Facial nerve traumatic injury and repair
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The document discusses the anatomy and physiology of the facial nerve, as well as injuries and repair. It covers: - The gross anatomy and histology of the facial nerve as it traverses the temporal bone. - Classifications of facial nerve injuries including neuropraxia, axonotmesis, neurotmesis, and transection. - The degeneration and regeneration processes after injury, including changes in the proximal and distal nerve segments and target muscles. - Surgical techniques for nerve repair including fascicular repair, grafting, and principles such as achieving a tension-free repair. - Scales for assessing recovery after compression injuries or surgery, such as the House-B
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Facial nerve traumatic injury and repair
- 1. Facial Nerve Traumatic injury and repair
- 2. • Gross anatomy • Histology • injury classifications • Degeneration • Regeneration • Surgical nerve repair • recovery
- 3. General outline • Nuclei • Main Facial N and Intermediate N • Internal Auditory Meatus • Geniculate Ganglion • Intratemporal branches – Greater petrosal N – Stapedial N – Chorda Tympani • Stylomastoid Foramen • Extratemporal Branches – Posterior Auricular N – TZBMC
- 4. Facial Nerve • Traverses temporal bone in bony canal – fallopian canal • Begins at fundus of internal auditory canal (IAC), terminates at stylomastoid foramen • Lacks fibrous sheath in IAC, surrounded by a thin layer of arachnoid • Segments: – Labytinthine – Tympanic – Mastoid – Extracranial
- 5. Facial Nerve • Labyrinthine segment – First, shortest, narrowest – Superior to cochlea – Opens into geniculate fossa, located just deep to supratubal recess • Geniculate Ganglion – Formed by juncture of nervus inrermedius and facial nerve into a common trunk – 3 nerves • Greater superficial pertrosal nerve • Lesser petrosal nerve • External petrosal nerve – Secrotomotor fibers to lacrimal nerve – Lesser petrosal nerve secretory fibers to parotid
- 6. Facial Nerve • Tympanic segment – Occupies medial wall of anterior attic – Skims over superior aspect of cochleariform process – Forms superior wall of oval window niche posteriorly • 2nd Genu – At pyramidal eminence – To mastoid/vertical segment – Anteroinferior to lateral SCC – Anterior to line drawn through short process of incus
- 7. Facial Nerve • Mastoid / Vertical Segment – Variable course – Chorda tympani branch – Stapedial branch – Aponeurosis of Post belly of Digastric at stylomastoid foramen – Tympanomastoid Suture line
- 8. Extratemporal Course • Exits through SM Foramen, near origin of posterior belly of digastric m. • Branches: – Post Auricular – Temporal, Zygomatic, Buccal, Marginal Mandibular, Cervical • Divides into upper temperofacial and lower cervicofacial division
- 9. Peripheral branches • Posterior Auricular Nerve – Passes upwards behind ear – Supply • Auricularis Posterior • Occipital belly of frontalis • Muscular branch – Post belly of digastric – Stylohyoid
- 10. Intraparotid Branches… • Plexiform arrangement within parotid gland – pes anserinus • Superficial to retromandibular v and ECA • Temporal branches – Upper border of gland, crosses zygomatic arch – Supply: auricularis anterior & superior part of frontalis • Zygomatic branches – Crosses zygomatic arch and bone, lies directly on periosteum – Supply: orbicularis oculi
- 11. • Buccal branches – Close to parotid duct – Supply: Buccinator, nose, upper lip • Marginal mandibular branch – Runs forward along lower border of mandible – Passes superficial to facial A and V – No connection with other branches • Cervical branches – Supplies platysma
- 12. Variations on facial nerve anatomy
- 13. Function • Motor – Facial expression – Post belly digastric, stylohyoid – Stapedius • Parasympathetic – Chorda tympani: Submandibular & sublingual gland – Greater Petrosal N: Nasal mucosa & lacrimal gland via PtPal ganglion • Corneal Reflex (efferent limb) • Afferent – Taste from ant 2/3 tongue via chorda tympani to solitary nucleus – Auricle – Nervus intermedius
- 17. Histology
- 18. Degrees of facial nerve injuries • Sunderland’s classification (1978) • Seddon’s classification( 1943)
- 19. Neuropraxia (1st degree injury) • Physiologic neural block is created by increased intraneural pressure • Nerve will not conduct an impulse across site of compression • Nerve will respond to electric stimulation applied distal to lesion • Once compression relieved immediate return of muscle mvt or within 3 weeks
