Parosteal lipoma is an unusual kind of lipoma and occurs in intimate association with the underlying periostium of the bone. Parosteal lipomas mostly affect the long bones and involvement of the mandible is rare. We report a case of ossifying parosteal lipoma of the mandible in which CT was effective in diagnosis and showed a well-circumscribed mass of fat attenuation containing areas of ossification and branch-like bony protuberances from adjacent cortical bone. Microscopic examination revealed that the mass was composed of mature fat cells without nuclear hyperchromasia or atypia. Layers of bone and ossification were found inside. Although rare, it should be considered as a differential diagnosis of teratoma, osteochondroma and osteosarcoma. Dentomaxillofacial Radiology ( Keywords: lipoma; mandible; pathology; computed tomography
Case reportHistory and clinical examination A 48-year-old male was referred to our hospital because of a slow-growing mass on his chin which had been present for at least 20 years with associated occasional numbness of the right lower lip. The patient's general health was good and no other remarkable medical history could be elicited.A mass of approximately 86665 cm in dimension was palpable beneath the skin of the chin and mental areas extending bilaterally to the buccal areas. The mass was soft, non-tender and fixed to the mandible. No prominent swelling, hyperaemia or ulceration of the skin was seen. No mouth opening difficulty was noted. Intraoral examination showed that the buccogingival sulcus was shallower and the mucosa was intact. No prominent loosening of the mandibular teeth was noted.
Radiographic examinationA panoramic radiograph failed to find any major bony changes of the mandible. CT revealed a broad-based, well-demarcated mass with fat attenuation beneath the skin (Figure 1a). Areas of ossification were prominent inside the mass (Figure 1b). Exophytic osseous protuberance and branch-like periosteal thickening from the underlying symphysis of the mandible were identified (Figure 1a,c). The cortical bone was uneven and was locally infiltrated or depressed. The marrow space of the mandible was not contiguous with the lesion and sclerosis of the trabeculae was seen.
Surgical treatmentEn bloc resection of the mass together with the osseous protuberance from the mandible was performed. The mass was well circumscribed and was easily dissected from the adjacent soft tissue. The base of the tumour adhered strongly to the underlying mandible. The mass measured 76565 cm and was well encapsulated by a thin, fibrous membrane. The cut surface of the specimen was yellowish with a mostly homogeneous appearance. Hard bony protuberance from the underlying mandible was chiselled and the bone was shaped.