A REVIEW OF CURRENT MANAGEMENT W A V N E C O LIN , D .M .D ., M .D ., M .M E D .S O L ; R. B R U O E DO N O FF, M .D.
ABSTRACT
A fter a year, even the most expert peripheral nerve repair carries a poor prognosis. Early referral and intervention offer the best management of trigem inal nerve injuries.
^ ^ r o m 1983 to 1987, the most common cause of litigious action ; for oral and maxillofacial pro: cedures was p aresthesia.1 ; Altered sensation of the lower : lip and anterior p a rt of the j tongue caused by inferior : alveolar or lingual nerve injury has followed injection injuries,2 : endodontic therapy,3 malposed dental im plants,4 displaced i m andible fracture,5 maxillo facial surgery,6 tum or resection7 ; and often after th ird m olar : removal.8,9 This article reviews the basic biology of peripheral nerve anatom y, injury and regener ation. The clinical evaluation, indications for microsurgical : intervention and current : surgical techniques are also discussed. We em phasize th a t the current standard of care for these complex injuries is early ; referral to clinicians fam iliar with their m anagem ent. NERVE MICROSTRUCTURE
The fundam ental u n it of the peripheral nervous system, including the trigem inal nerve, is the neuron, which has as a major property the conductivity of neural im pulses.10 The 80
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neuron is composed of three parts: the nerve cell body, various dendrites and an axon, which m ay be several feet in length.11 The axon m ay or may not be invested in a myelin sheath delineating two types of nerve fibers, m yelinated and unm yelinated. The myelin sheath consists of m ultiple wrappings of the Schwann cell around a single axon th a t functionally im parts rapid conduction of nerve im pulses.10In contrast, m ultiple unm yelinated axons are frequently enveloped by one Schwann cell. Dem yelination (destruction of the m yelin sheaths by traum atic percus sion),12 prolonged tourniquet application13or a systemic disease such as diabetes14 can produce conduction d isturb ances th a t appear clinically as anesthesia and paresth esia.15 The vascular supply, support, protection and integrity of peripheral nerves are m ain tained by several layers of connective tissue: the endoneurium , perineurium , epineurium and m esoneurium .11 Each nerve fiber is surrounded by an endoneurium , which is composed of a basal lam ina,
collagen m atrix and deficit. A local U N IF A S C IC U L A R endoneurial anesthetic block is an capillaries.16 H undreds example of of thousands of nerve neuropraxia. A nother fibers are in tu rn block, “tourniquet contained w ithin the paralysis,” m ay show next connective tissue no pathologic EPINEURIUM sheath called the perturbations as perineurium . This caused by anoxia or connective tissue focal dem yelinating O L IC O F A S C IC U L A R sheath probably has injury as caused by m ultiple functions compression.23 Since including: protection, axonal continuity is support, sustenance preserved, neural and selective isolation conduction will recover for the underlying in parallel with PERINEURIUM nerve fibers.17 rem yelination in The group of nerve several weeks or fibers surrounded by a m ore.13 P O L Y F A S C IC U L A R perineurium is called a Axonotmetic injuries fascicle.10W ithin a are more severe th an nerve tru n k , there neuropraxic injuries, m ay be one or more less severe th an fascicles arranged into neurotm etric injuries one of three patterns: and are typified by the ENDONEURIUM a m onofascicular crush injury.22 The p a tte rn consisting of a pathosis reveals loss of axonal continuity with single large fascicle, Figure 1- Connective tissue layers and fascicular an oligofasicular a variable degree of patterns of peripheral nerves. p a tte rn of several endoneurial fascicles and a polyfasicular failure of nervous transm ission disruption.24 The axon distal to p a tte rn of m any fascicles or neuronal degeneration th a t the defect is separated from the (Figure l).18 Fascicles mix, would produce sensory d isturb nourishing benefits of the nerve divide and fuse to produce a ances. After resection or tra n cell body and undergoes complex in tra n eu ra l architec section, these layers m ust be progressive breakdown, called W allerian degeneration. tu re .19 Groups of fascicles aligned accurately for the best chance for sensory recovery. compose individual peripheral E ventually proximal axonal nerve sprouts m ay traverse the nerve tru n k s such as the in CLASSIFICATION OF defect and grow into the distal ferior alveolar or lingual nerves NERVE INJURIES nerve trunk, offering a favor and are invested by an epiable prognosis for recovery.25 neurium . The epineurium P eripheral nerve injury has A neurotm etic injury, which protects the underlying nerve classically been divided into three m ajor pathophysiologic is the m ost severe, refers to the fibers by resisting tensile and compressive forces.20 In tu rn , transection of all connective categories: neuropraxia, tissue layers of the peripheral the epineurium is invested in a axonotm esis and neurotm esis.22 nerve tru n k w ith discontinuity These levels of injury m ay be loose areolar connective tissue, of the axon, m yelin sheath, the m esoneurium , which thought of as increasingly endoneurium , perineurium and severe perturbations of the tran sm its the segm ental blood epineurium .22 As before, this supply and allows longitudinal peripheral nerve’s investing defect incites W allerian excursion of the nerve tru n k .21 layers. degeneration. Division of all *■ N europraxia is a focal block We discuss these connective these architectural planes, of neural im pulses with tissue layers because any resulting sensory or motor particularly the endoneurium , derangem ent m ay resu lt in a JADA, Vol. 123, December 1992
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THIRD MOLAR SOCKET
WINDOW INTO MANDIBLE NEUROMA WITH ADHESIONS INTO TOOTH SOCKET PROXIMAL INFERIOR ALVEOLAR NERVE Figure 2. Surgical approach and exposure of the lateral aspect of the mandible for inferior alveolar nerve explorations.
