Age / Sex : 38 / M

Chief complaint: right knee swelling for 9 month

1) What is your impression?

Two weeks later, you can see the final diagnosis with a brief discussion of this case.

(Quiz는 quiz일 뿐이오니 답안은 한개만 보내주시기 바라오며, 복수의 답안을 보내주시는 분은 정답이 포함되어 있더라도 부득이 semi-correct answer로 처리토록 하겠습니다.)

Myxoid liposarcoma

Discussion

Findings:

MR images show multilobulated and septated huge mass in the intermuscular area of the posterior aspect of distal thigh. Lacy or amorphous high SI within predominantly low SI mass on T1 WI, and predominatly high SI on T2 WI. The mass shows heterogeneous enhancement On fat-suppresed enhanced T1WI, There is no evidence of infiltration or invasion into adjacent structures

Differential Diagnosis:

Myxoid liposarcoma

Synovial sarcoma

Myxofibrosarcoma

Diagnosis:  

Myxoid liposarcoma

Discussion:

Myxoid liposarcoma is the second most common type of liposarcoma, representing 30%–40% of all liposarcomas in the extremities. Myxoid liposarcomas occur most commonly in the lower extremity, particularly the thigh. Myxoid liposarcomas occur in the intermuscular fascial planes or deep-seated areas. They are rarely found in the subcutaneous tissue.

Because the fat content is often less than 10%–25% of the tumor volume, MR imaging may not show the typical features of a lipomatous tumor. A myxoid liposarcoma that contains abundant water can mimic a cystic lesion, producing diagnostic confusion.

Myxoid liposarcomas exhibit low signal intensity on nonenhanced T1-weighted images and high signal intensity on T2-weighted images. On T1-weighted images, most myxoid liposarcomas exhibit high-signal-intensity foci within a predominantly homogeneous low-signal-intensity mass. These foci represent fat within the tumor and usually appear lacy or linear and amorphous rather than solid. The absence of high-signal-intensity foci on T1-weighted images makes a myxoid liposarcoma indistinguishable from most other cystlike masses. US is useful in differentiating solid masses from cystic lesions. The enhancement patterns of the myxoid liposarcomas could be classified into three groups: homogeneous (total enhancement), heterogeneous(partial enhancement), and no enhancement.

References

Mi-Sook Sung,  Heong S. Kang,  Jin S. Suh,  et al. Myxoid liposarcoma : Appearance at MR imaging with histologic correlation. RadioGraphics 2000;20:1007–1019