Masseteric Nerve Transfer for Facial Paralysis Secondary to Parotid Malignancy: A Retrospective Case Series.

Background: The objective outcomes of masseteric nerve transfer in the setting of parotid malignancy are unclear. Objective: To measure objective facial reanimation outcomes of masseteric nerve transfer in patients with parotid malignancy who underwent parotidectomy with facial nerve resection. Materials and Methods: Retrospective review of patients who underwent masseteric nerve transfer for facial paralysis secondary to parotid malignancy was carried out at a tertiary referral hospital from August 2017 to November 2021. Objective facial reanimation outcomes were analyzed using Emotrics. Minimal follow-up of 6 months was required for inclusion. Results: Eight patients (five males) with a median age of 75.5 years (range 53-91) met inclusion criteria. Fifty percent had metastatic squamous cell carcinoma, and 50% had primary parotid malignancy. Five patients underwent concomitant cancer resection with facial nerve reconstruction. Seven patients received postoperative adjuvant radiotherapy. After reinnervation, patients had improved oral commissure excursion (from 1.51 mm ±1.27 to 3.77 mm ±1.81; p < 0.01) and facial symmetry during smile. Conclusion: In this study, masseteric nerve transfer enhanced oral commissure excursion and facial symmetry during smile in patients with parotid malignancy and facial nerve resection.

Restoring the spontaneous smile through free functional muscle transfer. A systematic review and meta-analysis of the last twenty years' experience.

BACKGROUND: The recovery of the spontaneous smile has become a primary focus in facial reanimation surgery and its major determinant is the selected neurotizer. We aimed to compare the spontaneity outcomes of the most preferred neurotization methods in free functional muscle transfer for long-standing facial paralysis. METHODS: The Embase, Ovid Medline, and PubMed databases were queried with 21 keywords. All clinical studies from the last 20 years reporting the postoperative spontaneity rate for specified neurotization strategies [cross-face nerve graft (CFNG), contralateral facial nerve (CLFN), motor nerve to the masseter (MNM), and dual innervation (DI)] were included. A meta-analysis of prevalence was performed using Freeman-Tukey double arcsine transformation, I2 statistic, and generic inverse variance with a random-effects model. Risk Of Bias In Non-randomized Studies of Interventions and Newcastle-Ottawa scale were used to assess bias and study quality. RESULTS: The literature search produced 2613 results and 473 unique citations for facial reanimation. Twenty-nine studies including 2046 patients were included in the systematic review. A meta-analysis of eligible data (1952 observations from 23 studies) showed statistically significant differences between the groups (CFNG: 0.94; 95% confidence interval [CI], 0.76-1.00, CLFN: 0.91; 95% CI, 0.49-1.00, MNM: 0.26; 95% CI, 0.05-0.54, DI: 0.98; 95% CI, 0.90-1.00, P < 0.001). In pairwise comparisons, statistically significant differences were found between MNM and other neurotization strategies (P < 0.001 in CFNG compared with MNM, P = 0.013 for CLFN compared with MNM, P < 0.001 for DI compared with MNM). CONCLUSIONS: DI- and CLFN-driven strategies achieved the most promising outcomes, whereas MNM showed the potential to elicit spontaneous smile at a lower extent. Our meta-analysis was limited primarily by incongruency between spontaneity assessment systems. Consensus on a standardized tool would enable more effective comparisons of the outcomes.

Sensory innervation of masseter, temporal and lateral pterygoid muscles in common marmosets.

