An intramuscular lipoma-like lesion in the cheek following gingival flap surgery with human recombinant fibroblast growth factor 2 for periodontal disease

Intramuscular lipoma is uncommon in the oral region, and its etiology is unknown. REGROTH® is a periodontal tissue regenerative medicine containing recombinant fibroblast growth factor 2 (FGF-2). In this report, we present a case of intramuscular lipoma-like lesion developed in the right cheek. A 49-year-old Japanese male was referred to our hospital in September 2020 with a chief complaint of painless swelling of the right cheek. About 1 year before the visit, he underwent flap surgery for a periodontal disease of the right lower second molar at the nearby dental clinic. The alveolar bone defect in the second molar was filled with a total amount of the REGROTH Dental Liquid Kit 600 μg® and covered with the gingival periosteal flap. Two months later, however, diffuse swelling with redness was observed from the operated right lower molar area to the cheek. The diffuse swelling improved with anti-inflammatory treatment, and then recurred repeatedly, eventually a large mass of the cheek remained. The imaging and surgical findings at our hospital showed that unencapsulated tumor was surrounded by the masseter and buccinator muscles, was in close contact with the buccal side of right lower molars. Tumor was histologically an intramuscular lipoma infiltrating the surrounding muscle tissues. The occurrence of this lesion adjacent to the flap operation site in the short postoperative period suggests that the surgical operation using the REGROTH® is involved in the tumor development.