A peripheral osteoma of the mandibular coronoid process

Osteoma is a benign neoplasm composed of mature bone and is limited almost exclusively to the craniofacial bones. Osteoma of the coronoid process is very rare. We encountered a 35-year-old woman who noticed right cheek pain when opening her mouth. She was referred to our hospital in August 2021 for the further evaluation and treatment of radio-opacity of the right mandibular coronoid process. She had no relevant medical history, family history, or history of oral parafunction. Initial extra- and intraoral clinical examinations revealed no definite swelling and no limitation of joint motion. However, the maximum unassisted mouth opening was 37 mm, and she experienced pain in the medial mandibular ramus at mouth opening. After this discomfort she had been pain-free for 15 years. Panoramic radiography revealed mushroom-shaped radiopacity on the right-side mandibular coronoid process which had increased in size compared to 15 years earlier. Computed tomography showed a bone-like lesion on the right mandibular coronoid process measuring 28 × 18 × 15 mm, with lesion-shaped right skull base bone resorption. The clinical diagnosis was a benign osseous neoplasm of the coronoid process (right side). The lesion was excised intraorally under general anesthesia; the pathological diagnosis was compact bone osteoma. The postoperative course was uneventful. The patient was then able to open her mouth to 40 mm and her right cheek pain at mouth-opening had disappeared. There has been no recurrence as of 2 years post-surgery.