Facial nerve 2 anatomy pathology management

Education

1. FACIAL NERVE

2. VII Cranial Nerve Mixed nerve with motor and sensory root Component of facial nerve includes: 1.Special visceral efferent (SVE Fibres) 2.General visceral efferent (GVE Fibres) 3.Special visceral afferent (SVA Fibres) 4.General somatic afferent (GSA Fibres)

3. Functional components and nuclei 1.SVE Fibres Arises from motor nucleus of FN in the pons Supply muscle of facial expression, auricular muscles, stylohyoid, posterior belly of digastric, and stapedius. 2.GVE Fibres Arises from lacrimatory and superior salivatory nuclei in brainstem Supplies secretomotor fibres to lacrimal,submandibular and sublingual glands

4. Functional components and nuclei 3.SVA Fibres Carries special sensation from anterior 2/3rd of tongue (except vallate papillae) via chordae tympani, soft and hardpalate via greater superficial petrosal nerve. Terminates in the nucleus tractus solitarius 4.GSA Fibres Carries general sensation from concha , posterosuperior part of external canal, and tympanic membrane. Terminate in the spinal nucleus of trigeminal nerve

5. Course and relations

6. Courses and relation Motor fibres arises from nucleus of 7th nerve,hook around nucleus of 6th nerve( Abducens nerve) and are joined by sensory root ( nerve of Wrisberg). This nerve consist of 2 distinct roots (at pontomedullary jn) Large medial motor root- Facial nerve proper Small lateral sensory root-nervosus intermedius

7. Courses and relation After emerging from BS root of facial nerve pass along with vestibulocochlear & labyrinthine artery travels through posterior cranial fossa and enters into Internal acoustic meatus At fundus of meatus, nerve enters bony facial canal, traverses the temporal bone and comes out of stylomastoid foramen. Here it crosses styloid process and divide into terminal branches

8. Course Course of FN divide into 3 parts 1.intra cranial part : from pons to IAM ( Internal Acoustic Meatus) 2.intratemporal part : from IAM to stylomastoid foramen Further divided into a)meatal segment : Within IAM b)labyrinthine segment c)tympanic(horizontal)segment d)mastoid(vertical)segment

9. Course 3.Extra cranial part : from SMF to termination of its peripheral branches

10. Labyrinthine segment ( SHORTEST SEGMENT OF NERVE) From fundus of meatus to geniculate ganglion where nerve takes a turn posteriorly forming a genu Nerve in this segment is narrowest in diameter Thus edema or inflammation can easily compress nerve and cause paralysis

11. Tympanic segment From geniculate ganglion to just above pyramidal eminence Lies above oval window and below lateral semicircular canal Mastoid segment From pyramid to SMF Between tympanic and mastoid segment-2nd genu of nerve

12. Branches Facial canal Greater petrosal nerve Nerve to stapedius Chorda tympani SMF Posterior auricular Nerve to stylohyoid Nerve to post belly of digastric IN FACE Temporal Zygomatic Buccal Marginal Cervical

13. Branches

14. Branches Greater superficial petrosal nerve Arises from geniculate ganglion Carries secretomotor fibres to lacrimal gland Communicating branch It joins auricular branch of vagus Supplies concha,retroauricular groove,posterior meatus and outer surface of TM

15. Branches Nerve to stapedius innervates the stapedius muscle,which plays a role in the auditory system by dampening sound transmission Arises from the level of second genu and supplies the stapedius muscle.

16. Branches Chorda tympani Arises from middle of mastoid segment Passes between incus and neck of malleus leave the tympanic cavity through petrotympanic fissure Carries Secretomotor fibres to submandibular and sublingual gland Brings taste from anterior ⅔ rd of tongue

17. Branches 5 terminal branches Nerve trunk after crossing styloid process forms 2 divisions Upper-temporofacial(temporal,zygomatic) Lower-cervicofacial(buccal,mandibular, Cervical) Supplies muscle of facial expression

18. Blood supply of FN Antero inferior cerebellar artery Supplies nerve in cerebellopontine angle Labyrinthine artery Branch of A nterior Inferior cerebellar artery Supplies nerve in internal auditory canal.

19. Blood supply of FN Superficial petrosal artery Branch of middle meningeal artery Supplies geniculate ganglion and adjacent region Stylomastoid artery Branch of posterior auricular artery Supplies mastoid and tymp segment

20. Variation and anomalies of FN Bony dehiscence (m/c) Dehiscence occurs m/c in tympanic segment above region of Oval window. A dehiscent nerve is prone to injury during surgery and easily involved in mastoid and middle ear infections Prolapse of nerve Dehiscent nerve may prolapse over stapes (makes stapes surgery/ ossicular reconstruction difficult)

21. Variation and anomalies of FN Hump Nerve may make hump posteriorly near hori. canal Making it vulnerable to injury while exposing antrum during mastoid surgery Bifurcation and trifurcation Vertical part of FN divide into 2 or 3 branches each occupying a seperate canal and exiting through individual foramen

22. Variation and anomalies of FN Bifurcation and enclosing the stapes Nerve divide proximal to OW-one part passing above and other below it and then reuniting Between ow and Rw Just before ow the nerve cross in mid ear passing b/w ow and rw

23. Thank you

24. SURGICAL LANDMARKS OF FACIAL NERVE For middle ear and mastoid surgery: Processus Cochleariformis : Demarcates geniculate ganglion which lies just anterior to it. Tympanic segment starts at this level. Oval window and horizontal canal : Facial nerve runs above oval window (stapes) and below horizontal canal. Short process of Incus : FN lies medial to shirt process of Incus at level of aditus. Pyramid : FN runs behind pyramid and posterior tympanic sulcus Tympanomastoid suture : ain vertical or mastoid segment FN runs behind the suture. Digastric Ridge : FN leaves mastoid at the anterior end of digastric Ridge.

25. For parotid surgery Cartilagenous pointer: FN lies 1cm deep and slightly anterior and inferior to pointer. It is a sharp triangular piece of cartilage of pinna and points to the nerve. Tympanomastoid suture: FN lies 6-8 mm deep to the suture. Styloid Process : The nerve crosses lateral to styloid Process Posterior belly of digastric: When post belly of digastric traced backwards along its upper border to its attachment to digastric groove nerve found to lie between it and styloid Process.