Myogenous temporomandibular disorders is associated with an increased responsiveness of nerves innervating the masseter (MM), temporal (TM), and lateral pterygoid muscles (LPM). This study aimed to examine sensory nerve types innervating MM, TM and LPM of adult non-human primate-common marmosets. Sensory nerves were localized in specific regions of these muscles. Pgp9.5, marker for all nerves, and NFH, a marker for A-fibers, showed that masticatory muscles were primarily innervated with A-fibers. The proportion of C- to A-fibers was highest in LPM, and lowest in MM. All C-fibers (pgp9.5+/NFH-) observed in masticatory muscles were peptidergic (CGRP+) and lacked mrgprD and CHRNA3, a silent nociceptive marker. TrpV1 was register in 17% of LPM nerves. All fibers in masticatory muscles were labeled with GFAP+, a myelin sheath marker. There were substantially more peptidergic A-fibers (CGRP+/NFH+) in TM and LPM compared to MM. MM, TM and LPM NFH+ fibers contained different percentages of trkC+ and parvalbumin+, but not trkB+ fibers. Tyrosine hydroxylase antibodies, which did not label TG, highlighted sympathetic fibers around blood vessels of the masticatory muscles. Overall, masticatory muscle types of marmosets have similarities and differences in innervation patterns.

Neurectomy of the Masseteric Nerve Using an Extra-Oral Approach to Treat Masseter Hypertrophy: Case Report and Literature Review.

Masticatory muscle hypertrophy is a benign clinical anomaly which leads to facial asymmetry or a squared face appearance. We report a case of masticatory muscle hypertrophy, particularly on the right side, that was successfully treated by neurectomy of the right masseteric nerve through an extra-oral approach. Clinical examination showed significant aesthetic improvement of the facial symmetry with complete paralysis and atrophy of the right masseter muscle. The impaired postoperative function of the frontal branch of the right facial nerve was fully restored 10 weeks postoperatively. The patient no longer experiences headaches or discomfort with eating or sleeping on her right side.

Extra- and intramuscular innervation of the masseter: Implications for facial reanimation.

PURPOSE: Irreversible facial paralysis results in significant functional impairment. The motor nerve to the masseter is a reconstructive option, but despite its clinical importance, there are few parametric anatomic studies of the masseteric nerve. The purpose of this study was to investigate the extra- and intramuscular innervation of the masseter in 3D to determine the relationship of the nerve to the muscle heads and identify landmarks to aid identification. MATERIALS AND METHODS: The nerve was dissected throughout its entire course in eight formalin-embalmed cadaveric specimens (mean age 84.9 ± 12.2 years). The nerve was digitized at 1-2 mm intervals using a MicroScribe™ digitizer and modeled in 3D in Autodesk® Maya®. RESULTS: Two or three extramuscular nerves were found to enter the deep head (DH) of the masseter: one main "primary" nerve (n = 8) and one (n = 4) or two (n = 4) smaller primary nerve(s). The main primary nerve supplied both the deep and superficial heads, whereas the smaller primary nerve(s) only supplied the DH. Surgical landmarks for masseter nerve localization were quantified. CONCLUSIONS: Comprehensive mapping of the innervation of the masseter muscle throughout its volume revealed neural partitioning that could provide a basis for safety planning for muscle flaps and donor nerve identification and explain why masseter functional loss is not incurred by donor nerve sacrifice. Quantified landmarks correlate to previous studies and support the constant anatomy of this nerve. Our results provide a basis to optimize surgical approaches for donor nerve and muscle flap surgery.

Nerve guide conduits, nerve transfers, and local and free muscle transfer in facial nerve palsy.

PURPOSE OF REVIEW: To highlight the recent literature on reinnervation options in the management of facial nerve paralysis using nerve conduits, and nerve and muscle transfers. RECENT FINDINGS: Engineering of natural and synthetic nerve conduits has progressed and many of these products are now available on the market. The use of the masseter nerve has become more popular recently as a choice in nerve transfer procedures due to various unique advantages. Various authors have recently described mimetic muscle reinnervation using more than one nerve transfer, as well as dual and triple innervation of free muscle transfer. SUMMARY: The ideal nerve conduit continues to be elusive, however significant progress has been made with many natural and synthetic materials and designs tested and introduced on the market. Many authors have modified the classic approaches in motor nerve transfer, as well as local and free muscle transfer, and described new ones, that aim to combine their advantages, particularly the simplification to a single stage and use of multiple reinnervation to the mimetic muscles. These advances are valuable to the reconstructive surgeon as powerful tools that can be tailored to the unique challenges of patients with facial nerve palsy looking for dynamic reanimation options.

