Myositis ossificans traumatica(MOT) in head and neck area is a rare non-neoplastic, heterotopic bone formation within a muscle, arising after trauma or surgery. Although the several case reports have described the occurrence of MOT in other muscles of oro-facial musculature, MOT has never been reported in mentalis muscle. We demonstrate a case of MOT occurred in mentalis muscle of a 64 years old male. He recently complained of a movable mass with no pain. He had experienced a hitting trauma on his right anterior mandible about 25 years ago. Since then, the trauma area has been asymptomatic. The lesion showed severe muscular degeneration, resulted in a pseudocystic change without epithelial lining. The ectopic ossification was closely associated with the fibrous fascia of adjacent muscles. The lesion contained a lot of basophilic materials admixed with atrophying cells, which were supposed to be derived from muscle parenchyma injured previously. It was presumed that the basophilic materials induced callus-like ossification in the fibro-muscular lesion, also recruited macrophages and fibroblasts. However, the ossification processes in MOT were predominantly characterized by dystrophic calcification without osteoblastic differentiation of mesenchymal cells. Even more, there appeared some skeletal muscle bundles which were calcified dystrophically. Therefore, we suggest the present case of MOT might be initiated by dystrophic calcification in the degenerating muscle tissue

Focal myositis is a rare disease associated with inflammatory changes invading the skeletal muscles and may be triggered by nerve lesion. We describe a case of 33-year-old woman who was diagnosed focal denervation myositis of piriformis and gluteal muscles associated with sciatic neuropathy because of severe uterine enlargement due to twin pregnancy misdiagnosed as lumbar herniated nucleus pulposus. MRI is one of the key diagnostic tools in the assessment of focal denervation myositis for differential diagnosis. Nonsteroidal anti-inflammatory drugs are commonly used for treatment of focal myositis. Spontaneous regression is obtained in numerous cases.