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Parosteal lipoma is a rare and generally asymptomatic benign tumor of mature adipose tissue that is located in direct apposition to the external surface of the bone. These tumors are occasionally associated with reactive changes in the underlying bone. The reactive bone formation is generally restricted to the base of the tumor, that is, near the periosteum. We recently experienced a case of parosteal lipoma in the proximal femur, which displayed exuberant bone and cartilage formation, and this led us to a misdiagnosis of chondroblastic osteosarcoma on the initial biopsy. We report here on this case with a special emphasis on making the differential diagnosis from osteosarcoma.


Parosteal lipoma is a rare and generally asymptomatic benign tumor of mature adipose tissue that is located in direct apposition to the external surface of the bone. These tumors are occasionally associated with reactive changes in the underlying bone. The reactive bone formation is generally restricted to the base of the tumor, that is, near the periosteum. We recently experienced a case of parosteal lipoma in the proximal femur, which displayed exuberant bone and cartilage formation, and this led us to a misdiagnosis of chondroblastic osteosarcoma on the initial biopsy. We report here on this case with a special emphasis on making the differential diagnosis from osteosarcoma.