Comparison of static and dynamic symmetry between masseter-innervated and dual-innervated free multivector serratus anterior muscle transfer for complete facial paralysis.

PURPOSE: In this study, facial symmetry was compared between the masseter-innervated and dual-innervated free multivector serratus anterior muscle transfer (FMSAMT) methods. METHODS: Eighteen patients with unilateral complete facial paralysis underwent facial reanimation surgery between April 2006 and July 2019. The masseter-innervated FMSAMT group (Group M, n = 8) underwent end-to-end coaptation with the ipsilateral masseter nerve in one stage. The dual-innervated FMSAMT group (Group D, n = 10) underwent end-to-end coaptation with the masseter nerve and end-to-side coaptation with the contralateral facial nerve via cross-face nerve graft. They were further divided into the one-stage (Group D1, n = 5) and two-stage (Group D2, n = 5) subgroups. The durations of periods until the first visible muscle contraction with clenching, first spontaneous smile, and the completion of resting tone were evaluated. The possibility of a spontaneous smile and symmetry of the midline and horizontal deviation at rest and during voluntary smiling were compared between each group. RESULTS: Groups M and D differed significantly in the possibility of a spontaneous smile and improvement rate of midline deviation and horizontal deviation at rest (p < 0.001, p < 0.001, and p = 0.001, respectively) but not in the improvement rate of midline and horizontal deviation during voluntary smiling. The duration of the period until the completion of resting tone was significantly shorter in Group D1 than in Group D2 (p = 0.048); however, the possibility of a spontaneous smile and the improvement rate of midline and horizontal deviation were not significantly different. CONCLUSIONS: Dual-innervated FMSAMT was effective in guaranteeing a symmetrical resting tone, voluntary smiling, and reproducing a spontaneous smile.

Outcomes of immediate facial nerve reanimation with nerve transfer for facial nerve neoplasm-induced paralysis: a retrospective review.

BACKGROUND: The purpose of this study was to evaluate the outcomes of our polyneural, zone-based reanimation approach for patients with neoplasm-induced facial paralysis. METHODS: A retrospective review of consecutive patients who underwent facial reanimation surgery using multiple donor nerve transfers was undertaken. In each case, the selection of donor nerves was based on the availability of donor nerve and the viability of the motor endplate on the affected side. Sources of the neural inputs utilized included the remnant facial nerve stump, masseteric nerve, partial hypoglossal nerve, and branches of the contralateral facial nerve. Clinical outcomes were scored by expert raters. Ratings were undertaken using the modified House-Brackmann, eFACE and MEEI FACEgram scoring systems. RESULTS: Between 2017 and 2020, 12 patients were included in the study (mean age 60 years; range 26-81 years). Eight patients (67%) achieved a grade III outcome on the modified House-Brackmann grading scale. Mean eFACE static and dynamic scores were 76 and 57 respectively, reflecting a high degree of symmetry at rest and moderate restoration of dynamic movement. Mean time to movement was 5.4 months (SD 1.9). Objective FACE-gram measurements confirmed restoration of midface movement with an average improvement in smile excursion and mouth angle excursion of 3.19 mm (SD 3.18) and 4.81° (SD 2.90) respectively. CONCLUSION: Facial reanimation using multiple nerve transfers is effective in achieving improvements in facial function and symmetry.

Surgical Anatomy for Asian facial Contouring: A Personal Perspective.

