CC
An 18-year-old female is referred to a microneurosurgeon for evaluation of numbness of her left tongue.
HPI
The patient had all four third molars surgically removed by an oral and maxillofacial surgeon 13 weeks before presentation. Upon follow-up at 7 days with the referring surgeon, the patient complained of persistent loss of feeling in her left tongue and altered taste sensation. No neurosensory testing was done at that time. Six weeks after surgery, the patient continued to report profound numbness of the left tongue and no improvement in taste perception. All surgical wounds were healed. Neurosensory testing (NST) of the tongue (pinprick and light touch) demonstrated total anesthesia (absence of perception of any stimulation of the mucosa) of the anterior two-thirds of the left tongue, floor of the mouth, and lingual gingiva. Photographic documentation of the affected area of the tongue was obtained. An appointment was made for reevaluation of the patient in 4 weeks. At follow-up (10 weeks postsurgery), repeat NST revealed no change (persistent total anesthesia) from the previous examination. The patient was subsequently referred to a microneurosurgeon for evaluation of left lingual nerve (LN) injury.
The patient also complained of pain radiating into her left tongue when chewing food or brushing her left lower teeth (allodynia) and frequent accidental biting of her tongue. ( Allodynia is defined as pain caused by a stimulus that does not normally produce pain. Dysesthesia is an unpleasant abnormal sensation, either spontaneous or evoked, and anesthesia dolorosa is pain in an area or a region that is anesthetic.)
PMHX/PDHX/medications/allergies/SH/FH
Noncontributory.
Examination
General . The patient is a well-developed and well-nourished adolescent female in no apparent distress.
Maxillofacial . There is no cervical lymphadenopathy. Maximum interincisal opening is 51 mm without mandibular deviation, and all extraction and surgical sites are healed. There are no oral masses or ulcerations; no fasciculations, deviation, or atrophic changes of the tongue; and no evidence of recent tongue trauma (scars or lacerations). Inspection of the lingual and buccal aspects of the mandible reveals no abnormalities (texture, color, and consistency of mucosa are within normal limits). Palpation and percussion of the lingual surface of the posterior mandible adjacent to the third molar area produced a localized painful sensation that radiated to the left tongue.
Clinical neurosensory . This examination is performed at three levels, A, B, and C ( Box 29.1 ), because it is critical to determine mechanoreceptive and nociceptive sensory deficits or alterations in comparison with the patient’s intact side when working up LN injury. Additionally, it can be useful to check for Tinel’s sign, though this may be a later presenting symptom (positive Tinel’s sign: a provocative test of regenerating nerve sprouts in which light percussion over the nerve elicits a distal tingling sensation; it is often interpreted as a sign of small fiber recovery, but after LN injury with complete severance, this response likely represents proximal stump neuroma formation and phantom pain). Cranial nerves (CNs) II through XII were intact except for the left LN distribution, mandibular division (V3 of the left trigeminal nerve [CN V]). The patient showed no response to any of the three levels of NST, which supports a diagnosis of anesthesia.
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Level A (directional and two-point discrimination): Patient unable to feel the direction of the stimulus applied with a cotton swab and unable to feel a single- vs two-point stimuli applied to the affected side. Control side within normal limits (inability to discriminate two points farther than 6.5 mm apart is considered abnormal).
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Level B (contact detection): Patient does not experience pain upon repetitive application of touch or pressure. Control side is within normal limits.
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Level C (pain sensitivity): Patient shows no response to pinprick, noxious pressures, and heat on the left lingual nerve distribution. Control side is within normal limits.
In patients with abnormal pain sensations (allodynia, anesthesia dolorosa, dysesthesia), a local anesthetic block of the involved nerve may be helpful in making treatment decisions. If the pain is abolished during the duration of the local anesthetic block, there is a reasonable possibility of pain relief from microneurosurgical repair of the injured nerve.
