Anat Cell Biol.  2024 Mar;57(1):13-17. 10.5115/acb.23.234.

Sonographic observation of the paradoxical masseteric bulging and clinical implication of functional compartment

• Yi KH
• Bae H
• Kim SB
• Kim WR
• Lee W
• Kim JS
• Kim HJ

• KMID: 2554236
• DOI: http://doi.org/10.5115/acb.23.234

Abstract

Masseter are commonly botulinum neurotoxin targeted muscle for facial contouring in aesthetic field. However, paradoxical masseteric bulging is common adverse effect that has not been discussed with ultrasonographic observations. Retrospective study has been conducted from October, 2021 to January, 2023, out of 324 patients have done blinded botulinum neurotoxin injection in the masseter at the middle and lower portion of the masseter with each side of 25 units (letibotulinum neurotoxin type A), 3 patients demonstrated paradoxical masseteric bulging has been reported and the image observed by ultrasonography by physician. Based on the observations made, we can infer that the function of the moving muscle involves twisting of the muscle fibers during contraction, along with the twisting of the deep inferior tendon, which causes the muscle to be divided into anterior and posterior compartments rather than into superficial and deep compartments of masseter. In ultrasonographic observe the skin surface of a patient with paradoxical masseteric bulging, it is observable that either the anterior or posterior part contracts significantly. The functional units of anterior and posterior compartment are observable as muscular contraction of inward movement of the muscle from either the anterior or posterior functional unit.

Keyword

Paradoxical masseteric bulging; Functional compartment; Masseter muscle; Deep inferior tendon; Ultrasonography

Figure

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  Fig. 1 The placement of the probe of ultrasonography has been place in the line connecting ear lobe and cheilion.

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  Fig. 2 The area within the masseter muscle at rest (A) and when contracted (B) can be depicted by the highlighted sections in red and blue. The red shading indicates the front portion of the masseter muscle, while the blue shading indicates its rear section.

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  Fig. 3 The compartment of masseter muscle when in resting (A) and contracted (B) status as the following of compartment as shaded by red and blue areas. Red shaded area represents anterior part of the masseter muscle and blue shaded area represents posterior part of the masseter muscle.

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  Fig. 4 The region within the masseter muscle during relaxation (A) and contracted (B) is represented by highlighted red and blue sections. The red shading signifies the anterior part of the masseter muscle, while the blue shading represents its posterior section.

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  Fig. 5 The paradoxical masseteric bulging has been observed with ultrasonography, the acts with the anterior part and superficial part at the middle portion of masseter. In posterior and deep part of the masseter muscle contracts together. Adapted from Ultrasonographic anatomy of the face and neck for minimally invasive procedures : an anatomic guideline for ultrasonographic-guided procedures. Springer, 2021, with permission [8].

Reference

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