Cartilaginous metaplasia in giant fibrolipoma – a rare case report

The most common benign tumors of the mesenchyme are the lipomas. Lipomas can arise in any location in which fat is present. Different histopathological variants of lipoma have been described including fibrolipoma and chondrolipoma. Chondrolipoma is a rarely encountered diagnosis and is considered as a cartilaginous metaplasia in lipomas of large size. Given the rarity of this condition, we describe here a case of giant fibrolipoma with cartilaginous metaplasia in thigh of an elderly male patient.


Introduction
Lipomas are benign, well circumscribed, connective tissue neoplasms. They usually present as slow growing, solitary and asymptomatic, subcutaneous or superficial lesions [1]. Most patients affected by lipomas are in their fifth or sixth decade of life, and only rarely are children affected [2]. Different variants of lipoma have been described, such as fibrolipoma, angiolipoma, myolipoma, spindle cell lipoma, chondroid lipoma, chondrolipoma and osteolipoma [1,3]. Fibrolipoma is characterized by the presence of prominent bundles of mature fibrous tissue traversing the fatty lobules [2]. Cartilaginous or osseous metaplasia (chondrolipoma and osteolipoma) is rare and is mainly encountered in lipomas of large size and long duration [3].

Case Report
A 59 year old male patient presented to the surgery department with history of swelling in the left thigh for last three years. Examination revealed a large mass in anterolateral aspect of left thigh, which was nontender, soft in consistency, noncompressible with well-defined margins. The swelling was not fixed to the skin or underlying structures. After the surgical resection of this mass, the histopathology section of ourlaboratory received a single well encapsulated fibrofatty tumor mass measuring 14×12 × 4 cms and weighing about 640 grams. Cut surface of the mass was lobulated, yellow with myxoid appearing areas at places ( Figure 1). The tumor mass was sliced in further parallel ways but no areas of hemorrhage or necrosis were noted. Multiple representative bits were taken from the tumor mass and processed conventionally for paraffin embedded tissue sections.

Discussion
The etiology of lipomas is unclear. They have been reported to be both sporadic and inherited [4]. For a lipoma to be referred to as "giant", the lesion should be at least 10 cms indiameter [2]. In our case, the lipoma was of 14 × 12 × 4 cms in size. Fibrolipomas may develop in virtually any region that contains fat, but in general, they tend to appear on trunk, neck, and upper extremities. The fibrolipoma with cartilaginous metaplasia of our case was located in thigh.
Chondrolipoma is the mature adipocytic lesion displaying cartilaginous metaplasia (mature cartilage). It is an infrequent occurrence, which is predominantly observed in large-sized, long-standing lipomas [5]. The cartilaginous metaplasia observed in lipoma of our case was also of large size (14 cms in largest dimension) and of long-standing duration (3 years). There is a terminologically similar entity known as Chondroid lipoma. It is a benign adipose tissue tumour which contains a chondroid matrix, fat and lipoblasts. Both clinicians and pathologists should be aware of the terminological (but not histological) similarity between chondrolipomas and chondroid lipomas [6].
According to previous case reports, chondrolipomas arise mostly from the breast [7] or from head and neck region [1,6]. The occurrence in extremities is extremely rare and very few case reports of chondrolipoma are available to the best of our knowledge [5, [8][9][10].
The malignant transformation of a lipoma into a liposarcoma is rare as is the sarcomatous transformation of giant lipomas. It is important to differentiate giant lipomas from liposarcomas, malignant fibrous histiocytoma and other benign soft tissue lesions [4]. Indeed, the main concern in the diagnosis of giant lipomas should be the exclusion of malignancy [2]. In our case after extensive sampling, the tumour mass revealed features of fibrolipoma with cartilaginous metaplasia. No evidence of any malignant transformation was noted.

Conclusion
Chondrolipomas are rare with very few cases reported in the literature. Being well demarcated in nature, makes them easily resectable by surgery and they do not recur. The additional presenceof giant fibrolipoma makes it a unique case report.
This case highlights the importance of extensive sampling in cases of giant lipomas to detect it's variants, associated metaplasias and to rule out malignancy.