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facial nerve:neuroanatomy


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by humra shamim

Published in: Health & Medicine

facial nerve:neuroanatomy

  1. 1. Facial Nerve:Neuroanatomy by Humra shamim
  2. 2. 1. Introduction 2. Embryology 3. Nuclei of origin 4. Course & Relations 5. Branches of facial nerve 6. Ganglia associated with facial nerve 7. Blood supply 8. Disorders of facial nerve Contents
  3. 3.  The Facial nerve is the seventh of twelve paired cranial nerves, it is a mixed nerve with motor and sensory roots.  It emerges from the brain stem between the pons and the medulla, controls the muscles of facial expression  It functions in the conveyance of taste sensations from the anterior two thirds of the tongue and oral cavity  It also supplies preganglionic parasympathetic fibres to several head and neck ganglia Introduction
  4. 4. • It contains approx. 10,000 fibres out of which 7000 are carried by motor root and 3000 are sensory and parasympathetic (nerve of Wrisberg)
  5. 5. Embryology  The facial nerve is developmentally derived from the hyoid arch, which is the second branchial arch The motor division of facial nerve is derived from the basal plate of the embryonic pons The sensory division originates from the cranial neural crest
  6. 6. 3rd week • Facioaccoustic primordium develops giving raise to 7th and 8th cranial nerves • FIRST distinguishable feature of facial nerve
  7. 7. Facial nerve embryology: 4th week  By the end of the 4th week, the facial and acoustic portions are more distinct  The facial portion extends to placode  The acoustic portion terminates on otocyst
  8. 8. Facial nerve embryology: 5th week  Early 5th week, the geniculate ganglion forms from distal part of primordium  It separates into 2 branches: main trunk of facial nerve and chorda tympani
  9. 9. Facial nerve embryology: 6th week  Near the end of the 5th week, the facial motor nucleus is recognizable  The motor nuclei of VI and VII cranial nerves initially lie in close proximity.  The internal genu forms as metencephalon elongates and CN VI nucleus ascends
  10. 10. Facial nerve embryology: 7th week  Early 7th 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
  11. 11. 10th to 12th week • Facial nerve makes 2nd genu • Peripheral branches are completely developed
  12. 12. At term • Almost similar to that of adult • More superficial as the mastoid process is absent
  13. 13. Age 1 to 3 • Mastoid process develops • Nerve is displaced medially and inferiorly
  14. 14. Applied anatomy • Ritchers cartilage forms the bones of 2nd pharyngeal arch (stapes, styloid process, cornua of hyoid bone) • Any abnormality should prompt nerve damage • Facial canal is derived from ritchers cartilage
  15. 15. • Congenital atresia is associated with facial nerve palsy in 50% of cases
  16. 16. Treacher collins syndrome (mandibulo facial dysostosis) There is a set of typical symptoms within Treacher Collins Syndrome The OMENS classification was developed as a comprehensive and stage-based approach to differentiate the diseases. O; orbital asymmetry M; mandibular hypoplasia E; auricular deformity N; nerve development and S; soft-tissue disease
  17. 17. Facial Nerve involvement in Treacher collins syndrome N0: No facial nerve involvement N1: Upper facial nerve involvement (temporal or zygomatic branches) N2: Lower facial nerve involvement (buccal, mandibular or cervical) N3: All branches affected
  18. 18. Goldenhars syndrome (oculoauriculo vertebral dysplasia) It is a wide spectrum of congenital anomalies that involves structures arising from the first and second branchial arches. Features of hemi facial microsomia, anotia, vertebral anomalies, congenital facial nerve palsy.