TOOTH SOCKET Figure 3. Surgical approach and exposure of the floor of mouth for lingual nerve explorations.
lessens the chances of neuronal outgrowth and regeneration. A transection injury needs micro82
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neurosurgical intervention for optimal alignm ents of the fascial layers of the nerve
stum ps; otherwise, sensory recovery will be less th an ideal or m ay never occur. Normal sensation consists of touch, tem perature and pain components.26 Each sensory component is conveyed by a different sensory receptor and nerve fiber system .27 Accord ingly, the basic clinical sensory exam ination assesses each sensory receptor and nerve fiber system as represented by each sensory component.28 Some sensory reflex testing m aneuvers are detailed here.29'32 The cutaneous pressure threshold and static two-point discrim ination tests m easure the threshold and innervation density of slowly adapting mechanoreceptors innervated by large-diam eter m yelinated nerve fibers. In contrast, the vibratory threshold and moving two-point discrim ination m easure the threshold and innervation density of the rapidly adapting m echano receptors innervated by small m yelinated or unm yelinated nerve fibers. Pin pressure nocioception assesses small m yelinated and unm yelinated fibers. Diagnostic nerve blocks are helpful in evaluating painful neuropathies to isolate, localize, identify and select those painful neuropathies th a t are candidates for microneurosurgical m anipulation. Abnormal sensations include anesthesia, paresthesia and dysesthesia. A nesthesia is an absence of any sensation or pain, w hereas paresthesia is an abnorm al sensation th a t is not unpleasant33 and m ay be characterized as “pins and needles.” In contrast, dysesthesia is a painful neuropathy either spontaneous
Figure 4. A subtotal transection of the right lingual nerve required an interpositional sural nerve graft.
or evoked w ith or w ithout any background sensation. It in cludes the symptom complexes of hyperalgesia, hyperpathia, sym pathetic m ediated pain and anesthesia dolorosa.34 Hyperalgesia is an evoked pain th a t is rapid and exag gerated in response to non painful stim uli. H yperpathia is a delayed and prolonged pain response. Sym pathetic m ediated pain is worsened by increased sym pathetic tone, emotion and cold. It may be relieved by sym pathetic nerve block. A nesthesia dolorosa is pain in an area of anesthesia.3435
of anesthetic lesions should optimize reinnervation by m inimizing distal nerve trunk atrophy, fibrosis38 and sensory receptor atrophy39 th a t occur w ith time. The optimal tim ing for intervention of these and other injuries, however, is not truly known. Severe nerve paresthesias th a t show no im provem ent at the bim onthly exam should also be explored.37 Fortunately, clinical experience suggests
th a t m ost mild- to-moderate paresthetic lesions resolve spontaneously.8 Dysesthetic injuries, with symptoms of hyperalgesia and hyperpathia, which have been relieved by a peripheral nerve block, will probably respond favorably with surgical m anagem ent.34 After peripheral nerve surgery, the dysesthetic inferior alveolar nerve responds with better pain relief th an the dysesthetic lingual nerve.40 In contrast, sym pathetic m ediated pain, anesthesia dolorosa and central deafferentation pain will not respond as favorably or predictably to surgical m anipulation.34 An observed nerve transec tion, w hether planned or inad vertent, m andates im m ediate microsurgery.6An unplanned nerve transection th a t requires little furth er exposure would be a strong indication for intervention. An im m ediate microreconstruction of a nerve resected during an ablative procedure would also indicate concomitant intervention.
INDICATIONS FOR MICRONEUROSURGERY
The abnorm al sensations of anesthesia, paresthesia or dysesthesia of the inferior alveolar or lingual nerves may be indications for microneurosurgical intervention.3336 Neural lesions th a t produce a per sistent anesthesia for a t least two m onths are consistent with a severe crush injury (axonotmesis) or transection injury (neurotm esis) and justify exploration.37 E arly exploration
Figure 5. A planned resection of the inferior alveolar nerve and mandible for recurrent odontogenic keratocyst. Reconstruction was done with an immediate sural nerve graft and reconstruction plate.
