Facial Nerve Trauma Simplified PDF

+ FACIAL NERVE TRAUMA + FACIAL NERVE ANATOMY AND PHYSIOLOGY + Facial Nerve Anatomy INTRACRANIAL SEGMENT: from the brainstem to the internal auditory canal 15.8 mm two components: 1. Motorroot 2. Nervus intermedius – carries preganglionic...

+ FACIAL NERVE TRAUMA + FACIAL NERVE ANATOMY AND PHYSIOLOGY + Facial Nerve Anatomy INTRACRANIAL SEGMENT: from the brainstem to the internal auditory canal 15.8 mm two components: 1. Motorroot 2. Nervus intermedius – carries preganglionic parasympathetic fibers and special afferent sensory fibers - Both join at the CPA/IAC to form the common facial nerve  Motor Nucleus in caudal portion of the ventrolateral pontine tegmentum. + Its axons take an unusual course, traveling dorsally and looping around the abducens nucleus, then traveling ventrally to exit the ventral pons medial to the spinal trigeminal nucleus. + Facial nerve motor, sensory and secretory motor nuclues + Facial nerve enter IAC + Facial nerve from brainstem to IAC + IAC and bill’s bar + Facial nerve in IAC + Facial Nerve Anatomy INTRATEMPORAL SEGMENTS Meatal – from porus acusticus to the meatal foramen of IAC – Travels in the anterior superior portion of the IAC (7-UP, 8-Down) » Posterior superior – superior vestibular nerve » Posterior inferior – inferior vestibular nerve » Anterior inferior – cochlear nerve Labyrinthine – From fundus to the geniculate ganglion – Runs in the narrowest portion of the IAC (0.68mm in diameter) – Greater superficial petrosal nerve comes off at this point Tympanic – Runs from geniculate ganglion to the second genu – Highest incidence of dehiscence here (25-55% of population) Mastoid – From second genu to stylomastoid foramen – Gives off branches to the stapedius muscle and the chorda tympani + + + Segment Location Length (mm) Supranuclear Cerebral cortex NA Brainstem Motor nucleus of facial nerve, NA superior salivatory nucleus of tractus solitarius Meatal segment Brainstem to internal auditory 13-15 canal (IAC) Labyrinthine Fundus of IAC to facial hiatus 3-4 segment Tympanic Geniculate ganglion to pyramidal 8-11 segment eminence Mastoid Pyramidal process to stylomastoid 10-14 segment foramen Extratemporal Stylomastoid foramen to pes 15-20 segment anserinus + + Facial Nerve Anatomy Extratemporal Segments exits stylomastoid foramen – Postauricular nerve - external auricular and occipitofrontalis muscles – Branches to the posterior belly of the digastric and stylohyoid muscles Enters parotid gland splitting it into a superficial and deep lobe Pes Anserinus – Branching point of the extratemporal segments in the parotid – To Zanzibar By Motor Car » Temporal » Zygomatic » Buccal » Marginal mandibular » Cervical + + Facial Nerve Components – Motor Supplies muscles of facial expression Stylohyoid muscle Posterior belly of digastric Stapedius muscle Buccinator – Sensory Taste to anterior 2/3 of the tongue Sensation to part of the TM, the wall of the EAC, postauricular skin, and concha – Parasympathetic Supplies secretory control to lacrimal gland and some of the seromucinous glands of the nasal and oral cavities Chorda tympani carries parasympathetics to the submandibular and sublingual glands + NERVE INJURY: CLASSIFICATION + Components of a Endonerium – Nerve 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 + Sunderland Nerve Injury Classification + Sunderland Nerve Injury Classification – Class I (Neuropraxia) Conduction block caused by cessation of axoplasmic flow What one experiences when their leg “falls asleep” Full recovery – Class II (Axonotmesis) Axons are disrupted Wallerian degeneration occurs distal to the site of injury Endoneural tube still intact Full recovery expected – Class III (Neurotmesis) Neural tube is disrupted Poor prognosis If regeneration occurs, high incidence of synkinesis (abnormal mass movement of muscles which do not normally contract together) + Sunderland Nerve Injury Classification Class IV Epineurium remains intact Perineurium, endoneurium, and axon disrupted Poor functional outcome with higher risk for synkinesis Class V Complete disruption Little chance of regeneration Risk of neuroma formation + Facial Nerve Trauma - Overview - Second most common cause of FN paralysis behind Bell’s Palsy - Represents 15% of all cases of FN paralysis - Most common cause of traumatic facial nerve injury is temporal bone fracture + Temporal Bone Fracture – 5% of trauma patients sustain a temporal bone fracture – Three types (Ulrich 1926 classification) » Longitudinal Most common type – 70-80% Fracture line parallel to long axis of petrous pyramid Secondary to temporoparietal blunt force EAC and TM laceration Results in facial nerve paralysis in 15-20% of cases » Transverse 10-20% of fractures Fracture line perpendicular to long axis of petrous pyramid Secondary to frontal or occipital blow, intact EAC Results in facial nerve paralysis in 50% of cases » Mixed 10% of temporal bone fractures + Longitudinal Transverse fracture fracture 1. Bleeding from external canal 1. Sensorineural hearing loss due to damage to 8th cranial due to laceration of skin and nerve ear drum 2. Haemotympanum 2. Fractures involving the bony (conductive deafness) portion of external canal 3. Facial palsy due to damage of 3. Ossicular chain disruption facial nerve causing conductive deafness. 