  19. 19. Cardiofacial Syndrome Unilateral facial paralysis involving only the lower lip and congenital heart disease  The facial paralysis in these patients involves only those muscles concerned with pulling the lower lip downwards and outwards  These are the mentalis, depressor labii inferioris and depressor anguli oris muscles
  20. 20. All are supplied by the mandibular marginal branch of the facial nerve The paralysis is only recognizable when the patient talks, smiles or cries
  21. 21. Moebius syndrome (congenital facial diplegia)  Abnormal VI ,VII,XII Nerve nuclei  Facial Nerve absent / smaller  Congenital Extra ocular muscle & facial palsy Congenital Facial nerve palsy
  22. 22. Diff between adults and children child adult 1. Absent mastoid process and incomplete tympanic ring 2. Chorda tympani exits through stylomastoid foramen 3. Second genu is very acute and lateral 4. When exits from stylomastoid foramen is more anterior 5. Nerve superficial over angle of the mandible 1. Matoid process and ring is complete 2. Chorda tympani exits proximal to stylomastoid foramen 3. Less acute and medial 4. Due to parotid it is less anterior 5. Less superficial
  24. 24. Facial nerve nuclei components • Branchiomotor (main motor) • Visceromotor (supra salivatory nucleus) • Special sensory ( tractus solitarius) • General sensory (upper part of spinal nucleus of trigeminal nerve)
  25. 25. 1 .1 Motor nucleus of facial nerve (SVE): It lies in the lower part of the pons
  26. 26. 2. Superior salivatory nucleus (GVE): It lies in the pons lateral to the main motor nucleus of VII and gives rise to secretomotor parasympathetic fibers that pass in greater superficial petrosal nerve and chorda tympani.
  27. 27. 3. Nucleus solitarus (SVA): It lies in the medulla, receives the taste sensation from the anterior 2/3 of the tongue via the central processes of the cells of the geniculate ganglion of the facial nerve
  28. 28. 4. GSA fibers : Through these, fibers to acoustic meatus & back of auricle through communication from auricular branch of vagus. These fibers terminate in main sensory nucleus & spinal nucleus of 5 th nerve
  29. 29. • Motor component forms the largest component of facial nerve nuclei • The other 3 components form a distinct facial sheath called nervus intermedius
  30. 30. Remember!! • The sensory fibres have their cell bodies in the geniculate ganglion • They are bipolar • One arm extending to periphery • Other arm extending to the pons
  31. 31. Course Of The Facial Nerve
  32. 32. Course of the facial nerve Has six segments • Intracranial segment • Intratemporal segment Meatal segment Labrynthine segment Tympanic segment Mastoid segment • Extratemporal segment
  33. 33. Intracranial segment (23 to 24mm) • From pons to internal acoustic meatus • Motor fibres loop over the abducens nerve forming facial colliculus in the floor of the fourth ventricle • Joined by the nervus intermedius • Together with 8th nerve cross CP angle • Lies ventral to 8th nerve
  34. 34. Applied anatomy • Intracranial portion lacks epineurium • Regained once it enters facial canal • surgery within the CP angle (schwannoma) makes the nerve vulnerable for iatrogenic injury and makes it difficult to identify it during dissection of a schwannoma as there is no connective tissue element separating it from the tumour
  35. 35. Meatal segment (8 to 10mm) • IAC to meatal foramen • Located anterosuperior to vestibulo cochlear nerve • Superior to crista transversa /falciform crest and anterior to crista verticalis ( bills bar) • NO branches
  36. 36. Applied anatomy • Within the meatus, the facial nerve has no separate sheath, but shares dural investment with the nervus intermedius and the vestibulocochlear nerve and is bathed in cerebrospinal fluid (CSF), again making it vulnerable to surgical manipulation.
  37. 37. Labrynthine segment (3 to 5 mm) • Shortest division • From entry of facial canal up to the genu • Susceptible to vascular injury • Enters the facial canal between cochlea and vestibule and runs posteriorly
  38. 38. Applied anatomy • The periosteum is thicker here than the entire facial canal • This should be cut if decompression to be performed • There are no anastomosing arterial arcades in this area and it is the part of the facial nerve most vulnerable to ischaemia. Owing to its bottleneck-like anatomical nature, it is also the part of the facial nerve that most probably suffers from ischaemia in the event of oedema following trauma or inflammation
  39. 39. Applied anatomy • During a translabyrinthine approach the labyrinthine segment is at risk while drilling along the superior semicircular canal • The labyrinthine segment is also that part of the facial nerve most likely to be injured in temporal bone fractures.