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MICRONEUROSURGICAL TECHNIQUE
At our institution, we explore the inferior alveolar and lingual nerves by extraoral and tra n s oral approaches respectively. The inferior alveolar nerve is approached via a subm an dibular “Risdon” incision with removal of a buccal cortical bony window over the m andib u lar canal (Figure 2). At the same tim e, the lingual nerve is approached via a lingual “neck of tooth” muco-periosteal incision, enabling flap reflection into the floor of the mouth (Figure 3). Originally, the operating microscope was used, but the X4.5 loupes have proven to be more efficient. Typical findings for the inferior alveolar and lingual nerves include extraneural compressive scar bands or foreign objects, nerve collaterals, traum atic neurom as or complete transection (Figure 4).41 The usual techniques include external neurolysis, internal neurolysis, neurorrhaphy or interpositional nerve grafting. Clearly, for a simple nerve transection without tissue loss the preferred repair is direct coaptation of the nerve Dr. Colin is stum ps with instructor, microsutures. Department of Oral Epineurial and Maxillofacial Surgery, The sutures have Massachusetts been the rule General Hospital, and Harvard School to repair the of Dental Medicine. distal Address reprint trigem inal requests to Dr. Colin at Harvard School of branches.33,36-40 Dental Medicine, Since the Department of Oral and Maxillofacial inferior Surgery, 188 alveolar nerve Longwood Ave., is strictly a Boston, 02115. 84
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sensory nerve without a motor component and has a m ultitude of small fascicles,42 individual fascicular suture is not w arranted. W hen neural tissue is resected or has been previously destroyed, a gap forms between the proximal and distal nerve stum ps. Direct approximation of the nerve stum ps would resu lt in harm ful tension across the suture line.43 E ither the nerve should be mobilized, rerouted or a nerve graft interposed to avoid longitudinal su tu re line tension.44 Sacrificing the incisive branch,7or the branch to the lingual mucosa, will frequently allow the re m aining distal inferior alveolar or lingual nerve tru n k to be sufficiently mobilized to allow a tension-free m icroneural anastom osis and obviate the need for a nerve graft. However, a sural or greater auricular nerve graft m ay be indicated to span a large nerve defect (Figure 5).45 OUTCOME WITH MICRONEUROSURGICAL INTERVENTION
U nfortunately, few reports detail the results of micro neurosurgery of the trigem inal nerves. A complete retu rn of sensation in 13 of 18 lingual nerve cases was reported in 1984, but the method of assessing sensory function was not detailed.46 In another study, 18 patients who had undergone nerve surgery were given psychophysical tests sim ilar to those th a t we described earlier. After two years, the author found good touch perception, b u t only fair spatio-temporal responses to painful or therm al stim uli.47 Substantial relief of pain was seen, however, in
patients with hyperalgesia and hyperpathia, but there were poor Dr. Donoff is dean, improvements professor and chief in patients of service, Harvard School of Dental with Medicine. anesthesia dolorosa or sym pathetic m ediated pain.34 In a recent questionnaire, it was deter m ined th a t patients who undergo nerve repair appear m otivated by deficits in oral function and psychosocial issues, both of which were greatly improved by microsurgical intervention as opposed to feeling and pain th a t were only m arginally improved.48 In regard to the tim ing of nerve repair, a subjective report of a “full recovery” of sensory function was m ade when the surgery was w ithin six months of injury. Only 57 percent of seven patients had made a “full recovery” when the operation was done more th an one year after injury.49 W ith the more rigorous sensory reflex testing m easures th a t are used today, fewer patients would likely have been categorized as having m ade a complete recovery. This serves only to reiterate the need for early intervention. SUMMARY
The m anagem ent of trigem inal nerve injuries should no longer be ju st left to nature. Explicit consent stating the known risk of nerve injury before surgical procedures is now a standard of care. Prevention is best practiced by a keen knowledge of anatom y and careful technique. If a sensory disturbance is discovered after
a procedure, a nerve injury should be suspected. Local and systemic support ive care should be instituted to optimize wound healing and minimize discomfort and infection. The patient should be examined, the findings carefully documented and, within the first month, the patient referred for definitive evaluation. For more severe neural insults the extent of anticipated sensory return is time dependent. Beyond one year, even the most expert peripheral nerve repairs carry a poor prognosis. This underscores the need for early referral and intervention by a clinician familiar with the management of trigeminal nerve injuries to offer the best outcome for all involved. ■ 1. St. Paul Insurance Co. (Courtesy of AAOMS). Which OMS procedures present the m ost risk? 1987. 2. H arn SD, D urham TM. Incidence of lingual nerve tra u m a and postinjection complications in conventional m andibular block anesthesia. JADA 1990;121:519-23. 3. Spielm an A, G u tm an D, L aufer D. Anesthesia following endodontic overfilling with AH26. O ral S u rg O ral Med O ral Pathol 1981;52(5):554-6. 4. Shulm an LB, S hepard N J. Complications of dental im plants. O ral Maxillofac Clin N orth Am 1990;2(3):499-513. 5. Bochlogyros PN. A retrospective study of 1,521 m andibular fractures. J Oral Maxillofac Surg 1985;43(8):597-9. 6. K aras ND, Boyd SB, Sinn DP. Recovery of neurosensory function following orthognathic surgery. J O ral Maxillofac Surg 1990;48:124-34. 7. LaBanc JP . Inferior alveolar nerve repair after treatm en t of benign cysts and tum ors of the mandible. O ral Maxillofac Surg Clin North Am 1991;3(l):209-22. 8. Kipp DP, G oldstein BH, Weiss WW. D ysesthesia after m andibular th ird molar surgery: a retrospective study and analysis of 1,377 surgical procedures. JADA 1980;100:185-92. 9. Wofford DT, M iller RI. Prospective study of dysesthesia following odontectomy of im pacted m an d ib u lar th ird m olars. J Oral Maxillofac S urg 1987;45:15-9. 10. Angevine JB . The nervous tissue. In: Bloom W, F aw cett DW, eds. A textbook of histology. P hiladelphia: Saunders; 1975:33385. 11. Sunderland SS. Nerves and nerve injuries. 2nd ed. New York: Churchill Livingstone; 1981. 12. Denny-Brown D, B renner C. The effect of percussion on nerve. J Neurol N eurosurg