4. Facial palsy (rare) 20% 4. Vertigo usually at the level of 5. Labyrinthitis ossificans (this horizontal segment distal to should be borne in mind geniculate ganglion before performing cochlear implant in these pts) 5. CSF otorrhoea (usually temporary) 6. Sensorineural hearing loss can occur due to consussion +  Kelly and Tami classification + + + + CT scan: transverse fracture + CT scan: longitudinal fracture + CT scan: complex fracture + Penetrating Trauma -Typically results in FN injury in the extratemporal segments -Gun shot wounds cause both intratemporal and extratemporal injuries GS wounds to temporal bone result in FN paralysis in 50% of cases Mixture of avulsion and blunt trauma to different portions of the nerve Much worse outcome when comparing GS related paralysis to TB fracture related paralysis + Iatrogenic Facial nerve – Surgical Trauma Most common is parotidectomy Most common otologic procedures with FN paralysis: – Mastoidectomy – 55% – Tympanoplasty – 14% – Exostoses removal – 14% – Mechanism : direct mechanical injury or heat generated from drilling – Most common area of injury - tympanic portion due to its high incidence of dehiscence in the this area, and its relation to the surgical field Unrecognized injury during surgery in nearly 80% of cases – Birth trauma Forceps delivery with compression of the facial nerve against the spine + Work-up: History History Mechanism – recent surgery, facial/head trauma Timing – progressive loss of function or sudden loss Transected nerve -> sudden loss Intraneural hematoma or impengiment -> progressive loss (better prognosis) Associated symptoms – hearing loss ,vertigo  + Work-up: Physical Physical Examination – full head and neck examination – Facial asymmetry – Signs of facial injury: lacerations, hematomas, bruising – Exam head/scalp for signs of injury to help guide you to vector of force if head trauma is involved – Otoscopic examination is a must Canal lacerations or step-offs deformity Hemotympanum, TM perforation, drainage of blood or clear fluid from middle ear Tuning fork tests help to determine any hearing loss + Clinical facial nerve test Facial movement: Temporal branches: Wrinkle forehead Elevate eyebrow Zygomatic branches: Close the eyes Mandibular branches: Show teeth Blow cheek Cervical grimacing + House-Brackmann Grading I. System Grade Characteristics Normal facial function in all areas II. Mild dysfunction Slight weakness noticeable on close inspection Forehead - Moderate-to-good function Eye - Complete closure with minimal effort Mouth - Slight asymmetry III. Moderate dysfunction Obvious but not disfiguring difference between the two sides -First time you can notice a difference at rest Forehead - Slight-to-moderate movement Eye - Complete closure with maximum effort Mouth - Slightly weak with maximum effort IV. Moderately severe dysfunction Obvious weakness and/or disfiguring asymmetry -First time you have incomplete eye closure Forehead – No motion -No forehead movement Eye - Incomplete closure Mouth - Asymmetric with maximum effort V. Severe dysfunction Only barely perceptible motion At rest, asymmetry Forehead – No movement Eye - Incomplete closure Mouth - Slight movement VI. Total paralysis No movement + Work-up: Radiologic Tests HRCT scans Bony evaluation Locate middle ear, mastoid, and temporal bone pathology Gadolinium enhanced MRI Rarely done in traumatic facial nerve injury better visualisation of soft tissue condition + Facial Nerve Testing to assess the degree of electrical dysfunction Can pinpoint the site of injury Helps determine treatment Can predict recovery of function – partial paralysis is a much better prognosis than total paralysis two categories: – Topographic test – Electrodiagnostic test + Facial Nerve Testing Topographic test Tests function of specific facial nerve branches Determine the site of facial nerve injury Do not predict potential recovery of function Schimer’s test Stapedial reflex Taste test Submandibular salivary flow test + Topographic test Lesion at nucleus in pons : Only motor fx affected No taste,lachrymation salivation disturbance no loss of stapedial reflex Lesion in CPA/IAM/labyrinthine segment: Impaired lachrymation, stapedial reflex , taste and salivation Lesion between geniculate ganglion and nerve to stapedius: Intact lachrymation Impaired stapedial