  40. 40. In the facial canal • Longest bony canal of any nerve • Occupies 73% of the bony canal • Nerve makes an acute turn of 40 to 80 degree Applied anatomy First genu being formed due to the pushing of the otic capsule (app anatomy)
  41. 41. Tympanic segment ( 8 to 11 mm) • NO branches • Lies beneath the LCC in the medial wall of the middle ear • Passes behind the oval window and the promontory
  42. 42. • Passes posterior to the cochleariform process , tensor tympani, and oval window • Just distal to pyrimidal eminence it makes a second turn ( second genu) passing vertically downward as the mastoid segment
  43. 43. Applied anatomy • Nerve may prolapse against the arch of stapes • Bifurcate around stapes • Course below the oval window • More acute turn, susceptible to injury in antrotomy
  44. 44. Applied anatomy • Bony wall of the tympanic segment is dehiscent in 35 to 55% of cases • ASOM in children and neonates present with facial nerve neuropraxia
  45. 45. Mastoid segment (10 to 14 mm) • Extends to the stylomastoid foramen with 3 branches • Nerve to stapedius • Chorda tympani • Nerve from the auricular branch of the vagus nerve ( pain fibres from the posterior part of the external acoustic meatus
  46. 46. Applied anatomy • Normal function of stapedius in congenital facial palsy • Animal studies show separate neurons other than main motor nucleus
  47. 47. Applied anatomy • Referred otalgia in bells palsy, vesicular eruption in herpes zoster due to sensory function in ear
  48. 48. Chorda tympani nerve  It arises from the facial nerve 6 mm above the stylomastoid foramen and runs upwards to perforate the posterior bony wall of the tympanic cavity.  It then passes forwards on the medial surface of the tympanic membrane between its fibrous and mucous layers crossing the handle of the malleus.
  49. 49. • Comes out through petrotympanic fissure to infratemporal fossa • Joins the lingual nerve • Through lingual nerve it supplies secretomotor fibres to submandibular ganglion • Taste fibres from anterior 2/3 of the tongue
  50. 50. At the exit from the stylomastoid foramen 1- Posterior auricular nerve: to the auricularis posterior and the occipital belly of the occipitofrontalis muscle. 2- Digastric branch: to the posterior belly of digastric muscle 3- Stylohyoid branch: to the stylohyoid muscle
  51. 51. Extra temporal segment • Passes between posterior belly of digaastric and stylohyoid muscles and enters the parotid gland • Lies between superficial and deep lobes of the gland • From the anterior border of the gland 5 branches emerge
  52. 52. Terminal branches
  53. 53. The temporal branches of the facial nerve (frontal branch of the facial nerve) crosses the zygomatic arch to the temporal region, supplying the auricularis anterior and superior, and joining with the zygomaticotemporal branch of the maxillary nerve, and with the auriculotemporal branch of the mandibular nerve. TERMINAL BRANCHES
  54. 54. The zygomatic branches of the facial nerve (malar branches) run across the zygomatic bone to the lateral angle of the orbit. Here they supply the Orbicularis oculi, and join with filaments from the lacrimal nerve and the zygomaticofacial branch of the maxillary nerve.
  55. 55. The Buccal Branches of the facial nerve (infraorbital branches), of larger size than the rest of the branches, pass horizontally forward to be distributed below the orbit and around the mouth.
  56. 56. MUSCLE ACTION Risorius Smile Buccinator Aids chewing by holding cheeks flat Levator Labii Superioris Elevates upper lip Levator labii superioris alaeque nasi Snarl Levator Anguli Oris Soft smile Nasalis Flare Nostrils Orbicularis oris muscle Purse Lips Depressor Septi Nasi Depresses Nasal Septum Procerus Moves Skin of Forehead The buccal branch supplies these muscles
  57. 57.  The marginal mandibular branch of the facial nerve passes forward beneath the platysma and depressor anguli oris.  It supplies the muscles of the lower lip and chin, and communicating with the mental branch of the inferior alveolar nerve.
