WORKUP	Section 5 of 10
Author Information Introduction Clinical Differentials Workup Treatment Medication Follow-up Miscellaneous Bibliography

Imaging Studies:

• CT and MRI scans of the primary tumor may provide complementary findings.

• CT scan is superior to MRI in detailing cortical bone erosion and tumor mineralization.

• MRI is useful in providing views of the long axis of the limb and can sometimes depict the fatty nature of the tumor. However, liposarcomas may have low signals on T1W images and look similar to other soft tissue sarcomas.

• Angiography may demonstrate malignancy based on prominent vascularity and, thus, may be of value in planning surgical resection.

• Chest radiography may be used as initial screening for pulmonary metastases; however, the definitive modality used to detect pulmonary metastases is chest CT. CT scan of chest and abdomen may be needed to evaluate for extrapulmonary metastatic spread, which may be seen with myxoid liposarcoma.

Procedures:

• The diagnostic procedure of choice is open biopsy. Minimally invasive procedures have been advocated, such as fine needle aspiration, but experience with these modalities is limited, and results have been equivocal.

• For superficially located small fatty tumors, excisional biopsy is recommended for diagnosis.

• For larger (>3 cm) and deeper tumors, diagnosis and treatment may involve open incisional biopsy followed by definitive resection.

Several histologic subtypes exist; the 4 primary subtypes are well-differentiated, myxoid, round cell, and pleomorphic. Myxoid is the most common subtype and may be more common in children.

• Well-differentiated liposarcomas are composed of a heterogeneous organization of univacuolate adult lipocytes, chronic inflammatory cells, and fibrous connective tissue. This fibrous matrix harbors an arrangement of non–fat-storing stellate-shaped cells. Neoplastic cells with large hyperchromatic and pleomorphic nuclei are scattered within the region. Fat necrosis and mitosis usually are not observed. Dedifferentiated lesions may demonstrate a pattern of a densely cellular spindle-shaped sarcoma without fat accumulation.

• Myxoid liposarcomas occur in a variety of forms based on the degree of cellularity. Basic features of this subtype are (1) proliferating lipoblasts in various stages of differentiation, (2) delicate plexiform capillary patterns, and (3) a myxoid matrix containing abundant hyaluronidase-sensitive acid mucopolysaccharides. The least cellular pattern is a low-grade tumor harboring small spindle-shaped cells. These cells surround a plexiform vascular pattern that contrasts with a background of extracellular acid mucopolysaccharide. The most cellular pattern is that of a round-cell liposarcoma containing densely packed uniformly round cells that overcrowd the plexiform vasculature. In reality, most myxoid-type lesions show a mixture of the above features.

• Round-cell liposarcomas are associated with an aggressive clinical course and a high frequency of metastases. The primary feature is an excessive proliferation of uniform and rounded cells with little intercellular myxoid material. Occasionally, cells are arranged in branching rows and strands along abortive capillaries, resulting in a trabecular and adenoid appearance. Large pale polyhedral cells often give a hypernephroid appearance to the tumor.

• Pleomorphic liposarcomas display a disorderly growth pattern, a large degree of cellular pleomorphism, and several bizarre giant cells. Large giant cells may be observed harboring numerous lipid droplets of varying size, giving a moruloid appearance to the cells. Nucleoli vary in occurrence. Numerous small polygonal, round, and spindle-shaped lipoblasts can be observed intermingled with giant cells.

Histologic grade is stratified into 3 broad categories, namely, high, intermediate, and low grade.

• High-grade liposarcoma includes the pleomorphic and round-cell types.

• Intermediate-grade lesions encompass the poorly differentiated myxoid type.

• Low-grade liposarcomas include well-differentiated, myxoid, and lipomatous-type liposarcomas.

Staging: Staging for childhood soft tissue sarcomas follows the standard American Joint Committee on Cancer (AJCC) system, which is, unfortunately, of limited value. Liposarcomas do not spread to regional lymph nodes, and lymph node dissection is not indicated. Careful imaging is crucial in staging to assess size and presence or absence of metastases. Considering the possibility that a retroperitoneal or chest wall lesion may have a primary in the lower limb is important.

Grade or histologic subtype impacts significantly on prognosis, and an experienced pathologist needs to be involved. Myxoid liposarcomas that have more than 5-20% round-cell component have a worse outcome.

• The AJCC staging system is as follows:
  • G1 - Low grade

  • G2 - Intermediate grade

  • G3 - High grade

  • T1a - Noninvasive (<5 cm)

  • T1b - Noninvasive (>5 cm)

  • T2a - Invasive (<5 cm)

  • T2b - Invasive (>5 cm)

  • N1 - Regional nodes involved

  • M1 - Distant metastases

	TREATMENT	Section 6 of 10
Author Information Introduction Clinical Differentials Workup Treatment Medication Follow-up Miscellaneous Bibliography

Medical Care: Chemotherapy has been shown to be active in these tumors, but its role needs to be defined in clinical trials.

	MISCELLANEOUS	Section 9 of 10
Author Information Introduction Clinical Differentials Workup Treatment Medication Follow-up Miscellaneous Bibliography

Medical/Legal Pitfalls:

• While liposarcoma is an extremely rare lesion in the pediatric population, considering liposarcoma in the differential diagnosis of lipoma is important. Careful pathologic analysis of all excised specimens that clinically resemble lipoma is essential to avoid misdiagnosing a potentially lethal condition. The surgeon needs to place and orient the biopsy incision in a location that allows subsequent curative resection of the liposarcoma.