Retroperitoneal liposarcoma: sonographic findings

Discrimination of well-differentiated liposarcoma from benign lipoma on sonography: an uncontrolled retrospective study

PURPOSE

Well-differentiated liposarcoma, the most common subtype of liposarcoma, should be discriminated from benign lipoma. However, features on sonography for discriminating these two types of tumor have not been fully investigated. The present study was therefore aimed at clarifying differences in sonographic findings between well-differentiated liposarcoma and lipoma.

METHODS

The study population comprised 23 cases of well-differentiated liposarcoma and 181 cases of lipoma. We investigated differences in sonographic appearance and pathological findings between the two types of tumor.

RESULTS

Well-differentiated liposarcoma tended to develop more frequently in older patients and in the lower extremities including the gluteal region, compared with lipoma. Concerning sonographic findings, both tumors exhibited well-defined margins and heterogeneous internal echogenicity, including typical tiny striated hyperechoic lines. Well-differentiated liposarcoma was characterized by a higher frequency of the following findings compared with lipoma: (1) deep location, (2) irregular shape, (3) large diameter, (4) hyperechogenicity compared to surrounding tissue, and (5) presence of vascularity on Doppler sonography (p < 0.01 each). Notably, hyperechogenicity corresponded to the intermingled sclerosing component within the adipocytic component when sonographic findings were compared with those of pathology.

CONCLUSION

The present study suggests that several sonographic findings including hyperechogenicity and presence of vascularity might be key features for discriminating well-differentiated liposarcoma from lipoma.

Sonographic Appearances of Liposarcoma: Correlations with Pathologic Subtypes

Liposarcoma is the second most common malignant soft-tissue tumor. This entity is pathologically categorized into 4 subtypes: well-differentiated, myxoid, dedifferentiated and pleomorphic. Although features on magnetic resonance imaging and computed tomography for these 4 subtypes have been reported quite precisely, those on sonography have not been fully investigated. The present study was therefore aimed at clarifying the sonographic appearances of each liposarcoma subtype and assessing correlations with histopathology. The study population was made up of 35 cases, including 21 cases of well-differentiated liposarcoma, 6 cases of myxoid liposarcoma, 6 cases of dedifferentiated liposarcoma and 2 cases of pleomorphic liposarcoma. Compared with the other subtypes, well-differentiated liposarcoma was characterized by the high frequency of the following findings: isoechogenicity, tiny hyperechoic lines and hypovascularity (p < 0.01, in each). Myxoid liposarcomas were characterized by low echogenicity, intermingled with anechoic areas and moderate vascularity (p < 0.01, in each). Dedifferentiated liposarcomas showed a specific biphasic pattern of hyperechoic and hypoechoic areas and hypervascularity (p < 0.01, in each). Pleomorphic liposarcomas showed a specific gyrus-like mixture of hyperechoic and hypoechoic areas (p < 0.01). In conclusion, the present study revealed different characteristics of sonographic appearance among the 4 histopathologic subtypes of liposarcoma.

From the archives of the AFIP: imaging of musculoskeletal liposarcoma with radiologic-pathologic correlation

Liposarcoma is the second most common type of soft-tissue sarcoma, accounting for 10%-35% of these lesions. The World Health Organization has categorized soft-tissue liposarcomas into five distinct histologic subtypes: well differentiated, dedifferentiated, myxoid, pleomorphic, and mixed type. Well-differentiated liposarcomas frequently demonstrate a diagnostic appearance on computed tomographic (CT) or magnetic resonance (MR) images, with a largely lipomatous mass (>75% of the lesion) and nonlipomatous components in thick septa or focal nodules. The CT or MR imaging finding of a nodular dominant focus (>1 cm in size) of nonlipomatous tissue in a well-differentiated liposarcoma suggests dedifferentiated liposarcoma, and biopsy should be directed at the nonadipose component. The high water content of myxoid liposarcoma seen at pathologic analysis and constituting the majority of the lesion is reflected at sonography, CT, and MR imaging. However, the detection of a small amount of adipose tissue in the septa or as small nodular foci superimposed on the background of myxoid tissue allows prospective diagnosis in 78%-95% of myxoid liposarcomas. Pleomorphic liposarcomas are high-grade sarcomatous lesions and typically appear as heterogeneous soft-tissue masses, although small amounts of fat are seen on MR images in 62%-75% of cases, findings that suggest the diagnosis. Mixed-type liposarcomas have features representing a combination of the other subtypes. Primary liposarcoma of bone is exceedingly rare and usually demonstrates aggressive nonspecific features, although fat may be seen. Understanding and recognition of the spectrum of appearances of the various types of musculoskeletal liposarcoma, which reflect their underlying pathologic characteristics, improves radiologic assessment and is vital for optimal patient management.

[Retroperitoneal liposarcoma. Case report]

We report one case of retroperitoneal liposarcoma treated by surgery and radiotherapy. With the literature, we discuss the pathologic and therapeutic aspect of this lesion.