Psychol 1944;7:76-95. 13. Fowler T J, D an ta G, G illiatt RW. Recovery of nerve conduction after a pneum atic tourniquet: observations on the hind limb of the baboon. J Neurol N eurosurg Psychiatry 1972;35:638-47. 14. Thomas PK, Eliasson SG. Diabetic neuropathy. In: Dyck P J, Thomas PK, Lam bert EH, Bunge R, eds. Peripheral neuropathy. Philadelphia: Saunders;1984:1773-810. 15. B uchthal F, Rosenfalck A. Sensory potentials in polyneuropathy. B rain 1971;94:241-62. 16. S underland SS. P eripheral nerve trunks. In: S underlund SS, ed. Nerves and nerve injuries. New York: Churchill Livings tone;1981:43-4. 17. Thomas PK, Olsson Y. Microscopic anatom y and function of the connective tissue components of peripheral nerve. In: Dyck P J, Thomas PK, L am bert EH , Bunge R, eds. P eripheral neuropathy. Philadelphia: Saunders;1984:97-120. 18. Millesi H, Terzis JK. Nom enclature in peripheral nerve surgery. Clin P last Surg 1984:11:3-8. 19. Sunderland SS. P eripheral nerve trunks. Funiculi. In: S underland SS, ed. Nerves and nerve injuries. New York: Churchill Livingstone; 1981:31-7. 20. Sunderland SS. P eripheral nerve trunks. The connective tissues of peripheral nerve trunks. In: S underland SS, ed. Nerves and nerve injuries. New York: Churchill Livingstone; 1981:348-40. 21. MacKinnon SE, Dellon AL. Anatomy and physiology of th e peripheral nerve. In: MacKinnon SE, Dellon AL, eds. Surgery of the peripheral nerve. New York: Thieme;1988:4. 22. Seddon HJ. T hree types of nerve injury. Brain 1943:66:247-88. 23. Ochoa J , D anta G, Fowler TJ, G illiatt R. N ature of the nerve lesion caused by pneum atic tourniquet. N ature 1971:233:265. 24. MacKinnon SE, Dellon AL. Classification of nerve injuries as the basis for treatm ent. In: M acKinnon SE, Dellon AL, eds. Surgery of the peripheral nerve. New York: Thieme;1988:35-63. 25. G utm ann E, S anders FK. Recovery of fiber num bers and diam eters in the regeneration of peripheral nerves. J Physiol 1943:101:489-518. 26. Dellon AL. Functional sensation and its re-education. In: Terzis JK , ed. M icroreconstruction of nerve injuries. Philadelphia: S aunders, 1987:181-90. 27. Light AR, Perl ER. Peripheral sensory systems. In: Dyck P J, Thomas PK, Lam bert EH, Bunge R, eds. P eripheral neuropathy. Philadelphia: Saunders;1984:211. 28. Posnick JC , Zim bler AG, Crossm an JAI. Normal cutaneous sensibility of the face. P last Reconstr Surg 1990;86(3):429-33. 29. Ghali GE, E pker BN. Clinical neurosensory testing: practical applications. J Oral Maxillofac S urg 1989;47:1074-8. 30. R ath EM, Essick GK. Perioral somesthetic sensibility: do th e skin of the lower face and the m idface exhibit comparable sensitivity. J O ral Maxillofac Surg 1990;48:1181-90. 31. W aylett-Rendall J. Sensibility evaluation and rehabilitation. Orthop Clin North Am er 1988;19(l):43-56. 32. MacKinnon S, Dellon AL. Diagnosis of nerve injury. In: MacKinnon S, Dellon AL,
eds. Surgery of the peripheral nerve. New York: Thieme; 1988:65-87. 33. LaBanc JP . Trigem inal nerve injuries and repair. Select Readings O ral Maxillofac Surg 1991:l(8):l-20. 34. Gregg JM . Studies of traum atic neuralgia in the maxillofacial region: symptom complexes and response to microsurgery. J O ral Maxillofac Surg 1990:48:135-40. 35. Amadio PC, M ackinnon SE, M erritt WH, Brody GS, Terzis JK . Reflex sym pathetic dystrophy syndrome: consensus report of an ad hoc com mittee of the American Association for H and Surgery on th e definition of reflex sym pathetic dystrophy syndrome. P last Reconstr S urg 1991;87(2):371-5. 36. M eyer RA. Applications of microneuro surgery to the repair of trigem inal nerve injuries. O ral Maxillofac S urg Clin N orth Am 1992; 4:405-16. 37. DonofTRB, ed. M assachusetts General Hospital m anual of oral and maxillofacial surgery. St. Louis: Mosby; 1987:16-8. 38. Holmes W, Young JZ. Nerve regeneration after im m ediate and delayed suture. J A nat 1944;77:63. 39. Terzis JK , Sm ith KL. P eripheral nerve injury-end organ denervation changes. In: Terzis JK , Sm ith KL, ed. The peripheral nerve: structure, function, reconstruction. New York: Raven; 1990:46-9. 40. Donoff RB, Colin W. Neurologic complications of oral an d maxillofacial surgery. O ral Maxillofac Clin N orth Am 1990;2(3):453-62. 41. Gregg JM . Studies of traum atic neuralgias in the maxillofacial region: surgical pathology and neural mechanisms. J Oral Maxillofac Surg 1990;48:228-37. 42. Svane T J, Wolford LM, Milam SB, Bass RK. Fascicular characteristic of the hum an inferior alveolar nerve. J O ral Maxillofac Surg 1986;44:431-4. 43. Miyamoto Y. End-to-end coaptation under tension on repair of peripheral nerves. In: Gorio A, Millesi H, Mingrino S, eds. Posttraum atic peripheral nerve regeneration. New York: Raven; 1981:281-6. 44. S underland SS. T he restoration of nerve tru n k continuity by end-to-end suture. The closure of gaps in peripheral nerves. In: Sunderland S, ed. N erves and nerve injuries. New York: Churchill Livingstone; 1981:555-9. 45. W essberg GA, Wolford LM, E pker BN. Experiences w ith microsurgical reconstruction of the inferior alveolar nerve. J Oral Maxillofac Surg 1982;40:651-5. 46. Mozsary PG, M iddleton RA. Microsurgical reconstruction of the lingual nerve. J O ral Maxillofac S urg 1984;42:415-20. 47. Zuniga JR. M ultim odal scaling of sensory recovery after m icrosurgical repair. J Oral Maxillofac S urg 1990;48(8, Supplem ent l):85-6. 48. Zuniga JR. Perceived expectation, outcome, and satisfaction of microsurgical nerve repair. J Oral Maxillofac Surg 1991;49(8, S upplem ent l):77-8. 49. M ozsary PG, Syers CS. Microsurgical correction of the injured inferior alveolar nerve. J Oral Maxillofac S urg 1985; 43:353-8.