- 20. Axonotmesis (2nd degree injury) • Occurs if compression is not relieved • Obstruction of venous drainage with increased intraneural pressure • Results in axon damage • If process is reversed there will be complete gradual recovery provided there is no loss of endoneural tubes
- 21. Neurotmesis (3rd degree injury) • Intraneural pressure continues and loss of endoneural tubes • Marked reduction of response to electrical tests • Spontaneous recovery delayed and incomplete • Synkinesis
- 22. Transection (4th/5th degree injury) • Partial or complete transection of the nerve • Spontaneous recovery not expected • Recovery even under ideal conditions not good • Need surgical interventions
- 23. Degree of injury Pathology EEMG response % of normal Neural recovery Clinical recovery begins 1 Compression Damming of axoplasm 100 No morphologic changes noted 1 – 3 wks 2 Compression persists Increased intraneural pressure. Loss of axons 25 Axons grow into intact empty endoneural tubes at rate of 1mm/day 3 weeks to 2 months 3 Loss of endoneural tubes 0 – 10 New axons mix up and split, causing mouth mvts with eye closure and mass mvts (synkinesis) 2 – 4 months 4 Above plus disruption of perineurium 0 Axons blocked by scars, impairing regenerations 4 – 18 months 5 Complete transections 0 Complete disruption with scar filled gap. Barrier to regrowth and muscle innervation none
- 24. Histological changes in nerve injuries • Changes in axotomy 1st described by Franz Nissl for cells of facial neucleus • Chromatolysis and retrograde reaction or axonal reaction
- 25. Proximal segment • Degeneration occurs for a varying distance proximal to nerve injury • Closer the injury to cell body, and more traumatic, the worse the degree of injury proximally • Earliest regenerative response is seen within 24 hrs (rat)
- 26. • Within three days the proximal stump of the nerve begins to enlarge and form axonal sprouts • Once regeneration begins the rate of recovery can be estimated by measuring the distance between the site of injury and the region of denervated muscle • Decrease in diameter of axons. NB because it explains spontaneous decompression that occurs following degeneration of nerve
- 27. Proximal segment • Rate of nerve regeneration was stated by TINEL to be 1mm/day or 1in/month • Seddon’s figure 1.5 + 0.2mm/day • Tinel line can be traced along a cross facial nerve graft as it advances across the face
- 28. Distal segment • Undergoes Wallerian degeneration • Schwann cells proliferate and take on a phagocytic role, removing axonal and myelin debris • Occurs within 5 hours • Basal lamina of schwann cells provides the chemotactiv scaffolding for the advancing growth cone
- 29. Muscle end • Knowledge still incomplete • Following degeneration muscles atrophy progressively over a period of weeks to months • Denervation then stabilises for a varied and perhaps indefinite period of time, depending on completeness of the original lesion and the degree of spontaneous reinnervation
- 30. Cell body regeneration • Cell body begins regenerative process within 7 hours of nerve injury and is believed to persist indefinitely, providing cell body survives the initial injury • Poor results of late neural repair thus related to inability of the peripheral structures to regenerate after certain critical period following injury
- 31. Axon regeneration • Schwann cells also produce growth factors • Produce tubes through which new axons travel • Regenerating axons advance along the distal nerve segment eventually making contact with distal receptors
- 32. Axon regeneration • If regenerating axons do not reach channels provided by bunger bands within period of 3 to 4 months, the channels degenerate and replaced by connective tissue
- 33. Muscle • New NMJ formed after an injury far outnumber the original NMJ • Preselection mechanism appears to assure that the denervated muscles receive motor unit axons arising from the appropriate cell body • Eventually complete denervation will lead to atrophy of muscles and at some future time replaced by fibrous tissue
- 34. Response to injury • Increased of levels of cytokines is related to death of cell bodies • May be partially prevented by early suture repair of the nerve
- 35. Surgical repair • Surgeon suturing proximal to distal segment is suturing a proximal segment containing bundles of regenerating units to distal segment composed of schwaan cells • Grafting provides segment of nerve undergoing active wallerian degeneration with all the benefits of schwaan cells, without potential influence of distal receptors
- 36. Graft material • Usually cutaneous nerve segments from various body parts – Median antebrachial cutaneous nerve – Sural nerve – Greater auricular nerve – Cervical cutaneous nerve • Futuristic materials – Eg conduit repair
