Chapter 27: Trigeminal Nerve Injury Flashcards
What are the major classification systems of nerve injury?
- Seddon
2. Sunderland
Describe Seddon classification?
- Neuropraxia: nerve sheath intact, axons intact, no Wallerian degeneration, conduction failure transitory, complete recovery within 4 weeks
- Axonotmesis: nerve sheath intact, some axons can be disrupted, Wallerian degeneration present in some axons, conduction failure is prolonged, partial spontaneous recovery that can take months
- Neurotmesis: nerve sheath interrupted, all axons interrupted, Wallerian degeneration in all axons, conduction failure permanent, poor to none spontaneous recovery, time of recovery none (if not begun by 3 months)
What is neuropraxia?
Seddon classification in which the nerve sheath is intact, the axons are intact and there will be no Wallerian degeneration. The paresthesia is transitory and usually conduction failure is ~4 weeks
What is axonotmesis?
Seddon classification in which the nerve sheath is intact but some axons can be disrupted. Wallerian degeneration can be present in some axons resulting in prolonged paresthesia and only partial spontaneous recovery that can takes months
What is neurotmesis?
Seddon classification in which the nerve sheath is interrupted and as well as all axons. Wallerian degeneration is present in all axons with conduction failure likely permanent. If recovery has not begun by 3 months s/p injury it is unlikely that it will occur.
What is Wallerian degeneration?
Wallerian or anterograde degeneration is a series of molecular and cellular events triggered throughout the distal nerve stump and within a small reactive zone at the tip of the proximal stump. The primary histologic changes involved cytoskeletal fragmentation of both the axons and myelin.
What are the 4 types of neuroma based on gross morphology
- Lateral adhesive
- Lateral exophytic
- Neuroma-in-continuity
- Amputation neuroma
What is dysesthesia?
Unpleasant, abnormal sensation that can be either spontaneous or provoked
What is the difference between analgesia and anesthesia?
Analgesia is the absence of pain in response to stimulation that would normally be painful. Anesthesia is the absence of the perception of stimulation by noxious or non-noxious stimulation of skin or mucosa. Anesthesia can be divided into central, regional or local types
What are the common symptoms of hyperesthesia?
Shooting, flashing, burning pain produced by normally non-painful stimuli
What is hyperpathia?
Characterized by increased reaction to a stimulus and increased threshold for response. It commonly is induced by repetitive mechanical pressures and characterized by faulty identification and localization of stimuli
What is hypoalgesia?
Diminished response to normally painful stimulus
What is paresthesia?
Abnormal sensation, either invoked or spontaneous, that is not necessarily unpleasant or painful (as noted in dysethesia)
What is SMP (sympathetically mediated pain)?
Throbbing, diffuse and hyperalgesic pain perpetuated by abnormal reflex activity in sympathetic pathways following peripheral nerve injury. The classic syndromes of complex regional pain syndrome are theorized to involve both peripheral and central mechanisms.
What are the symptoms of SMP (sympathetically mediated pain)?
Described as burning, hot, lanciting pain. People complain of increased pain intensity during stressful periods.
What is Tinel’s sign?
A provocative test of regenerating nerve sprouts in which light percussion over the nerve elicits a distal tingling sensation. It is used as a sign of small fiber recovery but is poorly correlated with functional recovery and easily confused with neuroma formation.
What is deafferentiation pain?
Pain in a body region of partial or complete traumatic peripheral nerve deficit in which retrograde central neuropathy has occurred. Deafferentation mechanisms have been implicated in phantom pain, hyperpathia and allodynia
How many axons and fascicles are in the IAN?
7000-12000 axons
10-24 fascicles
What is the incidence of IAN and lingual nerve injury during 3rd molar removal?
IAN, lingual, and to a lesser frequency long buccal, ranges between 0.6% and 5.0%. In general, incidence of IAN is higher than lingual (one study, incidence of IAN 1.2% vs 0.9% for lingual).
What is the percentage of spontaneous lingual nerve recovery?
96%
What are risk factors associated with trigeminal nerve injury during extraction?
- Age
- Surgical technique
- Surgeon experience
- Proximity to nerve to tooth
What factors are associated with a higher incidence of lingual nerve injury during the course of third molar removal?
Lingually angulated impaction (typically have eroded or absent lingual cortical plate 2/2 infection or cyst; this exposes the nerve directly to damage during instrumentation to remove the tooth)
What is the average rate of an injured axon’s forward growth?
1-2mm/day
What are the potential clinical manifestations of a trigeminal nerve injury?