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ABSTRACT
A fter a year, even the most expert peripheral nerve repair carries a poor prognosis. Early referral and intervention offer the best management of trigem inal nerve injuries.
^ ^ r o m 1983 to 1987, the most common cause of litigious action ; for oral and maxillofacial pro: cedures was p aresthesia.1 ; Altered sensation of the lower : lip and anterior p a rt of the j tongue caused by inferior : alveolar or lingual nerve injury has followed injection injuries,2 : endodontic therapy,3 malposed dental im plants,4 displaced i m andible fracture,5 maxillo facial surgery,6 tum or resection7 ; and often after th ird m olar : removal.8,9 This article reviews the basic biology of peripheral nerve anatom y, injury and regener ation. The clinical evaluation, indications for microsurgical : intervention and current : surgical techniques are also discussed. We em phasize th a t the current standard of care for these complex injuries is early ; referral to clinicians fam iliar with their m anagem ent. NERVE MICROSTRUCTURE
The fundam ental u n it of the peripheral nervous system, including the trigem inal nerve, is the neuron, which has as a major property the conductivity of neural im pulses.10 The 80
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neuron is composed of three parts: the nerve cell body, various dendrites and an axon, which m ay be several feet in length.11 The axon m ay or may not be invested in a myelin sheath delineating two types of nerve fibers, m yelinated and unm yelinated. The myelin sheath consists of m ultiple wrappings of the Schwann cell around a single axon th a t functionally im parts rapid conduction of nerve im pulses.10In contrast, m ultiple unm yelinated axons are frequently enveloped by one Schwann cell. Dem yelination (destruction of the m yelin sheaths by traum atic percus sion),12 prolonged tourniquet application13or a systemic disease such as diabetes14 can produce conduction d isturb ances th a t appear clinically as anesthesia and paresth esia.15 The vascular supply, support, protection and integrity of peripheral nerves are m ain tained by several layers of connective tissue: the endoneurium , perineurium , epineurium and m esoneurium .11 Each nerve fiber is surrounded by an endoneurium , which is composed of a basal lam ina,
collagen m atrix and deficit. A local U N IF A S C IC U L A R endoneurial anesthetic block is an capillaries.16 H undreds example of of thousands of nerve neuropraxia. A nother fibers are in tu rn block, “tourniquet contained w ithin the paralysis,” m ay show next connective tissue no pathologic EPINEURIUM sheath called the perturbations as perineurium . This caused by anoxia or connective tissue focal dem yelinating O L IC O F A S C IC U L A R sheath probably has injury as caused by m ultiple functions compression.23 Since including: protection, axonal continuity is support, sustenance preserved, neural and selective isolation conduction will recover for the underlying in parallel with PERINEURIUM nerve fibers.17 rem yelination in The group of nerve several weeks or fibers surrounded by a m ore.13 P O L Y F A S C IC U L A R perineurium is called a Axonotmetic injuries fascicle.10W ithin a are more severe th an nerve tru n k , there neuropraxic injuries, m ay be one or more less severe th an fascicles arranged into neurotm etric injuries one of three patterns: and are typified by the ENDONEURIUM a m onofascicular crush injury.22 The p a tte rn consisting of a pathosis reveals loss of axonal continuity with single large fascicle, Figure 1- Connective tissue layers and fascicular an oligofasicular a variable degree of patterns of peripheral nerves. p a tte rn of several endoneurial fascicles and a polyfasicular failure of nervous transm ission disruption.24 The axon distal to p a tte rn of m any fascicles or neuronal degeneration th a t the defect is separated from the (Figure l).18 Fascicles mix, would produce sensory d isturb nourishing benefits of the nerve divide and fuse to produce a ances. After resection or tra n cell body and undergoes complex in tra n eu ra l architec section, these layers m ust be progressive breakdown, called W allerian degeneration. tu re .19 Groups of fascicles aligned accurately for the best chance for sensory recovery. compose individual peripheral E ventually proximal axonal nerve sprouts m ay traverse the nerve tru n k s such as the in CLASSIFICATION OF defect and grow into the distal ferior alveolar or lingual nerves NERVE INJURIES nerve trunk, offering a favor and are invested by an epiable prognosis for recovery.25 neurium . The epineurium P eripheral nerve injury has A neurotm etic injury, which protects the underlying nerve classically been divided into three m ajor pathophysiologic is the m ost severe, refers to the fibers by resisting tensile and compressive forces.20 In tu rn , transection of all connective categories: neuropraxia, tissue layers of the peripheral the epineurium is invested in a axonotm esis and neurotm esis.22 nerve tru n k w ith discontinuity These levels of injury m ay be loose areolar connective tissue, of the axon, m yelin sheath, the m esoneurium , which thought of as increasingly endoneurium , perineurium and severe perturbations of the tran sm its the segm ental blood epineurium .22 As before, this supply and allows longitudinal peripheral nerve’s investing defect incites W allerian excursion of the nerve tru n k .21 layers. degeneration. Division of all *■ N europraxia is a focal block We discuss these connective these architectural planes, of neural im pulses with tissue layers because any resulting sensory or motor particularly the endoneurium , derangem ent m ay resu lt in a JADA, Vol. 123, December 1992
81
THIRD MOLAR SOCKET
WINDOW INTO MANDIBLE NEUROMA WITH ADHESIONS INTO TOOTH SOCKET PROXIMAL INFERIOR ALVEOLAR NERVE Figure 2. Surgical approach and exposure of the lateral aspect of the mandible for inferior alveolar nerve explorations.
