Surgical Correction of Unilateral Masseteric Hypertrophy with Mandibular Angle Overgrowth in an Adolescent by Mandibular Angle Ostectomy and Masseter Myectomy: A Case Report

Unilateral masseter hypertrophy and mandibular angle overgrowth is a very rare condition that causes marked facial asymmetry, especially when it occurs in adolescents. The deformity is caused by the prominence of muscle mass and the bony prominence of the gonial angle. It may sometimes cause aesthetic concerns and mild functional problems, such as discomfort in mastication. Although botulinum toxin injection can provide temporary relief for unilateral masseter hypertrophy, it does not correct the bony prominence and therefore requires surgical correction. This case report is about a 15-year-old male who presented with progressive left-sided facial asymmetry because of prominent mandibular angle and hypertrophic masseter muscle. Clinical evaluation showed unilateral prominence of the left mandibular angle, which was more prominent on clenching, with hypertrophy of the masseter muscle. Radiographic analysis, which included Orthopantomogram (OPG) and Posteroanterior (PA) skull view showed prominence and asymmetry of the left mandibular angle, which was suggestive of overgrowth. There was no history of trauma, systemic disease, parafunctional habits, or previous treatment. The surgical procedure was performed under general anaesthesia through an extraoral approach, with mandibular angle ostectomy and masseter myectomy. The postoperative course was uneventful, with resolution of oedema over time showing improvement in facial symmetry, streamlined gonial contours, and harmony without complications. The surgical approach resulted in satisfactory early aesthetic and functional improvement by addressing both the osseous and muscular components of the deformity. At 1-month follow-up, improved facial symmetry and mandibular contour were observed without postoperative complications.