Primary hemosiderotic fibrolipomatous tumor in bone: a case report and review of the literature.

Background and aim: Hemosiderotic fibrolipomatous tumor (HFLT) is a locally invasive tumor composed of mature adipocytes accompanied by spindle cells containing hemosiderin deposition. In 2013, it was categorized by WHO as a soft tissue tumor with uncertain differentiation. So far, the literature has reported 60 cases but primary HFLT in bone has never before been reported. We set out to investigate the clinicopathological features of primary HFLT in bone. Methods: We retrospectively reviewed the clinical, imaging, histological, and immunophenotypic features and treatment of 1 case of primary HFLT in bone, and combined this with literature discussion. Results: HFLT occurred in the lateral femoral condyle of a 50-year-old male patient, which might have been overlooked were it not for the knee-joint pain and dysfunction. CT and MRI showed osteolytic bone destruction with a clear 4.0-cm diameter boundary, diagnosed as cystic damage of the lateral condyle of the left femur. SPECT metabolism was not active. Histologically, the lesion was composed of different proportions of mature fat cells, spindle cells, and hemosiderin. Immunohistochemistry revealed spindle cells expressing vimentin, p63, but not CD34, calponin, and others. The tumor tissue was thoroughly removed by curetting, and a bone graft was carried out after immersion in anhydrous ethanol. At the 11-month postoperative follow-up, the patient was recovering well. Conclusions: Primary HFLT in bone is extremely rare. In imaging, it can easily be misdiagnosed as a bone cyst. Histological morphology of the current case is similar to that of soft tissue HFLT.