- 37. Principles of nerve repair • Microsurgical technique, including magnification and microsurgical instruments • A primary epineurial nerve repair with 9-0 or 10- 0 nylon sutures to minimise reactions • Nerve repair must be “tension free”, postural maneuvers such as neck turning to allow primary repair are discouraged • When tension free primary nerve repair is not possible, an interposition/interfascicular nerve graft recommended
- 40. Conduit repair • Only done in frog/toad models • 1st attempted in 1979 • Brogens demonstrated that negative voltage applied to injured nerve on a toad resulted in both stumps regenerating towards each other
- 41. Recovery post surgery • House brackmann scale guide for nerve compressions • RFNRS used to grade nerve recovery post resection and grafting Grade description 1 Normal function 2 Mild dysfunction, complete eye closure normal symmetry at rest 3 Moderate dysfunction, complete eye closure. Obvious assymetry at rest 4 Mod – severe dysfunction, incomplete eye closure, noticeable assymetry @ rest 5 Severe dysfunction, incomplete eye closure, only twitch of gross motor mvt 6 Total paralysis
- 42. Gardener-Robertson hearing classification for VIII nerve function
- 43. Repaired Facial Nerve Recovery Scale (RFNRS) Score Function A Normal nerve function B Independent movement of eyelids and mouth, slight mass motion, slight movement of forehead C Strong closure of eyelids and oral sphincter, some mass movement, no forehead movement D Incomplete closure of eyelids, significant mass motion, good tone E Minimal movement of any branch, poor tone F No movement
- 44. Two books to consider
Editor's Notes
- The facial nerve is composed of approximately 10,000 neurons, 7,000 of which are myelinated and innervate the nerves of facial expression. Three thousand of the nerve fibers are somatosensory and secretomotor and make up the nervus intermedius.. Main N – lower border of pons, above the olive Intermediate N – Between pons and inferior cerebellar peduncleThe facial nerve emerges from the brainstem with the nerve of Wrisberg, ie, the nervus intermedius (see the image below). The nervus intermedius gained its name from its position as it courses across the cerebellopontine angle (CPA) between the facial nerve and the vestibulocochlear nerves (ie, CN VII, CN VIII). The average distance between the point where the nerves exit the brainstem and the place where they enter into the internal auditory canal (IAC) is approximately 15.8 mm. The facial nerve and the nervus intermedius lie above and slightly anterior to CN VIII. The motor part - facial nerve nucleus in the pons the sensory part - nervus intermedius. The motor part and sensory part of the facial nerve enters the petrous temporal bone into the internal auditory meatus (intimately close to the inner ear) then runs a tortuous course (including two tight turns) through the facial canal, 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, it does not innervate the gland - CN IX, glossopharyngeal nerve. The facial nerve forms the geniculate ganglion prior to entering the facial canal
- The facial nerve travels through the petrous temporal bone, in a bony canal called the fallopian canal (after Gabriel Fallopius). No other nerve in the body travels such a long distance through a bony canal. Because of this bony shell around the nerve, inflammatory processes involving the central nervous system (CNS) and the facial nerve or traumatic injuries to the temporal bone can produce unique complications. CPA 15.8mm IAC 8-10mm LAB 3-5mm Tymp 11mm Mastoid 13mm Total length 60mm
- 3- 5mm longseparated from middle cranial fossa by a thin bone plate Fibrous sheath acquired at ganglion At: Facial hiatus – greater superficial petrosal N projects anteriorly along middle fossa floor first genu – main trunk turns posterior and slightly inferior, enters tympanic segment In this segment, the nerve is directed obliquely forward, perpendicular to the axis of the temporal bone, as shown above. The facial nerve and the nervus intermedius remain distinct entities at this level. The term labyrinthine segment is derived from the location of this segment of the nerve immediately posterior to the cochlea. The nerve is posterolateral to the ampullated ends of the horizontal and superior semicircular canals and rests on the anterior part of the vestibule in this segment. The labyrinthine segment is the narrowest part of the facial nerve and is susceptible to compression by means of edema. This is the only segment of the facial nerve that lacks anastomosing arterial cascades, making the area vulnerable to embolic phenomena, low-flow states, and vascular compression.
