Botulinum toxin type A (BoNT-A) injections in the forehead region should only target the frontalis. This study applied ultrasonography with the aim of providing guidelines for predicting the layered structure and soft-tissue thickness of the forehead. We performed ultrasound scanning at 7 facial landmarks in 40 Korean adults. Allowing for the error range, the minimum depth from the skin to exclude the muscle layer was 2.3 mm, and the maximum depth from the skin to include the muscle layer was 2.8 mm. Of the total 7 points from the skin to muscle surface, significant differences between the males and females were found in 6 points (p < 0.05). Clinicians can use ultrasonography to identify the structural layers of the scalp. Even if ultrasound-guided injections are not performed, it is possible to target only muscle layers in BoNT-A injections by maintaining a needle depth of around 2.5 mm.
Keywords: Botulinum toxin type A; Forehead; Frontalis; Soft tissue thickness; Ultrasonography.
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