LAUSR

INTRODUCTION Ossifying fibroma (OF) is a rare type of tumor characterized by fibrous tissue proliferation with cementum- or bone-like hard tissue formation. Since its first report by Montgomery in 19271), several cases of OF have been reported; however, no cases of OF arising from the zygomatic arch have been reported. Herein, we report a case of OF arising from the zygomatic arch. Clinical case summary: A 70-year-old female visited our department in February 2017 because of a gradually growing osseous protrusion in the right zygomatic region, which she was aware of since the previous 6 months. A 3.3 cm × 3.2-cm area of swelling was observed in the region. Computed tomography confirmed the presence of a granulated lesion on the surface of the right zygomatic arch. Accordingly, benign bone tumor was diagnosed, and tumor resection was subsequently performed. Histopathological analysis revealed irregularly arranged bone trabeculae, an increased number of fibroblasts, and collagen fibers between the bone trabeculae; accordingly, OF was diagnosed. No clinical or radiographic evidence of recurrence was observed during the 1.5-year follow-up period. DISCUSSION A granulated lesion was present on the surface of the right zygomatic arch, and the boundary between the lesion and surrounding bone was clear. Resection of the lesion from the zygomatic arch was relatively easy. Thus, OF was diagnosed. If OF is suspected, a risk of recurrence persists; therefore, shaving the area including the bones surrounding the lesion may be necessary. Although detailed causes of OF and osteoma remain unknown, past trauma has been indicated as a common etiology. However, compared with the frequency of fractures in the zygomatic arch, the frequency of OF and osteoma is rare; thus, the etiology of OF and osteoma remains to be fully elucidated.