Osteochondrolipoma of the Mandible

CASE REPORT

A 72-year-old man presented with a 20-year history of a slow-growing painless mass at the mental region. On examination, there was a single, well-defined, mobile, relatively hard mass, with normal surrounding skin and mucosa (Fig 1).

Figure 1. Clinical view of the lesion at first presentation.

Computed tomographic scan showed an elliptically shaped smooth mass of fat density measuring 2×1.5 cm with partial ossification. The mass was not in contact with the mandible, and a clinical diagnosis of lipoma with calculus was made (Fig 2).

Figure 2. Computed tomographic scan shows a smooth mass of partial calcification at the mental region.

Under local anesthesia, the tumor with no adhesions to the periosteum of the mandible was easily dissected through the intraoral incision. Gross examination showed a whitish, partially yellowish mass measuring 2×1.5×1.5 cm, with a well-circumscribed smooth surface (Fig 3). Histological examination showed that the tumor was mostly composed of mature adipose tissue with partially osseous and cartilaginous differentiation. No atypical cells or mitotic figures were observed. Immunohistochemical staining of the tumor was positive for CD34. On the basis of these findings, the tumor was diagnosed as an osteochondrolipoma (Fig 4). Six months after surgery, there was no recurrence of the disease.

Figure 3. Macroscopic findings of the lesion. A soft yellowish mass together with a hard whitish nodule is seen.

Figure 4. Histological and immunohistochemical findings of the specimen. (a) Predominant adipose tissue with osseous and cartilaginous differentiation (H&E, ×40). (b) Immunohistochemical stain showing positivity with CD34 (×100).

DISCUSSION

Lipomas are very common benign soft-tissue tumors that are normally found at the back, neck, shoulders, abdomen, or proximal extremities.^1,2 They occasionally contain other mesenchymal components such as bone, cartilage, and vessels, and they are called osteolipoma, chondrolipoma, and angiolipoma, respectively. Among them, osteolipoma and chondrolipoma are rare, especially lipoma with both osseous and cartilaginous components. That is, osteochondrolipoma is extremely rare and to the best of our knowledge, only 14 cases have been reported in the English literature, including the present case (Table 1); 5 tumors were localized at the maxillofacial region,^5-8 with another 5 cases at the extremities,^2,4,9,12,13 and the other 4 at the trunk.^1,3,10,11 There was no clear sex predominance (8 men, 6 women), and the average patient age was 57.4 years (SD = 13.5 years; range, 19-73 years). The clinical history is usually that of a painless, slow-growing mass, sometimes measured in years (mean >5 years, ranging from 1 month to >20 years). Average tumor size was 4.2 cm (SD = 2.5 cm; range, 0.5-9.5 cm).

The nomenclature of osteochondrolipoma is controversial. Jones et al¹⁴ defined a tumor composed of 2 or more mature mesenchymal tissues, with no single element predominating, as mesenchymoma. In contrast, because the reported tumors including the present case had mature fatty tissue as the predominant component, it is appropriate to consider them osteochondrolipomas. However, there is no clear border between benign mesenchymomas and osteochondrolipomas.³

The pathogenesis of osteochondrolipomas remains uncertain. Different theories have been proposed to explain the formation of cartilaginous and osseous tissues in lipomas.⁶ One theory suggests that adipose, cartilaginous, and osseous components originate from multipotent undifferentiated mesenchymal cells independently.¹⁵ A second theory suggests that cartilaginous and osseous components may represent a metaplastic process in preexisting lipoma^3,16 or chondrolipoma.¹² Katzer³ suggested that, because the adipose tissue predominates in chondrolipomas and osteolipomas, and one can see different stages of the formation of cartilage and bone simultaneously, the pathogenesis of chondrolipomas and osteolipomas as primary mixed tumors is improbable. Recently, it has been shown that pluripotent adult stem cells, the adipose-derived stem cells, obtained from liposuction waste have the potential for chondrogenesis, osteogenesis, and myogenesis.^17,18 As in the present case, CD34 was positive and pluripotency of the tumor was suggested. Considering that lipoma cells might have the potential to differentiate into other mesenchymal tissues, it would be surprising that most lipomas are pure lipomas without showing multidirectional differentiation.

The differential diagnosis should include osteocartilaginous choristoma, metastatic chondrosarcoma or osteosarcoma, liposarcoma with metaplasia, and posttraumatic chondrification.¹⁹ Because an incisional biopsy, which samples only a part of the lesion, can lead to misdiagnosis due to the pleomorphism of osteochondrolipoma, submission of the whole tumor for histopathological examination following exenteration is the preferred approach to diagnosis and treatment. No recurrences have been reported.