Giant Peripheral Osteoma of the Mandibular Antegonial Notch in an Elderly Patient: A Case Report

Peripheral osteoma is a benign bone tumor that frequently arises in the craniofacial skeleton. In the mandible, it usually involves the body or condyle, whereas lesions at or near the antegonial notch are extremely rare, particularly when they are large and occur in elderly patients. This report describes the case of an 80-year-old man who presented with an asymptomatic hard swelling in the left submandibular region. The maximal interincisal mouth opening was approximately 40 mm, which was within normal limits, and there was no mandibular deviation. Imaging revealed a pedunculated, homogeneously radiodense mass measuring 50 × 45 × 40 mm arising from the cortical surface of the left mandibular antegonial notch without cortical destruction or associated soft tissue mass. The lesion was removed en bloc via an extraoral submandibular approach together with a thin margin of normal cortical bone, and the markedly thinned mandibular cortex was reinforced with a titanium plate. Histopathological examination showed dense lamellar bone with small marrow spaces and no cellular atypia, consistent with compact-type peripheral osteoma. The postoperative course was uneventful apart from transient weakness of the marginal mandibular branch of the facial nerve, and no recurrence has been observed during 15 months of follow-up. In this case, the exact onset and growth rate of the lesion could not be determined because previous radiographs were unavailable, and relatively rapid enlargement over a short period could not be excluded. Chronic mechanical stimulation and local circulatory changes in the masseter region may have contributed to tumor development and growth; however, their roles remain speculative. This case highlights the importance of considering peripheral osteoma in the differential diagnosis of unilateral mandibular swelling, especially in atypical locations, and underscores the utility of detailed imaging evaluation and long-term postoperative surveillance.