MR imaging of muscles of mastication.

High-field MR imaging was used to study structural and physiologic alterations involving the muscles of mastication in 46 patients. Muscular abnormalities were often detected incidentally in conjunction with lesions of the CNS, cranial nerves, facial bones, and/or temporomandibular joint (TMJ). Specific pathologic alterations observed included anomalies of musculoskeletal development, muscle hypertrophy, atrophy (disuse and denervation), inflammatory disorders, injuries (including contusions, tears, and muscle rupture), posttraumatic musculoskeletal deformities, and reflex sympathetic dystrophy. Atrophy, fatty replacement, fibrosis, and contracture of selected muscles of mastication may accompany internal derangement of the TMJ in the absence of traumatic deformity. We conclude that MR is a highly accurate imaging method for detecting masticatory muscle disease. Nontraumatic anatomic and physiologic abnormalities of the muscles of mastication are uncommon disorders. Demonstrable muscle alterations frequently accompany fracture dislocations of the mandibular condyle neck and related facial bones onto which masticatory muscles attach.