This paper introduces my personal perspective on anatomic structures for reduction malarplasty, mandibular contouring surgery, and masseter muscle resection. The zygomaticofacial nerve innervates a rectangular area, and each side measures 18.8±4 and 15.8±3.4 mm. The center of the rectangle is located laterally, at 17.3±5.5 mm from the lateral canthus, and then inferiorly, at 18.1±3.1 mm. The point of the zygomaticotemporal nerve appears at the margin of the zygomatic bone, 11.29±2.65 mm below the zygomaticofrontal suture and 21.76±2.76 mm from the superior border of the zygomatic arch. The inferior alveolar nerve in the mandibular canal runs above the lower one-third of the mandibular body. The terminal mandibular canal is located at an average of 4.5 mm under the mental foramen, advances 5.0 mm anteriorly, loops, and ends at the foramen. The facial nerve trunk is located 11 to 14 mm medial to the posterior border of the mandible. The trunk emerges out of the stylomastoid foramen and runs anteroinferiorly at an angle of 45°. The deep branch of the middle masseteric artery travels deep in the muscle, close to the periosteum of the mandible in 94% of cases. The average diameter is 1.23±0.26 mm. The masseteric nerve runs anteriorly and inferiorly between the deep and the middle layers of the masseter. It is observed at 33±5.6 mm from the inferior border of the muscle on the anterior third vertical line of the masseter muscle and at 47±5.5 mm in the posterior third.

Developmental changes in GABAergic and glycinergic synaptic transmission to rat motoneurons innervating jaw-closing and jaw-opening muscles.

Trigeminal motoneurons (MNs) innervating the jaw-closing and jaw-opening muscles receive numerous inhibitory synaptic inputs from GABAergic and glycinergic neurons, which are essential for oromotor functions, such as the orofacial reflex, suckling, and mastication. The properties of the GABAergic and glycinergic inputs of these MNs undergo developmental alterations during the period in which their feeding behavior proceeds from suckling to mastication; however, the detailed characteristics of the developmental patterns of GABAergic and glycinergic transmission in these neurons remain to be elucidated. This study was conducted to investigate developmental changes in miniature inhibitory postsynaptic currents (mIPSCs) in masseter (jaw-closing) and digastric (jaw-opening) MNs using brainstem slice preparations obtained from Wistar rats on postnatal day (P)2-5, P9-12, and P14-17. The frequency and amplitude of glycinergic mIPSCs substantially increased with age in both the masseter and digastric MNs. The rise time and decay time of glycinergic mIPSCs in both MNs decreased during development. In contrast, the frequency of GABAergic components in masseter MNs was higher at P2-5 than at P14-17, whereas that in the digastric MNs remained unchanged throughout the postnatal period. The proportion of currents mediated by GABA-glycine co-transmission was higher at P2-5, and then it decreased with age in both MNs. These results suggest that characteristics related to the development of inhibitory synaptic inputs differ between jaw-closing and jaw-opening MNs and between GABAergic and glycinergic currents. These distinct developmental characteristics may contribute to the development of feeding behaviors.

A Cadaveric Study of Dye Spreading: Determining the Ideal Injection Pattern for Masseter Hypertrophy.

BACKGROUND: Masseter hypertrophy is the main cause of an asymmetrical and squared lower facial contour in the Asian community. Botulinum toxin injection technique is crucial to treat this condition. OBJECTIVE: To improve injection techniques for masseter hypertrophy by elucidating the distribution of the injections within the masseter. METHODS: Thirty masseter muscles were divided into 6 groups of 5 muscles each. Each group received one 0.2- or 0.3-mL injection at Point A, B, or C according to a three-point technique. Muscle dimensions and dye of the primary and secondary dye spreading were measured. RESULTS: The average muscle length, width, and thickness were 69.87, 33.50, and 11.23 mm, respectively. The average primary longitudinal and horizontal spreading was 36.56 and 15.60 mm, respectively. No statistically significant difference was found between 0.2- and 0.3-mL injections at each point. CONCLUSION: The three-point technique best fits in the safe zone and should be the standard injection technique for masseter hypertrophy. Injection at Points B and C may create secondary spreading that affect the risorius muscle and the parotid gland which are the cause of asymmetrical smiling and xerostomia, respectively. The dosage should be adjusted according to the muscle volume and not only the thickness.

Constructing an adult orofacial premotor atlas in Allen mouse CCF.

