A 40-year-old man with no past medical history presents with four months of mild right leg pain that had progressed in the last three weeks.
Plain X-ray films show a lytic lesion with a thick sclerotic rim within the proximal tibia. The cortex was intact. The lesion showed a lucent area with trabecular thickening and coarse septa but no calcified matrix was seen(Fig.1)
Computed tomography (CT) demonstrated a centric bone lesion that causes mild bone expansion without disrupting the cortex. Within the lesion, CT images show a predominant low homogeneous fluid attenuation content with a rim of sclerotic bone; no calcified matrix was seen. Extensive areas with a low CT attenuation coefficient resulting from fatty content were enclosing the lesion.(Fig.2)
At magnetic resonance (MR) imaging, the lesion showed predominantly an isointense signal on T1-weighted images surrounded by a thin hyperintense rim. PD SPIR weighted fat suppressed MR showed a hyperintense lesion with thin hypointense margins. No associated extraosseous soft-tissue mass nor bone-marrow oedema were seen on MR images.(Fig.3a and 3b)
Lipomas associated with bone can be classified according to their intraosseous, cortical, or parosteal location. Intraosseous lipomas are rare [2].
The common sites for this lesion include the intertrochanteric and subtrochanteric regions of the femur and calcaneus, but they may arise from marrow fat in any skeletal bone.
They commonly present in the middle-aged population, with a slight male predominance [1].
Intraosseous lipomas are frequently incidental findings but they can cause pain or swelling as in our case [1].
In most cases, the imaging characteristics of this entity when they are considered together with the clinical history, could be pathognomonic making biopsy unnecessary.
To recognize the imaging features of intraosseous lipomas it is important to understand the histopathology [1].
Milgram classified intraosseous lipoma in three categories [3].
Stage 1:solid lesion of viable lipocytes.
Stage 2:areas of partial fat necrosis and focal calcification with persistent viable lipocytes.
Stage 3:advanced cell necrosis of the lesion with variable amounts of calcification, cyst formation and reactive new bone formation.
The radiographic appearance may show lucent areas with a well-defined benign-appearing osteolytic bone lesion, often with radiodense areas of dystrophic calcification. Expansile remodeling of bone might be seen. The tumour may be associated with thick sclerotic borders[1].
CT and MR imaging demonstrate the fatty component of the lesion which is diagnostic for intraosseous lipoma.
In an early stage, a CT may show resorption of the bone trabeculae with areas of lucency corresponding to fat attenuation. Some lesions may appear with patchy areas of calcification and fat necrosis. Stage 3 intraosseous lipomas exhibits resorption of trabecular bone and predominantly central calcification with reactive peripheral ossification and cyst formation caused by necrosis of the fat component, as in our case [1].
MR Imaging findings include fat signal intensity similar to that of subcutaneous fat[1]. With involution, fibrous proliferation and cystic degeneration may develop and might be the predominant finding showing variable fluid signal intensity on T1- and T2- weighted sequences, as shown in our case [1].
The finding of an intraosseus lytic lesion that demonstrates mild expansile remodeling with a sclerotic rim and peripheral fat tissue margins was consistent with a stage 3 intraosseus lipoma with advanced cell necrosis and cystic degeneration.
Malignant transformation is very rare but it has been described [4].
Surgical treatment may be required for symptomatic lesions.
Intraosseous lipoma of the proximal tibia
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Based on the provided X-ray, CT, and MRI images of the right leg, there is a relatively well-defined osteolytic lesion located in the tibial shaft or near the metaphyseal region, showing mild expansile change and a sclerotic margin. CT demonstrates that the lesion is primarily composed of fat density, with partial calcification or cystic changes. On MRI, the lesion mainly appears as hyperintense signal (T1-weighted) similar to subcutaneous fat, and hyperintense or mixed signal (T2-weighted). Local cystic changes and residual fat components suggest fat necrosis, fibrosis, or calcification. There is some thickening and sclerosis of the surrounding cortex, without evidence of pathological fracture or significant soft tissue involvement.
Taking into account the patient’s middle-aged status, location of the lesion, slight pain progression over four months, and the imaging findings—clear fat signals, sclerotic margin, cystic changes, and calcifications—the most likely diagnosis is:
Intraosseous Lipoma (Stage 3), accompanied by fat necrosis and cystic changes.
If further confirmation is needed, a biopsy may be considered. However, the classic imaging presentation typically ensures a high diagnostic accuracy.
Treatment for intraosseous lipoma primarily depends on the patient’s clinical symptoms and the degree of imaging changes:
Regarding rehabilitation and exercise prescriptions, these should be individualized based on the patient’s preoperative or postoperative status, pain level, and bone stability, following a gradual approach:
Throughout the rehabilitation process, closely monitor local pain and bone stability, follow a gradual, personalized approach, and collaborate with orthopedic surgeons and rehabilitation therapists as needed.
This report provides reference analyses based on the currently available imaging and clinical information and cannot replace an in-person consultation or the opinion of a qualified physician. The actual treatment plan should be determined by a specialist following a comprehensive assessment of the patient’s specific condition.
Intraosseous lipoma of the proximal tibia