- Extends from geniculate ganglion to horizontal semicircular canal is abt 8-11mm Passes behind cochleariform process (important landmark for finding cnV!!) Second genu Is lateral and posterior to the pyramidal process Mastoid segment is longest part of intratemporal course of the facial nerve (during middle ear surgery facial nerve is most commonly injured at pyramidal turn)
- Second genu marks the beginning of mastoid segment. Corda tympani is terminal branch of nervus intermedius
- Travels btwn digastric and stylohuoid muscles and enters parotid. Sensory branch exists the nerve just below the stylomastoid foramen and innervates the posterior wall of ext auditory canal and portion of TM
- Topographic landmarks: line drawn bwtn the mastoid tip and angle of mandible(removal of parotid tissue inferior to this line can be performed easily) Frontal branch roughly located along a line extending from Surgical landmarks: tympanomastoid suture line, tragal pointer,
- Fx: wrinkling of forehead (Temporal branch) Fx: blinking (zygomatic branch)
- 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).
- The facial nerve is composed of approximately 10,000 neurons, 7,000 of which are myelinated and innervate the nerves of facial expression. Three thousand of the nerve fibers are somatosensory and secretomotor and make up the nervus intermedius. The course of the facial nerve and its central connections can be roughly divided into the segments listed in Table 1, below.
- Grade 1: compression without loss of structure; recovery is normal Grade 2: axon degeneration, regeneration is appropriate Grade 3: loss of endoneural tubes, recovery is incomplete with synkinesis Grade 4: disruption of perineurium, recovery is poor Grade 5: complete disruption no spontaneous recovery Grade 1- 3 can occur with viral inflammarory immune disorders such as bells, and herpes zoster cephalicus 4th and 5th grade occur when there is disruption of the nerve, eg transection in surgery, trauma or rapidly growing benign or malignant tumour Seddon classification only describes neurapraxia, axonotmesis and neurotmesis
- Degree of faulty regeneration directly proportional to the number of endoneural tubes that have been disrupted. Synkinesis is the result from miswiring of nerves after trauma. This result is manifested through involuntary muscular movementsaccompanying voluntary movements. For example, voluntary smiling will induce an involuntary contraction of the eye muscles causing the eye to squint when the subject smiles
- Synkinesis is the result from miswiring of nerves after trauma. This result is manifested through involuntary muscular movementsaccompanying voluntary movements. For example, voluntary smiling will induce an involuntary contraction of the eye muscles causing the eye to squint when the subject smiles.
- neurons are seen to have greatly increased numbers of cellular organelles, ribosomes either in free form or bound to endoplasmic reticulum.
