Factors Associated With Paradoxical Masseteric Bulging After Botulinum Toxin Injection for Masseter Hypertrophy: A...

Botulinum neurotoxin (BoNT) injection is the preferred minimally invasive treatment for masseter hypertrophy, but paradoxical masseteric bulging (PMB) is a distressing complication. How to clinically prevent and avoid the development of PMB remains a key concern for injecting physicians.

This study collected ultrasound and injection data from 22 PMB masseter muscles and 66 non-PMB masseter muscles between September 2024 and January 2025. Univariate analysis was used to compare imaging and injection-related parameters between the two groups, including masseter prominence, masseter thickness, deep inferior tendon (DIT) type, DIT thickness, intraoperative tactile sensation, and injected agent.

Univariate analysis showed significant intergroup differences in masseter prominence grade, DIT type, DIT thickness, masseter thickness, injection dosage, and intraoperative tactile sensation (all p < 0.05). The PMB group had greater masseter thickness (13.30 ± 0.171 mm vs. 10.32 ± 0.169 mm), thicker DIT (0.85 [0.348] mm vs. 0.60 [0.208] mm), and a higher incidence of fascial penetration sensation than the control group.

Preoperative ultrasound assessment of masseter and DIT characteristics, combined with individualized layered injection and intraoperative tactile feedback, effectively mitigates PMB risk. Ultrasound-guided precise supplementary injection is the preferred intervention for PMB management.