  58. 58.  The cervical branch of the facial nerve runs forward  It forms a series of arches across the side of the neck over the suprahyoid region.  One branch descends to join the cervical cutaneous nerve from the cervical plexus; others supply the Platysma. Also supplies the depressor anguli oris.
  59. 59. Applied anatomy • Mandibular branch in 20% 2cm below mandible in submandibular area can lead to paralysis of mouth depressors • Temporal branch is superficial to aponeurotic system over the zygomatic arch, (hence at risk during surgery )
  60. 60. GANGLIAASSOCIATED WITH THE FACIAL NERVE Geniculate ganglion Submandibular ganglion Pterygopalatine ganglion
  61. 61. Geniculate Ganglion The geniculate ganglion (from Latin genu, for "knee") is an L- shaped collection of fibers and sensory neurons of the facial nerve located in the facial canal of the head. It receives fibers from the motor, sensory, and parasympathetic components of the facial nerve and sends fibers that will innervate the lacrimal glands, submandibular glands, sublingual glands, tongue, palate, pharynx, external auditory meatus, stapedius, posterior belly of the digastric muscle, stylohyoid muscle, and muscles of facial expression.
  62. 62. Submandibular Ganglion  The submandibular ganglion is small and fusiform in shape. It is situated above the deep portion of the submandibular gland, on the hyoglossus muscle, near the posterior border of the mylohyoid muscle.  The ganglion 'hangs' by two nerve filaments from the lower border of the lingual nerve (itself a branch of the mandibular nerve, CN V3). It is suspended from the lingual nerve by two filaments, one anterior and one posterior. Through the posterior of these it receives a branch from the chorda tympani nerve which runs in the sheath of the lingual nerve.
  63. 63. Pterygopalatine Ganglion The pterygopalatine ganglion (meckel's ganglion, nasal ganglion or sphenopalatine ganglion) is a parasympathetic ganglion found in the pterygopalatine fossa. It's largely innervated by the greater petrosal nerve (a branch of the facial nerve); and its axons project to the lacrimal glands and nasal mucosa
  64. 64. Central connections
  65. 65. Motor circuit
  66. 66. Secretomotor circuit
  67. 67. Facial Nerve: Functional Components  Special Visceral Efferent/Branchial Motor  General Visceral Efferent/Parasympathetic  General Sensory Afferent/Sensory  Special Visceral Afferent/Taste
  68. 68. 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) through 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
  69. 69. Superior salivatory nucleus nervus intermedius chorda tympani joins lingual nerve submandibular ganglion postganglionic parasympathteic fibers submandibular and sublingual glands
  70. 70. Special Visceral Afferent/Taste Postcentral gyrus nucleus tractus solitarius nervus intermedius geniculate ganglion chorda tympani joins lingual nerve anterior 2/3 tongue, soft and hard palate
  71. 71. Extratemporal part of the facial nerve • Tragal pointer: nerve is identified 1 cm inferior and deep to this • Posterior belly of digastric muscle : at its insertion to mastoid process nerve exits stylomastoid foramina anterior to it
  72. 72. Blood supply
  73. 73. Facial Nerve blood supply The facial nerve gets it’s blood supply from 4 vessels: Anterior inferior cerebellar artery – at the cerebellopontine angle Labyrinthine artery (branch of anterior inferior cerebellar artery) – within internal acoustic meatus Superficial petrosal artery (branch of middle meningeal artery) – geniculate ganglion and nearby parts
  74. 74. Stylomastoid artery (branch of posterior auricular artery) – mastoid segment Posterior auricular artery supplies the facial nerve at & distal to stylomastoid foramen Venous drainage parallels the arterial blood supply
  75. 75. Applied anatomy • The Labrynthine portion does not have any overlap • Petrosal artery alone • More vulnerable for ischemia
  76. 76. Applied anatomy • Recurrent paralysis may be due to sudden compressiion and decompression by a tumor like vestibular schwannoma • In vestibular schwannomas only 10% of facial neurons are required for normal facial function • Vestibular schwannomas rarely present with facial weakness • Presence of facial weakness facial schwannoma to be ruled out
