The Risorius Muscle: Anatomic Considerations With Reference to Botulinum Neurotoxin Injection for Masseteric Hypertrophy

BACKGROUNDThe botulinum neurotoxin Type A (BTX) injection into the masseter muscle often causes a change in the facial expression. There is as yet no precise anatomic evidence to support this etiologic factor of constrained facial expressions. OBJECTIVEThe aim of this study was to clarify the locati...

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Published inDermatologic surgery Vol. 40; no. 12; pp. 1334 - 1339
Main Authors Bae, Jung-Hee, Choi, Da-Yae, Lee, Jae-Gi, Seo, Kyle K, Tansatit, Tanvaa, Kim, Hee-Jin
Format Journal Article
LanguageEnglish
Published United States by the American Society for Dermatologic Surgery, Inc. Published by Lippincott Williams & Wilkins 01.12.2014
Subjects
Adult
Aged
Aged, 80 and over
Botulinum Toxins, Type A - therapeutic use
Cadaver
Dissection
Facial Expression
Facial Muscles - anatomy & histology
Female
Humans
Hypertrophy - drug therapy
Injections
Male
Masseter Muscle - pathology
Middle Aged
Neuromuscular Agents - therapeutic use
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Summary:BACKGROUNDThe botulinum neurotoxin Type A (BTX) injection into the masseter muscle often causes a change in the facial expression. There is as yet no precise anatomic evidence to support this etiologic factor of constrained facial expressions. OBJECTIVEThe aim of this study was to clarify the location and boundaries of the risorius muscle and its topographical relationship with the surrounding structures. MATERIALS AND METHODSThis study involved the dissection of 48 hemifaces. The locations of origin and insertion points of the risorius muscle were measured, and the masseter muscle was divided into 6 equally sized rectangular areas. RESULTSCases where the masseter muscle was covered by the risorius muscle were classified into the following 4 typesin Type A, Area III was partially covered by the risorius (17.8%); in Type B, Area VI was partially covered (20.0%); in Type C, Areas III and VI were partially covered (53.3%); and in Type D, Areas II, III, and VI were covered (6.7%). CONCLUSIONThese findings suggest that the medial part of the masseter muscle represents a hazard zone into which the injection of BTX may affect the risorius muscle, potentially resulting in iatrogenic unnatural facial expressions.
ISSN:1076-0512
1524-4725
DOI:10.1097/DSS.0000000000000223