Liposarcoma




Well-Differentiated, Myxoid/Round Cell, Pleomorphic, and Dedifferentiated Subtypes


CLINICAL SUMMARY


Liposarcoma is the second most common soft tissue sarcoma after undifferentiated sarcoma, and is further subdivided into several distinctive subtypes. It can present as a low-grade or high-grade tumor, with prognosis corresponding to grade. While treatment always includes surgical excision, the use of adjuvant radiation and chemotherapy depends on the subtype, location, and grade.


DIAGNOSTIC FEATURES


















History


  • Most common between ages 40 and 60 years



  • Very rare in children



  • Painless, enlarging mass

Location


  • Most common in proximal extremities



  • Also occurs in retroperitoneum

MRI


  • Appearance varies by subtype



  • Well-differentiated liposarcoma is closest in appearance to lipoma, with predominantly high T1 signal



  • Myxoid/round cell liposarcoma has high water content, reflected as diffusely high signal on T2 MRI



  • Dedifferentiated liposarcoma demonstrates two distinct regions: a background of well-differentiated liposarcoma and a region appearing as a nonspecific soft tissue sarcoma, with a low T1 and high T2 signal, respectively




LIPOSARCOMA SUBTYPES





Well-Differentiated Liposarcoma





  • Well-differentiated liposarcoma is a slow-growing lipomatous tumor that never metastasizes but can recur locally, sometimes repeatedly. It is the most common variant, making up 40% to 45% of liposarcomas.



  • Despite the similarity in appearance between lipomas and well-differentiated liposarcomas, the two tumors can be distinguished with careful evaluation of the MRI imaging. In particular, only 4% to 9% of well-differentiated liposarcomas show thin septa, whereas the majority demonstrates thick septa or nodular nonlipomatous components.



  • In the retroperitoneum, any lipomatous tumor should be considered a liposarcoma. In contrast to liposarcomas in the extremity, retroperitoneal well-differentiated liposarcomas can cause significant mortality and even morbidity, due to repeated local recurrence. The rate of dedifferentiation in the retroperitoneum is approximately 20%, compared to less than 2% in the extremities.
































  • CT scans of well-differentiated liposarcomas in the medial thigh ( left ) and in the retroperitoneum ( right ) appear as low-attenuation, fatty masses.



  • While the density closely approximates subcutaneous fat, nonlipomatous thick septations and nodularity differentiate both tumors from lipomas.










  • T1 MRI of a well-differentiated liposarcoma in the calf ( left ) demonstrates fatty high signal with prominent septation.



  • The fat-suppressed T2 image ( right ) accentuates the nonlipomatous component.










  • T1 postgadolinium MRI demonstrates patchy enhancement of the nonlipomatous areas ( left ).



  • A sectioned gross specimen ( right ) demonstrates predominant fatty tissue in large lobules (L) and prominent septa ( arrow ).










  • Grossly, these tumors appear similar to normal fat. Some tumors may contain areas of hemorrhage, as seen in this example ( left ).



  • Low-power histology demonstrates predominantly mature adipose tissue ( right ).


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