reflex and taste + Topographic test Lesion between the nerve to stapedius and chorda tympani: Intact lachrymation and stapedial reflex Impaired taste Lesion below level of chorda tympani: Pure motor deficit Intact lachrymation, stapedial reflex, salivation and taste + + Schimer’s test The eye is gently dried of excess tears or topical LA The filter paper is folded 5 mm from one end The folded tip is inserted into the lower lid – at the junction of the middle and outer thirds of the lower lid – taking care not to touch the cornea or lashes. Thepatient is asked to keep their eyes closed for the duration of the test. After 5 minutes, the filter paper is removed and the amount of wetting from the fold is measured. + Schimer’s test GENERAL INTERPRETATION: Normal which is ≥15 mm wetting of the paper after 5 minutes. Mild which is 14-9 mm wetting of the paper after 5 minutes. Moderate which is 8-4 mm wetting of the paper after 5 minutes. Severe which is 25% is significant(positive schimmer test) + Stapedial reflex Part of audiometric evaluation for all patient with facial nerve weakness Accomplished at the time of impedance testing + Stapedial reflex Loud sound directed to either ear cause bilateral contraction of the stapedius muscle Normally 75-95db above the threshold Afferent: ME, cochlea, VIII n Efferent: VII n Provide diagnostic information of cochlear, retrocochlear and brainstem pathology + Both ipsilateral and contralateral are measured Normal ipsilateral: intact intergrity of reflex arch of the tested ear Normal contralateral: implies intact afferent and brainstem pathway of tested ear and intact efferent of contralateral ear. In VII n palsy: Absent :the site of injury most likely between geniculate ganglion and nerve to stapedius Present; injury site is distal to nerve to stapedius. + Right VII n + Cochlear pathology + Vestibulocochlear nerve pathology + Severe middle ear pathology + Brainstem pathology + Testing taste sweet, salt, sour and bitter taste are tested along the lateral margin of anterior 2/3 toward tip oftongue. Patient must not retract the tongue in Electrogustometry: Electrical method Small current applied to lateral border of anterior 2/3 of tongue Current slowlt increase until patient able to perceive the metallic taste Normal threshold: 1 mA 4 mA in chorda tympani involvement + Submandibular gland flow Sialometry UnderLA: small polythene tube passed into Wharton’s duct Salivation induced by stimulus of 6% citric acid on the anterior tongue. Drops of saliva from each side is mesured and compared + Electrodiagnostic test Utilize electrical stimulation to assess nerve conductivity/function Most commonly used today Able to demonstrate evidence of degeneration as early as 3 days after onset Common tests: Nerve excitabillity test Maximal stimulation Electroneuronography electromyography + Nerve Excitability Test (NET) Compares amount of current required to illicit minimal muscle contraction - normal side vs. paralyzed side How it is performed: A stimulating electrode is applied over the stylomastoid foramen DC current is applied percutaneously Face monitored for movement The electrode is then repositioned to the opposite side, and the test is performed again A difference of 3.5 mA or greater between the two sides is considered significant Drawback - relies on a visual end point (subjective) + Maximal Stimulation Test (MST) Similar to the NET, except it utilizes maximal stimulation rather than minimal Usually >5 mA The paralyzed side is compared to the contralateral side Not accurate if done within 72 hours Comparison rated as equal, slightly decreased, markedly decreased, or absent – Equal or slightly decreased response = favorable for complete recovery – Markedly decreased or absent response = advanced degeneration with a poor prognosis Drawback – Subjective + Electroneurography (ENoG) Considered the most accurate of the electrodiagnostic tests How it works: Bipolar electrodes deliver an impulse to the FN at the stylomastoid foramen Summation potential is recorded by another device placed at nasolabial region Stimulus gradually increased until there is no further increase in the respond amplitude The peak to peak respond amplitude is proportional to number of intact axons The two sides are compared as a percentage of response 90% degeneration – surgical decompression should be performed Less than 90% degeneration within 3 weeks predicts 80 - 100% spontaneous recovery Disadvantages: discomfort, cost, and test-retest variability + + PPUKM ENoG lab + Electromyography Determines the activity of the muscle itself How it works – Needle electrode is inserted into the muscle, and recordings are made during rest and voluntary contraction Normal = biphasic or triphasic potentials Demonstrate the signs of recovery 10-21 days post injury - fibrillations 