  77. 77. Disorders of Facial Nerve 1. Supra nuclear type: Features: a) Paralysis of lower part of face (opposite side) b) Partial paralysis of upper part of face c) Normal taste and saliva secretion d) Stapedius not paralysed Facial Nerve Lesions
  78. 78. 2. Nuclear type: Features: a) Paralysis of facial muscle (same side) b) Paralysis of lateral rectus c) Internal strabismus
  79. 79. b) Injury distal to geniculate ganglion Features: i. Complete motor paralysis (same side) ii. No hyper acusis iii. Loss of corneal reflex iv. Taste fibers affected v. Facial expression and movements paralysed vi. Pronounced reaction of degeneration
  80. 80. Lesion distal to geniculate ganglion
  81. 81. c) Injury at stylomastoid foramen • Condition known as Bell’s Palsy
  82. 82. Background of BELL’S PALSY First described more than a century ago by Sir Charles Bell Yet much controversy still surrounds its etiology and management . Bell palsy is certainly the most common cause of facial paralysis worldwide
  83. 83. Demographics of Bells palsy Race: slightly higher in persons of Japanese descent. Sex: No difference exists Age: highest in persons aged 15-45 years. Bell palsy is less common in those younger than 15 years and in those older than 60 years.
  84. 84. Pathophysiology of Bells palsy Main cause of Bell's palsy is latent herpes viruses (herpes simplex virus type 1 and herpes zoster virus), which are reactivated from cranial nerve ganglia Polymerase chain reaction techniques have isolated herpes virus DNA from the facial nerve during acute palsy
  85. 85. Inflammation of the nerve initially results in a reversible neurapraxia Herpes zoster virus shows more aggressive biological behaviour than herpes simplex virus type1 Bell's phenomenon is the upward diversion of the eye ball on attempted closure of the lid is seen when eye closure is incomplete.
  86. 86. I. Unilateral involvement II. Inability to smile, close eye or raise eyebrow III. Whistling impossible IV. Drooping of corner of the mouth V. Inability to close eyelid (Bell’s sign) VI. Inability to wrinkle forehead VII. Loss of blinking reflex VIII. Slurred speech IX. Mask like appearance of face X. Loss/ alteration of taste Features of Bell’s Palsy
  87. 87. Diagnosis of Bells palsy By exclusion Criteria Paralysis or paresis of all muscle groups of one side of the face Sudden onset Absence of signs of CNS disease Absence of signs of Ear disease
  88. 88. Medical treatment Corticosteroids : Prednisolone 1 mg/kg/day 7-10 days Corticosteroids combine with antiviral drug is better Acyclovir 400 mg 5 times/day Famciclovir and valacyclovir 500 mg bid
  89. 89. Surgical treatment Facial nerve decompression Indication: Completely paralysis ENoG less than 10% in 2 weeks Appropriate time for surgery is 2-3 weeks after paralysis
  90. 90. It focuses on protecting the cornea from drying and abrasion due to problems with lid closure and the tearing mechanism. Lubricating drops should be applied hourly during the day and a simple eye ointment should be used at night. Eye care
  91. 91. Treatment consists of Infra-red radiation on affected side of the face at 2 ft (60cm) ,followed by interrupted galvanism on affected side Treatment was given daily at first few weeks & later thrice weekly. All patients are instructed to massage the face daily There is general agreement that 70-80% of these patients recover completely,while the reminder develop various sequelae within one to three months
  92. 92. Bibliography • Scott-Browns Otorhinolaryngeology, Head and Neck Surgery, 8th edition, Miachel Gleeson etal CRC press publication • Endoscopic ear surgery-Prisutti,Livio. • Grays Anatomy, 40th edition The Anatomical basis of Clinical practice, Susan Standring, Churchill Livingstone Elsivier publications • Clinical Neuroanatomy, 7th edition, Richard S. Snell, Lippincott Williams and Wilkins publications • McMinns and Abraham’s clinical atlas of human anatomy,7th edition. • K.J. Lee’s Essential Otolaryngeology, Head and Neck Surgery 10th edition McGrawHill publications
  93. 93. Thank you