TOOTH SOCKET Figure 3. Surgical approach and exposure of the floor of mouth for lingual nerve explorations.
lessens the chances of neuronal outgrowth and regeneration. A transection injury needs micro82
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neurosurgical intervention for optimal alignm ents of the fascial layers of the nerve
stum ps; otherwise, sensory recovery will be less th an ideal or m ay never occur. Normal sensation consists of touch, tem perature and pain components.26 Each sensory component is conveyed by a different sensory receptor and nerve fiber system .27 Accord ingly, the basic clinical sensory exam ination assesses each sensory receptor and nerve fiber system as represented by each sensory component.28 Some sensory reflex testing m aneuvers are detailed here.29'32 The cutaneous pressure threshold and static two-point discrim ination tests m easure the threshold and innervation density of slowly adapting mechanoreceptors innervated by large-diam eter m yelinated nerve fibers. In contrast, the vibratory threshold and moving two-point discrim ination m easure the threshold and innervation density of the rapidly adapting m echano receptors innervated by small m yelinated or unm yelinated nerve fibers. Pin pressure nocioception assesses small m yelinated and unm yelinated fibers. Diagnostic nerve blocks are helpful in evaluating painful neuropathies to isolate, localize, identify and select those painful neuropathies th a t are candidates for microneurosurgical m anipulation. Abnormal sensations include anesthesia, paresthesia and dysesthesia. A nesthesia is an absence of any sensation or pain, w hereas paresthesia is an abnorm al sensation th a t is not unpleasant33 and m ay be characterized as “pins and needles.” In contrast, dysesthesia is a painful neuropathy either spontaneous
Figure 4. A subtotal transection of the right lingual nerve required an interpositional sural nerve graft.
or evoked w ith or w ithout any background sensation. It in cludes the symptom complexes of hyperalgesia, hyperpathia, sym pathetic m ediated pain and anesthesia dolorosa.34 Hyperalgesia is an evoked pain th a t is rapid and exag gerated in response to non painful stim uli. H yperpathia is a delayed and prolonged pain response. Sym pathetic m ediated pain is worsened by increased sym pathetic tone, emotion and cold. It may be relieved by sym pathetic nerve block. A nesthesia dolorosa is pain in an area of anesthesia.3435
of anesthetic lesions should optimize reinnervation by m inimizing distal nerve trunk atrophy, fibrosis38 and sensory receptor atrophy39 th a t occur w ith time. The optimal tim ing for intervention of these and other injuries, however, is not truly known. Severe nerve paresthesias th a t show no im provem ent at the bim onthly exam should also be explored.37 Fortunately, clinical experience suggests
th a t m ost mild- to-moderate paresthetic lesions resolve spontaneously.8 Dysesthetic injuries, with symptoms of hyperalgesia and hyperpathia, which have been relieved by a peripheral nerve block, will probably respond favorably with surgical m anagem ent.34 After peripheral nerve surgery, the dysesthetic inferior alveolar nerve responds with better pain relief th an the dysesthetic lingual nerve.40 In contrast, sym pathetic m ediated pain, anesthesia dolorosa and central deafferentation pain will not respond as favorably or predictably to surgical m anipulation.34 An observed nerve transec tion, w hether planned or inad vertent, m andates im m ediate microsurgery.6An unplanned nerve transection th a t requires little furth er exposure would be a strong indication for intervention. An im m ediate microreconstruction of a nerve resected during an ablative procedure would also indicate concomitant intervention.
INDICATIONS FOR MICRONEUROSURGERY
The abnorm al sensations of anesthesia, paresthesia or dysesthesia of the inferior alveolar or lingual nerves may be indications for microneurosurgical intervention.3336 Neural lesions th a t produce a per sistent anesthesia for a t least two m onths are consistent with a severe crush injury (axonotmesis) or transection injury (neurotm esis) and justify exploration.37 E arly exploration
Figure 5. A planned resection of the inferior alveolar nerve and mandible for recurrent odontogenic keratocyst. Reconstruction was done with an immediate sural nerve graft and reconstruction plate.
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MICRONEUROSURGICAL TECHNIQUE
At our institution, we explore the inferior alveolar and lingual nerves by extraoral and tra n s oral approaches respectively. The inferior alveolar nerve is approached via a subm an dibular “Risdon” incision with removal of a buccal cortical bony window over the m andib u lar canal (Figure 2). At the same tim e, the lingual nerve is approached via a lingual “neck of tooth” muco-periosteal incision, enabling flap reflection into the floor of the mouth (Figure 3). Originally, the operating microscope was used, but the X4.5 loupes have proven to be more efficient. Typical findings for the inferior alveolar and lingual nerves include extraneural compressive scar bands or foreign objects, nerve collaterals, traum atic neurom as or complete transection (Figure 4).41 The usual techniques include external neurolysis, internal neurolysis, neurorrhaphy or interpositional nerve grafting. Clearly, for a simple nerve transection without tissue loss the preferred repair is direct coaptation of the nerve Dr. Colin is stum ps with instructor, microsutures. Department of Oral Epineurial and Maxillofacial Surgery, The sutures have Massachusetts been the rule General Hospital, and Harvard School to repair the of Dental Medicine. distal Address reprint trigem inal requests to Dr. Colin at Harvard School of branches.33,36-40 Dental Medicine, Since the Department of Oral and Maxillofacial inferior Surgery, 188 alveolar nerve Longwood Ave., is strictly a Boston, 02115. 84
