Paradoxical masseteric bulging after botulinum neurotoxin type A injection

Area of Science:

• Medical Aesthetics
• Facial Anatomy
• Neuromodulator Therapy

Background:

• Botulinum neurotoxin type A injections are commonly used for masseter muscle reduction.
• Paradoxical masseteric bulging is an uncommon adverse effect where the muscle protrudes post-injection.
• This may result from incomplete toxin diffusion due to internal muscle structures.

Observation:

• A clinical case of paradoxical masseteric bulging is presented in a female patient in her late 40s.
• The adverse effect occurred within a week following botulinum neurotoxin type A injections into the masseter muscle.
• The patient experienced unexpected protrusion contrary to the intended muscle weakening.

Findings:

• The study identifies an inferior tendon structure within the superficial masseter as a potential cause for incomplete toxin diffusion.
• This anatomical variation can divide the masseter into superficial and deep bellies, hindering uniform treatment.
• The paradoxical bulging is a direct consequence of localized, uninhibited muscle activity.

Implications:

• Understanding masseter muscle anatomy is crucial for successful botulinum neurotoxin type A treatments.
• A modified two-site injection technique is proposed for effectively managing paradoxical masseteric bulging.
• This technique aims to improve toxin distribution and achieve desired aesthetic outcomes while mitigating adverse effects.