior auricular artery

Facial nerve embryonic development: 

Facial nerve embryonic development Facial nerve course, branching pattern, and anatomical relationships are established during the first 3 months of prenatal life The nerve is not fully developed until about 4 years of age The first identifiable FN tissue is seen at the third week of gestation- facioacoustic primordium or crest

Facial nerve embryology: 4th week : 

Facial nerve embryology: 4 th week By the end of the 4 th week, the facial and acoustic portions are more distinct The facial portion extends to placode The acoustic portion terminates on otocyst

Facial nerve embryology: 7th week: 

Facial nerve embryology: 7 th week Early 7 th week, geniculate ganglion is well-defined and facial nerve roots are recognizable The nervus intermedius arises from the ganglion and passes to brainstem. Motor root fibers pass mainly caudal to ganglion

Facial nerve embryology: 7th week: 

Facial nerve embryology: 7 th week

Facial nerve embryonic development: Extratemporal segment - branches: 

Facial nerve embryonic development: Extratemporal segment - branches Proximal branches form first 6 th week, posterior auricular branch>branch of digastric Early 8 th week,temporofacial and cervicofacial divisions Late 8 th week, 5 major peripheral subdivisions present

Facial nerve embryonic development: Extratemporal segment – other nerves : 

Facial nerve embryonic development: Extratemporal segment – other nerves Facial nerve communicates with peripheral branches of CN V, IX, X, cervical cutaneous nerves greater auricular nerve and transverse cervical branches of the cervical plexus (C2, C3) Trigeminal nerve: auriculotemporal , infraorbital , buccal , mental branches All connections are complete by week 12 except for 4 (connections to branches of CN V at orbit periphery)-these are complete at 4.5 months

Peripheral communications of facial nerve : 

Peripheral communications of facial nerve

Facial nerve embryonic development: Extratemporal segment – Parotid : 

Facial nerve embryonic development: Extratemporal segment – Parotid

Surgical Landmarks : 

Surgical Landmarks Ear & mastoid surgery Geniculate ganglion lies superior to Processus cochleariformis 2 nd genu hugs inferior aspect of LSCC Facial N lies above OW niche Incus lies lateral to Facial N Facial N runs behind Pyramid Facial N lies 6-8mm inferior to Tympano Mastoid suture Digastric ridge – mastoid segment

Cont…: 

Cont… Parotid surgery Tragal pointer – 1cm deep&inf Tympanomastoid suture N lies lat to Styloid process Superficial to Retromandibular vein N bisects angle b/w Post belly of digastric & ear canal Buccal br I cm below&parallel to zygomatic arch

Variations : 

Variations MC variations Facial N displacements Dehiscence of fallopian canal Dehiscence in tympanic seg (35-55%)-mc Vertical seg variations Bipartite N Ant displaced N With post hump

Cont..: 

Cont.. Katz & Catalano classification: Type I (25%)no anastomic links bet the 2 branches Type II (14%) buccal branch subdivided Type III(44%) Type IV(14%) Type V(3%)

PowerPoint Presentation: 

Otology could be a dull way of life without the 7 th cranial N arrogantly swerving through the temporal bone to the muscles of facial expression “JOHN GROVES” THANK YOU