Answer 3. Liposarcoma

영상소견에서 뚜렷한 Fat이 안보이는 liposarcoma 증례

Case A: DEDIFFERENTIATED  LIPOSARCOMA  WITH  MYOGENIC  DIFFERENTIATION,    20.0 x 14.0 x 12.0 cm,  RETROPERITONEUM,  ( See  note )

       with  1)  mitosis:  up  to  18/10 HPF.

             2)  necrosis:  not  identified.

             3)  no  involvement  of  kidney,  spleen,  large  intestine  and

                 pancreas  parenchyma.

             4)  clear  external,  pancreatic,  large  intestinal  proximal

                 and  distal  resection  margins.

             5)  no  metastasis  in  2  regional  lymph  nodes  ( 0/2 )

: - The  results  of  immunohistochemical  staining:

     CD117,  ( - );  CD34,  ( - );  SMA,  ( + );  desmin,  ( + );     MDM2,  ( + ); 

CDK4,  ( + );  S-100,  ( - );     Ki-67  labeling  index,  ( about  40 % ).

Case B

Cut  surface:  yellowish  white,  myxoid  with  focal  necrosis

MALIGNANT  SPINDLE  CELL  NEOPLASM,  CONSISTENT  WITH 

DEDIFFERENTIATED  LIPOSARCOMA

Liposarcoma is the most common primary retroperitoneal malignant soft tissue tumor and is divided into five subtypes,

1. well differentiated,

2. dedifferentiated,

3. myxoid,

4. pleomorphic,

5. mixed types according to the 2002 WHO histologic classification of soft tissue tumors

    

Dedifferentiated liposarcoma(DDL) is a high-grade nonlipogenic sarcoma that arises in the background of a preexisting well-differentiated liposarcoma. Dedifferentiated liposarcoma has a worse prognosis than other subtypes because it has a higher risk of local recurrence and distant metastasis.

DDL is a bimorphic neoplasm in which a well-differentiated liposarcoma is juxtaposed with a high-grade nonlipogenic sarcoma. On histopathology and CT images, the areas of well-differentiation contain fatty component. On the other hand, the areas of dedifferentiation display more various components. The most common dedifferentiated component is undifferentiated pleomorphic sarcoma (previously called malignant fibrous histiocytoma) or fibrosarcoma; however, rhabdomyosarcomatous, leiomyosarcomatous, or osteosarcomatous component were also included in 10% of the cases..

So on CT, Adipose tissue (below 30 HU), soft tissue (34~76 HU) and the tissue with borderline density can be observed in DDL mass. Calcification or ossification has been reported as a sign of dedifferentiation. An enhancing or centrally necrotic nodule may be indicative of a dedifferentiated component in DDL. On MRI, the most of dedifferentiated component of DDL typically have nonspecific findings, low to intermediate signal intensity on T1-weighted MR images and intermediate to high signal intensity on T2-weighted MR images.

Conclusion

Dedifferentiated liposarcomas present various spectra of imaging findings. It may appear as other types of liposarcoma or other malignant retroperitoneal tumor.