Case report: Recurrent parosteal lipoma at Dr. Moewardi hospital.

Background: Parosteal lipoma is a rare and benign neoplasm originating from mature adipose tissue near the periosteum. Clinically, it is difficult to diagnose due to its similarity to the clinical manifestation of sarcoma, so imaging, histopathology, and immunohistochemistry examinations are necessary. Case presentation: A 54-year-old woman presented with lump on the right thigh that had gone through surgery eight years prior, with a diameter of 20 cm, with a partly hard and partly soft consistency, the patient was diagnosed with suspected recurrent liposarcoma. We performed wide excision and histopathological results showed a proliferation of bone cells and cartilage cells that were lobulated, surrounded by a proliferation of fat cells with no pleomorphism or immature cells. Discussion: Parosteal lipomas are neoplasms derived from adult adipose tissue, usually connected to the periosteum, and rare and benign. Two theories of pathogenesis of parosteal lipomas. (1) tumors arise from the differentiation of stem cells derived from adipose tissue, (2) the tumor is derived from secondary metaplasia of fibroblasts due to recurrent trauma, metabolic changes, or ischemia. Based on the theory, it is likely that in this case is due to the presence of differentiation of adiposa tissue due to the non-acquisition of a history of trauma. Conclusion: Parosteal lipoma is a rare case of benign neoplasm, which is difficult to diagnose clinically due to its similar sarcoma, thus requiring imaging and histopathological examination. The treatment of choice is wide excision by taking the entire tumor to prevent a recurrence.