- Non-painful anesthesia and hypoesthesia
- Painful anesthesia and hypoesthesia
- Non-painful hyperesthesia
- Painful hyperesthesia
How should open nerve injuries be managed?
It is best managed with primary repair if appropriate. Otherwise, delayed primary (usually within the first few postoperative days) vs delayed secondary repair (>3 weeks) are other options.
When should closed (unobserved) nerve injuries be addressed?
- Intolerable anesthesia of more than 3 months
- Painful symptoms that persist more than 4 months where the painful symptoms are relieved with local infiltration
- Intolerable deterioration of sensation beyond 4 months and no improvement of sensation beyond 4 months
What are the types of nerve repair?
- Epineural
- Perineural
- Group fasicular
Which type of nerve repair is appropriate for IAN?
For mixed motor and sensory: perinerual and group fasicular suturing
For sensory IAN: epineural
What does coaptation refer to in nerve repair?
Bringing individual nerve fascicles into the best possible alignment. Direct neurorraphy can only be performed when nerve is tension free
If a defect is too large for a direct neurorraphy, which nerves may be considered as donors? What lengths are they ideal for?
Sural ( up to 2.5 cm)
Greater auricular (up to 1.5 cm)
Median antebrachial cutaneous
What factors govern the choice of a donor site for free nerve repair?
- Accessibility
- Length required
- Diameter of donor nerve compared with host
- Patient preference
- Fasicular number and pattern
What is the average diameter of the IAN? What is the average diameter of the lingual nerve?
2.4mm; 3.2mm
What is the geometric shape of the IAN? What is the geometric shape of the lingual nerve?
Both are cylindrical (differ from sural- flat, greater auricular- flat)
Which nerve is the best donor site for an interpositional graft for an IAN defect of approximately 25mm
Sural nerve. Can provide up to 30mm of graft harvest.
What does the sural nerve innervate?
Innervates the posterior and lateral aspects of the leg and foot
How doe the axon number and size of a sural nerve compare to IAN?
Sural nerve has 50% fewer axons and smaller axonal size.
Which nerve is the best donor site for an interpositional graft for smaller defects (up to 15mm long) of IAN?
Greater auricular nerve.
How does the axon number and size of the greater auricular nerve compare to the IAN?
Comparable in terms of axonal size and axonal numbers however, the GAN is half the diameter and has half the fascicles.
What is a cable graft?
2 parallel strands (especially for greater auricular to IAN) to achieve better size match
How much nerve should be harvested for a graft?
25% longer than defect, to account for primary contracture
When is delayed nerve repair in the maxillofacial region indicated?
If a wound is grossly contaminated or mechanism of injury may cause scarring of the proximal and distal ends (ex: blunt avulsion injuries 2/2 gunshot or MVC)
How is the term anastamosis applied to nerve injuries?
Trick question. Anastamosis is not appropriate nomenclature when discussing nerve repair. Vessels are anastamosed, nerves are repaired or reconstructed.
What type of suture material is most compatible for nerve repair?
Inert and non-resorbable such as 8-0 or 9-0 monofilament nylon or poly-propylene
What potential alloplastic nerve conduits may be used in nerve reconstruction
- type 1 collagen tubes
- expanded polytetrafluoroethylene
- polyglycolic acid tubes
What method is used for locating the greater auricular nerve?
A line is drawn connecting mastoid process to the angle of the mandible. A perpendicular line is then drawn to bisect the mastoid-mandible line. The greater auricular nerve approximates this second line.
What are generally accepted success rates of IAN hypoesthetic and hyperesthetic nerve repair?
Hypoesthetic: 85%
Hyperesthetic: 55.6%
What are generally accepted success rates of lingual nerve hypoesthetic and hyperesthetic nerve repair?
Hypoesthetic: 87%
Hyperesthetic: 67.5%
What is the most significant factor of functional neurosensory recovery?
Timing of surgical intervention
What are the theories associated with local anesthesia related trigeminal nerve injury? Which one is more likely?
1.intraneural mechanical injury; 2. indirect chemical neurotoxicity.
chemical neurotoxicity: 1.LA injuries involve entire nerve distribution, 2.higher percentage of dysesthesia seen among pts with LA injuries than in cases where injury known to be mechanical, 3. direct nerve contact during injection does not appear to be present in at least 50% of cases.
What are the basic steps in nerve repair?
- Decompression (expose, clean, evaluate)
- Neuroma resection
- Neurorraphy vs graft
What are the various autologous grafts?
- Nerve
- Muscle plugs
- Vessels