Premotor circuits in the brainstem project to pools of orofacial motoneurons to execute essential motor action such as licking, chewing, breathing, and in rodent, whisking. Previous transsynaptic tracing studies only mapped orofacial premotor circuits in neonatal mice, but the adult circuits remain unknown as a consequence of technical difficulties. Here, we developed a three-step monosynaptic transsynaptic tracing strategy to identify premotor neurons controlling vibrissa, tongue protrusion, and jaw-closing muscles in the adult mouse. We registered these different groups of premotor neurons onto the Allen mouse brain common coordinate framework (CCF) and consequently generated a combined 3D orofacial premotor atlas, revealing unique spatial organizations of distinct premotor circuits. We further uncovered premotor neurons that simultaneously innervate multiple motor nuclei and, consequently, are likely to coordinate different muscles involved in the same orofacial motor actions. Our method for tracing adult premotor circuits and registering to Allen CCF is generally applicable and should facilitate the investigations of motor controls of diverse behaviors.

Acute Unilateral Masseter Muscle Paralysis Caused by Pontine Infarction.

In the present report, we discussed the case of a 57-year-old man with unilateral masticatory muscle weakness, nystagmus, skew deviation and facial hypesthesia due to pontine tegmental infarction. Trigeminal motor neuropathy attributed to brain infarction is very rare. Brain magnetic resonance imaging revealed a small dot-like infarction lesion in the pontine tegmentum. Masticatory muscle weakness was confirmed by an electrophysiological study performed on the day after admission in which there was an incomplete interference pattern without spontaneous denervation activity, suggesting that the patient's masseter muscle weakness was caused by an infarction of the trigeminal motor nucleus proper or trigeminal motor nerve fascicles rather than Wallerian degeneration of the trigeminal nerve or the progression of masseter muscle degeneration.

Predicting Resting Oral Commissure Tone Outcomes Following Masseter Nerve Transfer in Facial Reanimation.

Objective: To quantify the degree of oral commissure resting tone improvement in patients undergoing masseter to facial nerve transfer. Methods: A retrospective cohort study was completed in a tertiary academic medical practice. Consecutive cases of masseter nerve transfer patients within a patient database were evaluated from 6/2012 to 9/2017. Inclusion criteria were patients >18 years of age, with complete unilateral paralysis, receiving a masseter to facial nerve transfer, with at least 12 months of recovery, and possessing complete pre- and postoperative data. Patients were excluded if a simultaneous adjunctive procedure was performed so that tone could not be attributed to masseter transfer alone. The main outcome measure was the facial asymmetry index (FAI): the measured difference in distance between the medial canthus and oral commissure of the healthy and paralyzed sides. Results: Twenty-nine patients met inclusion and exclusion criteria and were further analyzed for this study. The oral commissure symmetry improved from 4.7 ± 2.8 mm preoperatively to 2.2 ± 2.3 mm postoperatively. In multivariate analysis, the preoperative FAI was the only significant predictive factor for improvement in commissure symmetry at rest (r = 0.589). This suggests that for each 1.0 mm of worse preoperatively oral commissure asymmetry, the improvement postoperatively was 0.6 mm. Age, gender, body mass index, side of paralysis, duration of paralysis, and recipient branch of facial nerve were not significant predictors in a multivariate analysis. Conclusion: Masseter to facial nerve transfer yields an estimated 60% correction in the oral commissure asymmetry. This estimation may be helpful in determining if adjunctive procedures should be utilized.

Anatomic landmarks for masseteric nerve identification: Anatomic study for a new reference point.

The masseteric nerve is often used as a donor nerve in the treatment of facial paralysis. Even if several anatomical studies described landmarks for its identification, their main disadvantages are the anatomical variability and the changes due to surgery. Sixteen dissections were performed on cadaveric specimens. The masseteric muscle (MM), the zygomatic arch (ZA), the masseteric nerve (MN) and the zygomatic branch of the facial nerve (ZB) were identified and their relationships were measured. The relationships between MN and ZB resulted to be constant, with MN intersecting ZB at a depth of 0,78 cm in the muscle, 1,6 cm below ZA and 0,8 cm from the posterior border of MM. The measures obtained demonstrated as the main zygomatic branch of the facial nerve can be a suitable landmark for the identification of the masseteric nerve, with no variations due to the surgical procedure or patient characteristics.

