Intraosseous lipomas are rare and benign tumors of unclear etiology. Most of them are asymptomatic, being accidentally diagnosed during imaging tests performed for other reasons and they usually have unspecific clinical presentations. Radiographically, they can be confused with other entities as non-ossifying fibromas or simple cysts. Methods. We report two cases, a 39-year-old and a 25-year-old Caucasian female patients, referred to our hospital with a mass in the proximal third of the right tibia and distal femur respectively with slowly progressive growth. In conventional X-ray images and computed tomography, a well-defined, expansive intraosseous lytic lesion without cortical disruption was observed in both cases. Magnetic resonance imaging demonstrated predominance of lipomatous tissue signal, being compatible with intraosseous lipoma. The patients underwent excision of the tumor, confirming the diagnosis of intraosseous lipoma after pathological study. Results. In the immediate postoperative period, swelling and pain decreased and at the 6th-month postoperative follow-up the patients are asymptomatic and without radiographic signs of recurrence. Discussion. Intraosseous lipomas are tumors that can go easily unnoticed, being difficult to diagnose on conventional X-ray images. Because of that, other imaging tests, such as CT and MRI, are necessary for diagnosis and histopathology for confirmation. Conservative treatment in asymptomatic patients and surgery in symptomatic cases is recommended. Recurrence and malignant transformation of these tumors is rare.

Intraosseous lipomas are rare and benign tumors of unclear etiology. Most of them are asymptomatic, being accidentally diagnosed during imaging tests performed for other reasons and they usually have unspecific clinical presentations. Radiographically, they can be confused with other entities as non-ossifying fibromas or simple cysts. Methods. We report two cases, a 39-year-old and a 25-year-old Caucasian female patients, referred to our hospital with a mass in the proximal third of the right tibia and distal femur respectively with slowly progressive growth. In conventional X-ray images and computed tomography, a well-defined, expansive intraosseous lytic lesion without cortical disruption was observed in both cases. Magnetic resonance imaging demonstrated predominance of lipomatous tissue signal, being compatible with intraosseous lipoma. The patients underwent excision of the tumor, confirming the diagnosis of intraosseous lipoma after pathological study. Results. In the immediate postoperative period, swelling and pain decreased and at the 6th-month postoperative follow-up the patients are asymptomatic and without radiographic signs of recurrence. Discussion. Intraosseous lipomas are tumors that can go easily unnoticed, being difficult to diagnose on conventional X-ray images. Because of that, other imaging tests, such as CT and MRI, are necessary for diagnosis and histopathology for confirmation. Conservative treatment in asymptomatic patients and surgery in symptomatic cases is recommended. Recurrence and malignant transformation of these tumors is rare.