6-12 weeks prior to clinical return of facial function – polyphasic potentials are recordable Does not require comparison with normal side Not helpful of recent onset injury: Showed denervation potential only after 8-10 days + myography + FACIAL NERVE TRAUMA: Surgery + General surgical guideline Reconstruction: Dynamic: surgical procedures that enable the patient to actively move facial or grafted muscles Static :nclude operations performed to optimize symmetry and reduce complications : lip wedge resection, sling placement, partial cervicofacial rhytidectomy, upper lid blepharoplasty, lateral canthopexy). When decided for surgery: informed consent and preoperative consult are important Must inform: patient’s face will never be symmetrical or have a normal balance  + General surgical Iatrogenic Injury guideline If transected during surgery – Explore 5-10mm of the involved segment – Stimulate both proximally and distally Response with 0.05mA = good prognosis; further exploration not required If only responds distally = poor prognosis, and further exposure is warranted If loss of function is noted following surgery, wait 2-3 hours and then re- evaluate the patient. This should be ample time for an anesthetic to wear off – Waited time and still paralysis Unsure of nerve integrity – re-explore as soon as possible Integrity of nerve known to be intact – High dose steroids – prednisone at 1mg/kg/day x 10 days and then taper – 72 hours – ENoG to assess degree of degeneration » >90% degeneration – re-explore » 90% expected to regain normal/near normal recovery Complete paralysis following temporal bone fracture – Likely nerve transection – Immediate surgical exploration – 30% need nerve repair Partial or delayed loss of function – Approach similar to iatrogenic partial or delayed loss – High dose steroids – ENoG 72 hours >90% degeneration – explore < 90% degeneration – can monitor and explore at later date depending on worsening or failure to regenerate + General surgical guideline Penetrating Trauma High likelihood of transection – exploration warranted If extratemporal – Do not explore if injury occurs distal to the lateral canthus Nerve endings are very small Rich anastomotic network from other branches in this area – Exploration should occur within 3 days of injury Distal branches can still be stimulated - easier to locate them Delayed exploration with gunshot wounds is recommended – GS results in extensive nerve damage – Waiting a little longer to indentify the extent of injury can be beneficial in forming a surgical plan + Surgery for acute facial nerve trauma Facial nerve decompression: Localise site of injury pre operatively Full exposure of the nerve from IAC to the stylomastoid foramen if can’t localize Approach: Intact - Transmastoid/Middle cranial fossa approach Absent – Transmastoid/Translabyrinthine approach Diamond burs and copious irrigation is utilized to prevent thermal injury Thin layer of bone overlying the nerve is bluntly removed Remove bone fragments and hematoma neurolysis or not to open the nerve sheath is debatable – Recommended to drain hematoma if identified + Neurolysis is debatable Facial nerve neurolysis: Cut epineural sheath few mm on either side of injurypoint Using sharp sickle knife,disposable keratotomy blade or sharp size 11 scalpel blade Should extend to until normal nerve + Acute vs. Late Decompression - Controversial Quaranta et al (2001) examined results of 9 patients undergoing late nerve decompression (27-90 days post injury) who all had >90% degeneration – 7 patients achieved HB grade 1-2 after 1 year – 2 achieved HB grade 3 – Concluded that patients may still have a benefit of decompression up to 3 months out Shapira et all (2006) performed a retrospective review looking at 33 patients who underwent nerve decompression. They found no significant difference in overall results between those undergoing early (30 days post- injury) decompression Most studies like these have been very small, and lack control groups. + Facial Nerve Repair Recovery of function begins around 4-6 months and can last up to 2 years following repair Nerve regrowth occurs at 1mm/day Goal is tension free and healthy anastomosis 2 weeks following injury -> collagen and scar tissue replace axons and myelin – Nerve endings must be excised prior to anastomosis Rule is to repair earlier than later - controversial – After 12-18 months, muscle reinnervation becomes less efficient even with good neural anastomosis – Some authors have reported improvement with repairs as far out as 18-36 months – May and Bienstock recommend repair within 30 days, but other authors have found superior results if done up to 12 months out  + Primary Anastomosis Best overall results of any surgical intervention Done if defect is less than < 2cm – Mobilization of the nerve can