Anatomical Study of the Feasibility of Contralateral Mental Nerve Coaptation with Magnetoencephalography of patients with Unilateral Innervation of the Mental Nerve Dermatome
post-operative anesthesia of the lower lip. Given the length of
resection necessary for most segmental mandible tumor exonerations,
the IAN is unable to sprout and span the segmental gap. There are
case reports of patients regaining sensation to the lower lip after
segmental mandibulectomy. The anatomical confines of the mental nerve
area make re-innervation via collateral c-fiber sprouting across the
midline from the contralateral IAN highly likely. This raises an
interesting neurological question: on which side of the face will the
patient perceive tactile sensation? A nerve typically gives rise to
sensation on its own side of the face. If re-innervation is from the
contralateral side but the sensation is perceived qualitatively by the
patient on the damaged side, this would suggest for the first time
that one hemisphere of the brain can produce somatosensory qualia that
are perceived to originate from the ipsilateral side of the face, and
that something about the nerve signal dictates the lateralization. In
this study we attempt to test the feasibility of expediting the
reafferentation of the contralateral anesthetized region, both
anatomically and functionally.
Based on the collateral re-innervation across the midline we suggest a
conceptual surgical approach: It may be possible to expedite alveolar
nerve regrowth by grafting the severed mental nerve to the intact
contralateral mental nerve. Relatively recent development and
understanding of nerve tubes offers a new tool to help bridge the
midline neurosensory gap. Anatomical studies have been conducted with
nine cadavers; of interest in particular was the feasibility of
reflecting the non-affected side's m-branch of the mental nerve for
contralateral reinnervation without the use of a nerve graft. Sham
surgeries using nerve regrowth conduits and reflected cross-facial
mental nerve reflection have also performed, and have shown this
approach to be entirely feasible in some patients.
In order to assess perceptual and cortical representation of tactile
stimuli to the anesthetized region in patients with
hemimandibulectomy, subjects were clinically evaluated for sensory
functioning on their chin: on the midline and both contralaterally and
ipsilaterally from the region of nerve ablation. Examination focussed
on techniques that delineate what type of nerve fibers have
regenerated (C,β,α-Fibers).
Finally, we submitted one hemimandibulectomy patient to functional
imaging using Magnetoencephalography (MEG), an imaging modality which
allows for millisecond-level temporal resolution and high sensitivity
recordings of the magnetic fields created by the simultaneous firing
of many neurons in the cerebral cortex. This allowed for the
identification of the anatomical brain locations active during tactile
stimulation of the skin. We found that both ipsilateral and
contralateral activation was present in near-midline touch of both
affected and unaffected sides.
The results of these experiments show both the surgical feasibility of
a graftin of the severed mental nerve to the intact contralateral
mental nerve, and the likelihood that patients will regain function
and perhaps, with training, correct perception for this
reafferentation.
All experiments involving human subjects have been conducted under the
auspices of the UCSD IRB, under UCSD IRB Protocol #081673. Subjects
consented to undergoing examination for nerve function as well as
non-invasive imaging, magnetoencephalography (MEG).
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2. Kaban LB, Upton J. Cross mental nerve graft for restoration of lip sensation
after inferior alveolar nerve damage: report of case. J Oral Maxillofac Surg.
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