Combining an end to side nerve to masseter transfer with cross face nerve graft for functional upgrade in partial facial paralysis-an observational cohort study.

BACKGROUND: Results of a single stage technique combining cross facial nerve graft(s) (CFNG) with an ipsilateral end to side nerve to masseter transfer (NTM) in incomplete facial paralysis are assessed in a retrospective cohort study. The hypothesis is that the technique can safely improve the quality of smile in these patients. End to side coaptations for the recipient facial nerve minimise the risk of iatrogenic function loss, contrasting with the end to end neurorrhaphies used in conventional babysitting procedures. METHODS: A series of 27 patients was studied through case note review and standardised assessments. Surgical technique involves extensive exposure of the facial nerve and the NTM on the affected side and access is by bilateral preauricular incisions. End to end coaptations are made to the facial nerve on the donor side and on the recipient a standard CFNG is combined with an end to side NTM coaptation. Follow up was a minimum of 9 months from surgery. RESULTS: Overall improvement in the Sunnybrook scale averaged 33, from a pre-operative score of 40 (p < 0.05). Average upgrade of 4.7 mm of increased movement at the modiolus was achieved (p < 0.05), 43% improvement compared to the normal side. An improved resting symmetry of 3.8 mm was achieved in relevant cases. Where eye closure was strengthened the average improvement was 5 mm of increased lid closure. The smile achieved was spontaneous in 22 of 27 cases. CONCLUSION: The study confirms the hypothesis that CFNG with NTM transfer offers a physiological upgrade of facial movement in partial facial paralysis, applicable in both early and longstanding cases.

Dual innervation of free gracilis muscle for facial reanimation: What we know so far.

BACKGROUND: In the last decade, some institutions have begun combining the CFNG and masseteric nerve to provide dual innervation to the gracilis muscle for dynamic facial reanimation in facial paralysis patients. We reviewed the various ways that these two nerves have been coapted to provide dual innervation, and summarized the functional outcome for these methods. METHODS: A search of the Ovid EMBASE, MEDLINE, Cochrane, and Scopus databases was performed from 1946 to May 2019 for dual innervation of gracilis muscle using CFNG plus masseteric nerve for facial reanimation. RESULTS: A total of 184 articles were identified in the initial search, of which seven met our inclusion criteria. Three additional abstracts with 43 patients were identified but the level of details was not sufficient to include the results in the analysis. A total of 57 patients were reviewed (mean age of 42.1 years (6-79 years)). The majority of dual innervation procedures were performed using the ipsilateral masseteric nerve sutured end-to-end to the obturator nerve, and an additional CFNG connected end-to-side to the obturator nerve. In the 26 patients with Terzis scores available, there were no differences between masseteric nerve coapted end-to-end and CFNG as end-to-side to the obturator, or the reverse coaptation. All but two patients achieved function of the gracilis activated by the masseteric nerve within 2-5 months. CONCLUSIONS: This review shows that dual innervation of the gracilis is safe; and in some cases, does appear to provide early onset gracilis activation as well as an eventual spontaneous smile.

Masseteric-zygomatic nerve transfer for the management of eye closure-smile excursion synkinesis.