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sensory nerve without a motor component and has a m ultitude of small fascicles,42 individual fascicular suture is not w arranted. W hen neural tissue is resected or has been previously destroyed, a gap forms between the proximal and distal nerve stum ps. Direct approximation of the nerve stum ps would resu lt in harm ful tension across the suture line.43 E ither the nerve should be mobilized, rerouted or a nerve graft interposed to avoid longitudinal su tu re line tension.44 Sacrificing the incisive branch,7or the branch to the lingual mucosa, will frequently allow the re m aining distal inferior alveolar or lingual nerve tru n k to be sufficiently mobilized to allow a tension-free m icroneural anastom osis and obviate the need for a nerve graft. However, a sural or greater auricular nerve graft m ay be indicated to span a large nerve defect (Figure 5).45 OUTCOME WITH MICRONEUROSURGICAL INTERVENTION
U nfortunately, few reports detail the results of micro neurosurgery of the trigem inal nerves. A complete retu rn of sensation in 13 of 18 lingual nerve cases was reported in 1984, but the method of assessing sensory function was not detailed.46 In another study, 18 patients who had undergone nerve surgery were given psychophysical tests sim ilar to those th a t we described earlier. After two years, the author found good touch perception, b u t only fair spatio-temporal responses to painful or therm al stim uli.47 Substantial relief of pain was seen, however, in
patients with hyperalgesia and hyperpathia, but there were poor Dr. Donoff is dean, improvements professor and chief in patients of service, Harvard School of Dental with Medicine. anesthesia dolorosa or sym pathetic m ediated pain.34 In a recent questionnaire, it was deter m ined th a t patients who undergo nerve repair appear m otivated by deficits in oral function and psychosocial issues, both of which were greatly improved by microsurgical intervention as opposed to feeling and pain th a t were only m arginally improved.48 In regard to the tim ing of nerve repair, a subjective report of a “full recovery” of sensory function was m ade when the surgery was w ithin six months of injury. Only 57 percent of seven patients had made a “full recovery” when the operation was done more th an one year after injury.49 W ith the more rigorous sensory reflex testing m easures th a t are used today, fewer patients would likely have been categorized as having m ade a complete recovery. This serves only to reiterate the need for early intervention. SUMMARY
The m anagem ent of trigem inal nerve injuries should no longer be ju st left to nature. Explicit consent stating the known risk of nerve injury before surgical procedures is now a standard of care. Prevention is best practiced by a keen knowledge of anatom y and careful technique. If a sensory disturbance is discovered after
a procedure, a nerve injury should be suspected. Local and systemic support ive care should be instituted to optimize wound healing and minimize discomfort and infection. The patient should be examined, the findings carefully documented and, within the first month, the patient referred for definitive evaluation. For more severe neural insults the extent of anticipated sensory return is time dependent. Beyond one year, even the most expert peripheral nerve repairs carry a poor prognosis. This underscores the need for early referral and intervention by a clinician familiar with the management of trigeminal nerve injuries to offer the best outcome for all involved. ■ 1. St. Paul Insurance Co. (Courtesy of AAOMS). Which OMS procedures present the m ost risk? 1987. 2. H arn SD, D urham TM. Incidence of lingual nerve tra u m a and postinjection complications in conventional m andibular block anesthesia. JADA 1990;121:519-23. 3. Spielm an A, G u tm an D, L aufer D. Anesthesia following endodontic overfilling with AH26. O ral S u rg O ral Med O ral Pathol 1981;52(5):554-6. 4. Shulm an LB, S hepard N J. Complications of dental im plants. O ral Maxillofac Clin N orth Am 1990;2(3):499-513. 5. Bochlogyros PN. A retrospective study of 1,521 m andibular fractures. J Oral Maxillofac Surg 1985;43(8):597-9. 6. K aras ND, Boyd SB, Sinn DP. Recovery of neurosensory function following orthognathic surgery. J O ral Maxillofac Surg 1990;48:124-34. 7. LaBanc JP . Inferior alveolar nerve repair after treatm en t of benign cysts and tum ors of the mandible. O ral Maxillofac Surg Clin North Am 1991;3(l):209-22. 8. Kipp DP, G oldstein BH, Weiss WW. D ysesthesia after m andibular th ird molar surgery: a retrospective study and analysis of 1,377 surgical procedures. JADA 1980;100:185-92. 9. Wofford DT, M iller RI. Prospective study of dysesthesia following odontectomy of im pacted m an d ib u lar th ird m olars. J Oral Maxillofac S urg 1987;45:15-9. 10. Angevine JB . The nervous tissue. In: Bloom W, F aw cett DW, eds. A textbook of histology. P hiladelphia: Saunders; 1975:33385. 11. Sunderland SS. Nerves and nerve injuries. 2nd ed. New York: Churchill Livingstone; 1981. 12. Denny-Brown D, B renner C. The effect of percussion on nerve. J Neurol N eurosurg