give nearly 2cm of length – With more mobilization comes devascularization Endoneurial segments must match - promotes regeneration Ends should be sutured together using three to four 9-0 or 10-0 monofilament sutures to bring the epineurium or perineurium together + Grafting and Nerve Transfer Performed for defects > 2cm Approach is based on availability of proximal nerve ending Success of a nerve graft depends on the following factors: The number of axons remaining in the nerve The potential for regeneration of axons The status of the facial muscles Results in partial or complete loss of donor nerve + Proximal and Distal Segments Great auricular nerve Available – Commonly used, usually in surgical field – Located within an incision made from the mastoid tip to the angle of the mandible – Can only harvest 7-10cm of this nerve – Loss of sensation to lower auricle with use Sural nerve – Located 1 cm posterior to the lateral malleolus – Can provide 35cm of length – Very useful in cross facial anastomosis – Loss of sensation to lateral calf and foot Ansa Cervicalis – only utilized if neck dissection has been performed 92-95% of these patients have some return of facial function – 72-75% have good results (HB 3 or above) + Only Distal Segment Available Requires that the patient have an intact distal nerve segment and facial musculature suitable for reinnervation – Determined by EMG and/or muscle biopsy Hypoglossal nerve – Direct hypoglossal-to-facial graft Distal branch of facial nerve is attached to hypoglossal nerve 42-65% of patient’s expected to experience decent symmetry and tone Complications – atrophy of ipsilateral tongue, difficulties with chewing, speaking, and swallowing – Partial hypoglossal-to-facial jump graft Uses a nerve cable graft, usually the sural nerve, to connect the distal end of the facial nerve to a notch in the hypoglossal nerve Much fewer complications, but increased time of recovery + Only Distal Segment Available Facial-to-Facial Graft – Options Single contralateral branch to distal nerve anastomosis Multiple anastomoses from segmental branches to segmental branches – Commonly sural nerve graft used to connect the buccal branch on the contralateral side to the distal nerve stump – Most do not recommend this technique Weakness caused to the contralateral facial nerve Lack of power to control musculature resulting in poor results + Facial-to-Facial Graft + Surgery for chronic facial nerve paralysis facial nerve paralysis > 1 year Facialmuscles undergo atrophy and scarring lose their ability to contract properly. Reinnervation techniques not suitable Dynamic and static reanimation surgery + Dynamic surgery for facial nerve paralysis Regional muscle transfer: Muscle in the head and neck area rotated into the face along a smiling vector. The native blood and nerve supply to the muscle is maintained so that to create the smile effect, the patient must voluntarily initiate a contraction of the transferred muscle. Currently, the most popular muscle for regional transfer for facial reanimation is the temporalis muscle transfer. Masseter may also used + The temporalis using a hemi-coronal skin incision, temporofascial flap transfer elevated and strip of approximately 2cm TM incised and rotated distally through a preformed subcutaneous tunnel down to the mesiolabial fold. flap connected to the upper lateral part of the orbicularis oris muscle. the act of biting down will result in elevation of the corner of the mouth toward + Dynamic surgery for facial nerve paralysis Microneurovascular free muscle transfer: bring new muscle into the face for reanimation purposes. The gracilis muscle and the latissimus dorsi muscle frequently used Also can use pectoralis minor, serratus anterior, and rectus abdominis Single or two stage surgery 2 stage: nerve grafting done first followed by muscle transplant after 6-12 months + carefully evaluate the patient's for dynamic surgery: Avoid those with remaining potential for spontaneous recovery electromyography (EMG), MST, and Enog are useful + Static reanimation procedures performed to optimize symmetry and reduce complications improve appearance as well as to restore function of the structures of the face Eye: Eyebrow repositioned by unilateral brow lift Eyelid weight Tarsorraphy Nose: nasal valve collapsea: strips of suspension material from the cheekbone, under the skin, to the nasal sidewall, and suspending the nasal sidewall back in its anatomic position. static sling procedures for the corner of the mouth. small cartilage grafts can be inserted into the framework of the nose to widen the cavity slightly. + Static reanimation procedures Corner of mouth: sling techniques: securing a rigid piece of material from the cheekbone, under the skin, down to the corner of the mouth and the upper and lower lip. + THANK YOU