Imaging
Panoramic radiograph (11 weeks postsurgery) reveals no evidence of retained root fragment or foreign bodies. The outline of the socket of the right mandibular third molar is well demarcated and is appropriate for the stage of healing. Assessment of the LN is possible with a magnetic resonance imaging study (preferably magnetic resonance neurography), but this is not generally necessary in making treatment decisions.
Labs
No routine or special laboratory tests are indicated for microneurosurgical evaluation unless dictated by the medical history.
Assessment
Left LN injury, exhibiting complete anesthesia to NST at 13 weeks after injury, is a neurotmesis, or Sunderland fifth-degree injury (i.e., nerve injury with anatomic disruption of all axonal and sheath elements and/or physiologic block of all impulse transmission, producing wallerian degeneration and probable neuroma formation) ( Table 29.1 ).
| Seddon | Sunderland | Histology | Outcomes |
|---|---|---|---|
| Neurapraxia | First degree | No axonal damage, no demyelination, and no neuroma | Rapid recovery (days to weeks) |
| Axonotmesis | Second, third, and fourth degree | Some axonal damage, demyelination, possible neuroma | Loss of sensation; slow, incomplete recovery (weeks to months); microsurgery may help |
| Neurotmesis | Fifth degree | Severe axonal damage, nerve discontinuity, neuroma formation | Loss of sensation; spontaneous recovery unlikely; microsurgery may help |
Surgical intervention is indicated for microrepair of the left LN (i.e., excision of the proximal stump neuroma and, most likely, neurorrhaphy [repair of a severed nerve by suturing the two nerve ends together]) or reconstruction of a nerve gap with a graft to allow for a tension-free repair.
Treatment
The two most important factors in successful decision making regarding treatment of peripheral trigeminal nerve injuries are prompt evaluation of suspected nerve injuries and correct patient selection (diagnosis). There is a time constraint on the interval after injury in which a peripheral nerve can be repaired with reasonable expectation of success, with most literature demonstrating worsening outcomes if repair is not performed within 6 months of nerve injury. After injury, severed axons in the nerve undergo wallerian degeneration over a period of 1 to 2 months. If the distal endoneurial sheaths of the necrotic axons are not recannulated with new axonal sprouts from the proximal nerve stump within a critical interval (probably 9–12 months after injury), the endoneurial sheaths collapse and are replaced with scar tissue, making reinnervation unlikely or impossible. The selection of patients who might benefit from surgical intervention is based on a standardized neurosensory examination. Patients with unacceptable partial or complete loss of sensation, with or without pain symptoms, are most likely to benefit from microsurgical repair of nerve injuries.
Surgical treatment of peripheral nerve injuries follows a stereotypical series of steps, performed in order. These include external decompression, internal neurolysis, preparation of nerve stumps (including excision of scar tissue and neuromas), neurorrhaphy, reconstruction of a nerve gap, and if the nerve is found not to be repairable, other steps ( Table 29.2 ). Specific intraoperative findings dictate the surgical treatment modality.
| Procedural Steps a | Description |
|---|---|
|
Removal of bone, scar tissue, and foreign material (e.g., root canal filling material, missile fragments, internal fixation wires, screws, or plates); exposure of nerve |
|
Incision of epineurium, inspection of internal nerve structure, removal of scar tissue, repair of individual fascicles |
|
Excision of neuroma or scar tissue, exposure of viable nerve tissue in nerve stumps, mobilization of proximal and distal nerve limbs to allow approximation |
|
Approximation and suturing of nerve stumps without tension |
|
Autogenous nerve graft; processed allogeneic nerve graft; alloplastic nerve guide |
|
When proximal nerve is not available, anastomosis of proximal stump of nearby nerve (e.g., great auricular nerve) to viable distal stump of injured nerve using a bridging autogenous nerve graft (e.g., sural nerve) |
|
Nerve capping; nerve redirection; neurectomy (only for pain of terminal malignancy) |
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