Paradoxical bulging of muscle after injection of botulinum neurotoxin type A into hypertrophied masseter muscle

摘要

A square face, commonly as a consequence of masseter muscle hypertrophy and/or prominent mandibular angle, is a cosmetically unpleasant condition especially in Asian female populations. As preferences on minimally invasive procedures are growing in cosmetic surgery, treatment with botulinum neurotoxin type A (BoNT-A) has recently become one of the most requested procedures instead of conventional surgery in lower face contouring. Reported undesirable effects after injection of BoNT-A, such as masticatory difficulty, facial asymmetry and unnatural smiling appearances, are usually induced by unwanted pharmacologic action of BoNT-A on masseter or adjacent muscles.1^3 In this report, we try to focus on a common but easily overlooked discomfort, muscular bulging after injection of BoNT-A into hypertrophied masseter muscle.