- Proximal extent of the degeneration depends on two factors Proximity of the injury to the cell body Nature of injury Within three days proximal stump begins to enlarg Each nerve fiber develops into regenerating unit composed of many fivers At the tip of each of these fivers is a growth cone with multiple filopodia It is these filopodia that sample the neural environment Adhere to basal lamina of the schwann cells and advance the regenerating unit id distal direction Each axon sends out many growth cones, which have protein GAP43 as component of cell membrane Each growth cone has motile properties dependent on actin- myosin nteraction Growth cones advance alond the basement cell substrate of distal segment, corresponding to bands of BUNGER Concomittent neural fibroblast proliferation is seen,
- Within three days proximal stump begins to enlarg Each nerve fiber develops into regenerating unit composed of many fivers At the tip of each of these fivers is a growth cone with multiple filopodia It is these filopodia that sample the neural environment Adhere to basal lamina of the schwann cells and advance the regenerating unit id distal direction Each axon sends out many growth cones, which have protein GAP43 as component of cell membrane Each growth cone has motile properties dependent on actin- myosin nteraction Growth cones advance alond the basement cell substrate of distal segment, corresponding to bands of BUNGER Concomittent neural fibroblast proliferation is seen Kreutzberg and schubert noted that in 2 weeks after injury to peripheral portion of the facial nerve the diameter of proximal stump decreased by about 40%
- Tinel line is sensory testing, which relates to the fact that the all so called “pure” motor nerves contain many sensory afferent fibers from the muscles Assuming the injury is within the temporal bone, the distance can be estimated to be 14cm or 140mm, at an axon growth of 1mm per day an estimated 140 days would be required to regenerate one facial nerve fiber Thus under favourable condition return of facial nerve function should be noted in approx 4 months after intratemporal injury or repair of nerve Regenerative process of the facial nerve: rate of regeneration of fibers and their bifurcations. Kamijo Y, Koyama J, Oikawa S, Koizumi Y, Yokouchi K, Fukushima N, Moriizumi T. Source journal of neuroscience 2003 Department of Anatomy, Shinshu University School of Medicine, Matsumoto 390-8621, Japan.
- Leads to total absorption of the nerve and proliferation of the schwann cella Schwann cells become macrophages and engulf the debris of degeneation This process is so rapid that if it is not observed in the 1st 5 hours, degeneration appears to occur stimulaneously along the entire fiber First sign of degeneration is noticable within first 12 hours, and process is well advanced by 36 to 48 hours after injury Most of the debris of the myelination of the axon has been removed by 12/14 hours after injury, but some remnants have been reported 3months after the onset
- Axons reach distal stump through tubes formed by schwann cells Tubes multiply and are known as Bunger bands During acute phase of regeneration these tubes act as digestive chambers for lysis of myelin With regeneration new axon sprouts, finds their Modulation of this regeneration with support of fibers that have reached appropriate sensory/motor end organ and dieback of fibers that have reached inappropriate targets
- Schwann cells produce growth factors and tubes Regenerating axons advance along the distal nerve segment eventually making contact with distal receptors
- If two axons compete for one endplate, it has been shown that the appropriate axon will be successful. May account for excellent results noted with nerve repairs done shortly after injury.
- There are interesting correlation between response to neuronal injury and age of injured experimental animal. In general proximal nerve injuries in new and elderly mammals are associated with death of cell body.
- 15% elongation of nerve results in 78% of reduction in perfuision. Fibrin glue has shown to have no advantage other than mininmal time saving over standard techniques Laser techniques have been described but fallen out of favour over heat injury as well as inferior repair site tensile strength
- Recommendations clean epineurium 0.5mm and place sutures on the epineurium. In CPA place two or three sutures , at he brainstem one or two sutures, within the fallopian canal a nerve graft can be interposed without sutures if there is no chance of nerve end movement. Imagine facial nerve like a banana Skin of banana represents the epineurium, a thick tough covering Attempting to section a banana with the cover intact tends to crush the soft contents, Clean slice with out crushing is obtained by peeling back the banana skin Recommendations, strip epineurium both sides, and examine the fasicles and suture the epineurium with non absorbable, non traumatic sutures
- Fascicular repair possible, but very difficult as facial nerve only has between two or three fascicles Also depends on expertise of surgeon
- Housebrackmann grading 1 – 3 facial functions surgical decompression is possible for intrinsic facial nerve tumours
- Done for CPA tumours or trauma @ CPA level