Selective Neurectomy of the Masseteric Nerve in Masseter Hypertrophy

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.

Topographic anatomical localization of the motor nerve entry points (MEPs) of the masseter muscle

PURPOSE

The masseteric nerve, which is a branch of the mandibular nerve, passes lateral to the mandibular notch and then spreads in the muscle to achieve motor innervation. The muscle entry points of these motor branches are the target points of minimally invasive interventions preferred in the treatment of masseter hypertrophy. The aim of this study was to reveal the areas where the motor entry points are concentrated in the muscle by dividing the muscle into topographic regions using reliable anatomic landmarks.

METHODS

Bilateral 20 masseter muscles (40 in total) belonging to 20 formalin-fixed cadavers (10 female and 10 male) were examined. The distribution of the nerve in the muscle and its motor entry points were demonstrated and marked on the muscle surface. The masseter muscle was divided into six areas by lines passing through reliable anatomical landmarks (Areas 1-6).

RESULTS

The total number of MEPs was 231.The mean distance of the MEPs from the Line-1 was 27.4 ± 11 mm, and the same distance from the Line-6 was 30.32 ± 7.2 mm. Most of the MEPs (123/231) were located in Area-4. Area-6 was the second (82/231) and Area-5 (19/231) was the third.

CONCLUSION

We suggest that interventions in Area-4 (especially in the middle part) may have less complications as a result of less relationship with surrounding anatomical structures and more effective with high MEP number.

The Premasseteric Branch of the Facial Artery: A Review and Translation of Adachi's Work

The premasseteric branch of the facial artery is a variable posterior branch that is closely associated with the anterior border of the masseter muscle. Since its first description, the premasseteric branch has been described using different terms such as the masseteric or posterior branch of the facial artery. While the artery’s anatomy is known, it is infrequently discussed in the literature. This manuscript reviews the artery’s origin, course, and importance during maxillofacial procedures, especially those involving manipulation of the masseter. We also provide a translation of Adachi’s 1928 German text describing the branch.

Endoscope-Assisted Avulsion of the Masseter Nerve Attached to the Temporomandibular Joint Disc for the Treatment of Hemimasticatory Spasm: A Report of Two Cases

OBJECTIVE

Hemimasticatory spasm (HMS) is a rare masticatory muscle disorder. Drug therapy, microvascular decompression, and botulinum toxin have had varying efficacy and adverse effects. We have reported the cases of 2 patients who had undergone a novel therapy for HMS, based on endoscope-assisted nerve avulsion of the masseter nerve attached to the temporomandibular joint (TMJ) disc.

METHODS

We performed a retrospective study of 2 patients with HMS who had undergone surgery from June 2014 to June 2017 at the oral surgery department of Shanghai Ninth People's Hospital affiliated to Shanghai JiaoTong University School of Medicine. Both patients had undergone endoscope-assisted avulsion of the masseter nerve attached to the TMJ disc. Both patients were evaluated by electromyography postoperatively and were followed up for 36 months after surgery.

RESULTS

Both patients had had all the signs and symptoms of HMS. The HMS had resolved immediately after surgery. At 1 week after surgery, electromyography revealed that the high-frequency group discharge potential in the motor unit accompanying the spasm was no longer present, and the effect was maintained for the 36-month follow-up period. These results indicated a good curative effect. Electromyography also showed strength weakness and mild shape atrophy of the masseter muscle on the affected side.

CONCLUSIONS

Endoscope-assisted avulsion of the masseter nerve attached to the TMJ disc showed a good curative effect, little trauma, few complications, and a quick postoperative recovery. It could be used as an alternative treatment of HMS for selected patients.

Segmental masseteric flap for dynamic reanimation of facial palsy

The masseter muscle is one of the major chewing muscles and contributes to define facial contour. It is an important landmark for aesthetic and functional surgery and has been used for facial palsy reanimation or as source of donor motor nerve. We present an anatomic study to evaluate the possibility of using a muscle subunit for dynamic eye reanimation. Sixteen head halves were dissected under magnification to study the neurovascular distribution and determine safe muscle subunits; areas of safe/dangerous dissection were investigated. Once isolated, the arc of rotation of the muscular subunit was measured on fresh body to verify the reach to the lateral canthus. The patterns of neurovascular distribution and areas of safe dissection were identified; the anterior third of the muscle represents an ideal subunit with constant nerve and artery distribution. The muscle is too short to reach the lateral canthus; a fascia graft extension is needed. The information provided identified the main neurovascular branches and confirms the feasibility of a dynamic segmental flap. The need of efficient motor units for facial reanimation demands for different surgical options. A detailed anatomic description of the neurovascular bundle is mandatory to safely raise a functional motor subunit.

Variable presentation of temporalis hypertrophy — A case report with literature review

A case of painful, initially bilateral, and then unilateral temporalis hypertrophy in a 33-year-old Caucasian woman is presented in a primary care setting; the aetiology of the hypertrophy was considered reactive in nature. Medical and supportive treatment was successful in providing symptomatic relief. Further treatment including an intramuscular botulinum injection was considered by the patient with a view to reduction of the chronic enlargement of her temporalis and masseter musculature. A review of the literature and previous treatment regimes is also presented.