Application of magnetic resonance imaging and ultrasonography to preoperative evaluation of masseteric hypertrophy.

A case of unilateral masseteric hypertrophy in a 30-year-old man is described. Preoperative evaluation was performed by magnetic resonance imaging (MRI), computed tomography (CT) and ultrasonography (USG). MRI could delineate not only the border between medial and lateral layers of the masseter but also delineate the hypertrophic portion. MRI also provided more information in respect of the masseter muscle as well as the other masticatory muscles and the surrounding tissues than CT. USG was useful because of its real-time processing, especially in this case where facial asymmetry was emphasized during mastication. We resected the medial lower-half of the masseter intraorally based on these imagings and obtained a successful result.