Anatomical evaluation of facial nerve pathways and dissection of "premasseter space" for rhytidectomy in Asians.

[BACKGROUND] Partial detachment of the superficial musculoaponeurotic system (SMAS) by dissection of the premasseter space (PMS) is an option for enhancing the effectiveness of SMAS-based rhytidectomy. The aim of this study was to identify the underlying cause of the potential risk of motor nerve impairment sometimes caused by PMS dissection and to consider the effective use of PMS dissection, especially in Asians.

[METHODS] Detailed dissection was carried out on six fixed Japanese cadavers to evaluate facial nerve pathways around the PMS.

[RESULTS] The anterior wall of the PMS was opaque because each face exhibited fibers of various thicknesses within and around the anterior border of the masseter. The ascending ramifications of the buccal trunk ran through the fibers, outside the anterior border of the masseter in some faces but within it in others.

[CONCLUSIONS] This study revealed the presence of a danger zone when dissecting the PMS in Asians. Severing the fibers that fix the SMAS to the masseter fascia around the anterior border of the masseter is sometimes unavoidable to attain good mobility of the SMAS. Surgeons must be mindful of the fibers near the anterior border of the masseter because they may be outside the PMS and contain buccal trunk ramifications; the anterior wall of the PMS tends to be opaque in Asians. Nonetheless, the extent of PMS dissection should be determined on an individual basis. The present findings may help to reduce relevant risks in Asian patients and standardize procedures for effective rhytidectomy.

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