A 15-year-old female patient presents at the Maxillofacial Surgery Department of the San Borja Arriarán Hospital Complex with painless right facial asymmetry, which has progressively evolved over time without any other symptoms.
During the interview, the patient reported no history of morbidities or surgery. Nor does she report any habitual use of drugs or allergies. No type of parafunction was detected.
On extraoral examination there is an increase in volume in the region of the right mandibular angle with poorly defined limits. On palpation it was firm, painless and showed no signs of inflammation or submandibular or cervical lymph node involvement. No pathological signs or symptoms are detected in the TMJ examination.

The intraoral examination showed nothing relevant in relation to the soft tissues, teeth and occlusion. Salivary secretion was normal, especially in relation to the Stenon's ducts.
A panoramic X-ray was requested, showing a much more marked right mandibular angle. The lateral skull X-ray showed a double mandibular contour and the frontal teleradiography showed that the right mandibular sector was more developed, with no impact on the occlusal plane. In addition, bone scintigraphy was performed to rule out condylar hyperplasia and electromyography.

The diagnosis was unilateral right maseterine hypertrophy, so it was decided to resect the right mandibular angle extraorally.
Under general anaesthesia, a right mandibular subangle access was performed until the ipsilateral angle was exposed. The angle and a portion of the masseter muscle were resected. A biopsy of the excised muscle was performed and the report did not reveal any pathological tissue condition.
The patient was monitored immediately after the operation and showed no complications. After 6 years, the patient is in good condition with no recurrence.

