Keywords

1 Definition

  • An exceedingly rare malignant intraosseous neoplasm, constituted of adipose cells, which can also arise on the surface of bone.

2 Etiology

  • Unknown.

  • It may arise from preexisting lipomas.

3 Epidemiology

  • Liposarcoma of bone is an exceedingly rare tumor.

  • It can be seen at any age but is more common in adults.

  • There is a slight male predominance.

4 Sites of Involvement

  • Almost all cases reported are in the long bones, especially the femur and tibia.

5 Clinical Symptoms and Signs

  • Pain and the presence of a mass are the usual symptoms.

  • Pathological fracture may occur.

6 Imaging Features

  • Radiographs show a lucent mass that may or may not present well-defined margins, including cortical permeation (Fig. 45.1).

  • CT and MRI of the tumor show features characteristic of fat tissue (Fig. 45.2).

Fig. 45.1
figure 1

(a, b) Radiographs of a liposarcoma of the femur. Uncharacteristic lucent mass in the medullary compartment, with some endosteal scalloping and undefined limits

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Fig. 45.2
figure 2

CT scan of surface liposarcoma of the proximal femur. Well-circumscribed lucent lesion distorting the host bone external shape

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7 Imaging Differential Diagnosis

  • The nonspecific imaging findings of liposarcoma in bone can be seen in various other benign and malignant bone lesions.

8 Pathology

8.1 Gross Features

  • The cut surface shows a lobulated, yellow to white, and soft or firm lesion, with well-defined or poorly defined margins.

  • It is usually a large lesion.

  • Some lesions may present myxoid, mucinous features.

8.2 Histological Features

  • Similar to soft-tissue variants of liposarcomas:

    • Atypical lipomatous tumor/well-differentiated liposarcoma

      • Neoplastic tissue is very similar to normal fat.

      • Atypical nuclei may be seen, mostly in or near the spindle cell septae that traverse the neoplasia (Figs. 45.3, 45.4, 45.5, and 45.6).

      • A few lipoblasts are also seen.

    • Dedifferentiated liposarcoma

      • Abrupt transition from low-grade lipogenic area to high-grade non-lipogenic morphology is seen within a well-differentiated liposarcoma.

      • May have heterologous elements.

    • Myxoid liposarcoma

      • It may be constituted by two neoplastic tissue patterns: a richly arborizing, vascularized myxoid pattern and a round cell pattern.

      • Patterns may be seen alone or in variable mixture in a particular tumor.

    • Pleomorphic liposarcoma

      • Highly anaplastic fat cells characterize this variant (Fig. 45.7).

Fig. 45.3
figure 3

Low-power microscopic view of well-differentiated liposarcoma

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Fig. 45.4
figure 4

Medium-power microscopic view of well-differentiated liposarcoma. Atypical cells are more easily found in the spindle cells septae of the lesion

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Fig. 45.5
figure 5

High-power microscopic view of well-differentiated liposarcoma. There may be only a few atypical cell nuclei. Multivacuolated adipocytes and lipoblasts are also seen

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Fig. 45.6
figure 6

High-power microscopic view of well-differentiated liposarcoma. Multiple atypical nuclei in adipocyte

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Fig. 45.7
figure 7

Medium-power microscopic view of pleomorphic liposarcoma

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9 Pathologic Differential Diagnosis

9.1 Lipoma

  • It may be difficult to differentiate from well-differentiated liposarcoma in a limited sample.

10 Ancillary Techniques

  • MDM2/CDK4 are usually positive together or individually in liposarcomas. Pleomorphic liposarcomas differ from the dedifferentiated variant by expressing only one marker.

  • FABP4/aP2, a recently reported sensitive adipocytic marker, is strongly positive.

10.1 Genetics

  • Supranumerary ring or long marker chromosomes are found in well-differentiated liposarcomas.

  • Translocation t(12;16) is common in myxoid/round liposarcoma. Fusion of DDIT3 (CHOP) and FUS (TLS) genes. Translocation t(21;22) rarely.

  • Amplification of 12q14.2–21.2 includes the HMGA2 and MDM2 gene regions.

  • Various aberrations of 12q13–15 were described in lipomas.

  • Pleomorphic liposarcomas present complex karyotypes.

  • Amplification of 1q21.2–31.2 was described in a parosteal liposarcoma.

  • Abnormalities in the AKT genes were found to correlate with the clinicopathological profile of tumors.

11 Prognosis

  • Well-differentiated and myxoid liposarcoma, the two most common types, have a more favorable prognosis than the other histological types.

12 Treatment

  • Wide resection or amputation.

  • Any type of liposarcoma, including well-differentiated, can metastasize. Follow-up and screening are required.