Psychol 1944;7:76-95. 13. Fowler T J, D an ta G, G illiatt RW. Recovery of nerve conduction after a pneum atic tourniquet: observations on the hind limb of the baboon. J Neurol N eurosurg Psychiatry 1972;35:638-47. 14. Thomas PK, Eliasson SG. Diabetic neuropathy. In: Dyck P J, Thomas PK, Lam bert EH, Bunge R, eds. Peripheral neuropathy. Philadelphia: Saunders;1984:1773-810. 15. B uchthal F, Rosenfalck A. Sensory potentials in polyneuropathy. B rain 1971;94:241-62. 16. S underland SS. P eripheral nerve trunks. In: S underlund SS, ed. Nerves and nerve injuries. New York: Churchill Livings tone;1981:43-4. 17. Thomas PK, Olsson Y. Microscopic anatom y and function of the connective tissue components of peripheral nerve. In: Dyck P J, Thomas PK, L am bert EH , Bunge R, eds. P eripheral neuropathy. Philadelphia: Saunders;1984:97-120. 18. Millesi H, Terzis JK. Nom enclature in peripheral nerve surgery. Clin P last Surg 1984:11:3-8. 19. Sunderland SS. P eripheral nerve trunks. Funiculi. In: S underland SS, ed. Nerves and nerve injuries. New York: Churchill Livingstone; 1981:31-7. 20. Sunderland SS. P eripheral nerve trunks. The connective tissues of peripheral nerve trunks. In: S underland SS, ed. Nerves and nerve injuries. New York: Churchill Livingstone; 1981:348-40. 21. MacKinnon SE, Dellon AL. Anatomy and physiology of th e peripheral nerve. In: MacKinnon SE, Dellon AL, eds. Surgery of the peripheral nerve. New York: Thieme;1988:4. 22. Seddon HJ. T hree types of nerve injury. Brain 1943:66:247-88. 23. Ochoa J , D anta G, Fowler TJ, G illiatt R. N ature of the nerve lesion caused by pneum atic tourniquet. N ature 1971:233:265. 24. MacKinnon SE, Dellon AL. Classification of nerve injuries as the basis for treatm ent. In: M acKinnon SE, Dellon AL, eds. Surgery of the peripheral nerve. New York: Thieme;1988:35-63. 25. G utm ann E, S anders FK. Recovery of fiber num bers and diam eters in the regeneration of peripheral nerves. J Physiol 1943:101:489-518. 26. Dellon AL. Functional sensation and its re-education. In: Terzis JK , ed. M icroreconstruction of nerve injuries. Philadelphia: S aunders, 1987:181-90. 27. Light AR, Perl ER. Peripheral sensory systems. In: Dyck P J, Thomas PK, Lam bert EH, Bunge R, eds. P eripheral neuropathy. Philadelphia: Saunders;1984:211. 28. Posnick JC , Zim bler AG, Crossm an JAI. Normal cutaneous sensibility of the face. P last Reconstr Surg 1990;86(3):429-33. 29. Ghali GE, E pker BN. Clinical neurosensory testing: practical applications. J Oral Maxillofac S urg 1989;47:1074-8. 30. R ath EM, Essick GK. Perioral somesthetic sensibility: do th e skin of the lower face and the m idface exhibit comparable sensitivity. J O ral Maxillofac Surg 1990;48:1181-90. 31. W aylett-Rendall J. Sensibility evaluation and rehabilitation. Orthop Clin North Am er 1988;19(l):43-56. 32. MacKinnon S, Dellon AL. Diagnosis of nerve injury. In: MacKinnon S, Dellon AL,
eds. Surgery of the peripheral nerve. New York: Thieme; 1988:65-87. 33. LaBanc JP . Trigem inal nerve injuries and repair. Select Readings O ral Maxillofac Surg 1991:l(8):l-20. 34. Gregg JM . Studies of traum atic neuralgia in the maxillofacial region: symptom complexes and response to microsurgery. J O ral Maxillofac Surg 1990:48:135-40. 35. Amadio PC, M ackinnon SE, M erritt WH, Brody GS, Terzis JK . Reflex sym pathetic dystrophy syndrome: consensus report of an ad hoc com mittee of the American Association for H and Surgery on th e definition of reflex sym pathetic dystrophy syndrome. P last Reconstr S urg 1991;87(2):371-5. 36. M eyer RA. Applications of microneuro surgery to the repair of trigem inal nerve injuries. O ral Maxillofac S urg Clin N orth Am 1992; 4:405-16. 37. DonofTRB, ed. M assachusetts General Hospital m anual of oral and maxillofacial surgery. St. Louis: Mosby; 1987:16-8. 38. Holmes W, Young JZ. Nerve regeneration after im m ediate and delayed suture. J A nat 1944;77:63. 39. Terzis JK , Sm ith KL. P eripheral nerve injury-end organ denervation changes. In: Terzis JK , Sm ith KL, ed. The peripheral nerve: structure, function, reconstruction. New York: Raven; 1990:46-9. 40. Donoff RB, Colin W. Neurologic complications of oral an d maxillofacial surgery. O ral Maxillofac Clin N orth Am 1990;2(3):453-62. 41. Gregg JM . Studies of traum atic neuralgias in the maxillofacial region: surgical pathology and neural mechanisms. J Oral Maxillofac Surg 1990;48:228-37. 42. Svane T J, Wolford LM, Milam SB, Bass RK. Fascicular characteristic of the hum an inferior alveolar nerve. J O ral Maxillofac Surg 1986;44:431-4. 43. Miyamoto Y. End-to-end coaptation under tension on repair of peripheral nerves. In: Gorio A, Millesi H, Mingrino S, eds. Posttraum atic peripheral nerve regeneration. New York: Raven; 1981:281-6. 44. S underland SS. T he restoration of nerve tru n k continuity by end-to-end suture. The closure of gaps in peripheral nerves. In: Sunderland S, ed. N erves and nerve injuries. New York: Churchill Livingstone; 1981:555-9. 45. W essberg GA, Wolford LM, E pker BN. Experiences w ith microsurgical reconstruction of the inferior alveolar nerve. J Oral Maxillofac Surg 1982;40:651-5. 46. Mozsary PG, M iddleton RA. Microsurgical reconstruction of the lingual nerve. J O ral Maxillofac S urg 1984;42:415-20. 47. Zuniga JR. M ultim odal scaling of sensory recovery after m icrosurgical repair. J Oral Maxillofac S urg 1990;48(8, Supplem ent l):85-6. 48. Zuniga JR. Perceived expectation, outcome, and satisfaction of microsurgical nerve repair. J Oral Maxillofac Surg 1991;49(8, S upplem ent l):77-8. 49. M ozsary PG, Syers CS. Microsurgical correction of the injured inferior alveolar nerve. J Oral Maxillofac S urg 1985; 43:353-8.
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