OBJECTIVE: The purpose of this study is to illustrate the efficacy of masseteric-to-zygomatic nerve transfer to address eye closure-smile excursion synkinesis after facial nerve paralysis. BACKGROUND: Synkinesis after facial nerve paralysis represents a wide range of facial movement disability. One manifestation is involuntary smiling with eye closure and a concomitant reduction of oral commissure movement with attempted smile ("frozen smile") - arising as a result of aberrant fibers populating the zygomatic branch-muscle complex. This is a particularly difficult area to treat with conservative management. We propose a single-stage procedure to sever the dysfunctional zygomatic nerve and perform a masseteric-zygomatic nerve coaptation to recover a voluntary smile. METHODS: We present a case series of eight patients with eye closure/smile excursion synkinesis who underwent single-stage masseteric-zygomatic nerve transfer by a single surgeon. The surgical technique and indications for surgery were reviewed. Patients underwent facial movement analysis using Emotrics. RESULTS: We analyzed the pre- and post- surgical photographic images of 8 patients with synkinesis (7 female, 1 male). Masseteric-facial nerve transfer was performed from 18 months to 22 years after the initial facial paralysis. Eyelid and brow positioning were more symmetric after surgery, with discrepancy between affected and unaffected side decreasing from 2.1 to 1.0 mm (p < .05) and 1.74 to 1.29 mm (p < .05), respectively. Symmetry of smile excursion postoperatively was also improved with commissure excursion discrepancy decreasing from 8.8 to 3.78 mm (p < .05). Discrepancy in the smile angle when comparing affected to unaffected side improved postoperatively from 10.3 to 5.2 degrees (p < .05). Improvement in oral commissure height was noted, but not statistically significant. CONCLUSIONS: The masseteric-zygomatic nerve transfer is a useful technique for the treatment of eye closure/smile excursion synkinesis after failure of chemodenervation and/or physical therapy.

Interference with SRF expression in skeletal muscles reduces peripheral nerve regeneration in mice.

Traumatic injury of peripheral nerves typically also damages nerve surrounding tissue including muscles. Hence, molecular and cellular interactions of neighboring damaged tissues might be decisive for successful axonal regeneration of injured nerves. So far, the contribution of muscles and muscle-derived molecules to peripheral nerve regeneration has only poorly been studied. Herein, we conditionally ablated SRF (serum response factor), an important myofiber transcription factor, in skeletal muscles of mice. Subsequently, the impact of this myofiber-restricted SRF deletion on peripheral nerve regeneration, i.e. facial nerve injury was analyzed. Quantification of facial nerve regeneration by retrograde tracer transport, inspection of neuromuscular junctions (NMJs) and recovery of whisker movement revealed reduced axonal regeneration upon muscle specific Srf deletion. In contrast, responses in brainstem facial motor neuron cell bodies such as regeneration-associated gene (RAG) induction of Atf3, synaptic stripping and neuroinflammation were not overly affected by SRF deficiency. Mechanistically, SRF in myofibers appears to stimulate nerve regeneration through regulation of muscular satellite cell (SC) proliferation. In summary, our data suggest a role of muscle cells and SRF expression within muscles for regeneration of injured peripheral nerves.

Dual Coaptation of Facial Nerve Using Masseteric Branch of Trigeminal Nerve for Iatrogenic Facial Palsy: Preliminary Reports.

OBJECTIVES: Immediate facial nerve substitution or graft technique has been used for the repair of facial nerve defects occurring as a result of tumour dissection. However, some patients report unsatisfactory outcomes, such as difficulty in maintaining resting or smiling symmetry, due to persistent flaccid facial palsy. Here we evaluated the functional outcomes of transferring the masseteric branch of the trigeminal nerve to the facial nerve adjunct to facial nerve graft. METHODS: We reviewed the medical records of seven patients who underwent facial reanimation surgery between 2014 and 2016. The patients were divided into two groups according to the type of facial reanimation surgery: group A, masseteric nerve innervation with interposition graft; group B, interposition graft only. The postoperative resting symmetry and dynamic movement were compared. RESULTS: Facial contraction was first observed in group A at 4 months and in group B at 7.3 months. Most of the patients achieved reliable resting symmetry; however, one patient in group B exhibited unsatisfactory facial weakness on the affected side. Group A patients showed better dynamic movement than group B patients. Eye closure, oral excursion and oral continence were better in group A than in group B patients. Smile symmetry in both groups was similar due to hyperkinetic movement in group A patients and flaccidity in group B patients. CONCLUSIONS: Dual innervation of the masseteric branch of the trigeminal nerve improves the dynamic movement of paralysed facial muscles and shortens the recovery period in patients with iatrogenic facial palsy.