Teaching Case

A 60-year-old female patient complained of a rapid growing lump on the left calf, painless and without skin alterations. No significant personal or family medical history were reported.

A small parts ultrasound was performed and detected a vascularized mass on the left calf in the posterior muscular compartment. MRI was performed for better characterization. T1WI (Fig. 1a) shows high-signal-intensity foci of fat within a predominantly low-signal-intensity mass. T1 with fat suppression imaging shows suppression of the signal in the foci that showed high signal on T1WI, representing fat within the lesion (Fig. 1b). Sagittal T2FS (Fig. 1c) shows a hyperintense mass with some hypointense bands. There is exuberant soft tissue edema surrounding the lesion. Post-contrast study shows heterogeneous enhancement with a cotton-like appearance (Fig. 1d).
After surgery with complete resection and adjuvant chemotherapy, the patient maintained remission for 5 years. At this point, in a control CT, a lytic lesion was detected in left iliac bone. MRI of this region was performed for better characterization (Fig. 3), which raised the suspicion of bone relapse, confirmed by biopsy.

Myxoid liposarcoma is the 2nd commonest type of liposarcoma following well differentiated liposarcoma. It represents 30-40% liposarcomas of extremities with typical lower limb location (75-80%). The age of appearance varies from 18-67 years, without gender predilection, but extraordinarily rare in patients less than 10 years of age. [1]
Myxoid liposarcomas are large, well-defined, and multilobulated lesions predominantly hypointense on T1WI due to myxoid component (water-rich), with hyperintense bands of fat. On T2WI are markedly hyperintense and surrounding edema is usually present.
Post-contrast imaging shows heterogeneous (cotton-like) or marked homogeneous enhancement. The myxoid matrix may simulate a cystic lesion (10-20%), therefore the importance of contrast administration. Necrotic areas may be present.[2]
The pathognomonic feature is the adipose tissue seen in the mass. MRI is superior to CT in this important depiction. Fat usually constitutes 10-20% of the lesion and is often seen in septa or small nodules. About 90-95% of myxoid liposarcomas demonstrate fat at MR imaging. Careful comparison of T1 and T2WI and the use of fat-suppression techniques is of major importance in the detection of adipose content.[1, 2]

Histologically the tumour consists of well-delineated lobules of myxoid tissue, a delicate arborizing capillary network and lipoblasts (Fig. 2). Areas of mature adipose tissue are usually present but sparse. Genetically it is characterized by the reciprocal translocation t(12;16)(q13;p11) - highly specific and sensitive, since it is not associated with other myxoid tumours (myxofibrosarcoma or well-differentiated liposarcoma with myxoid change).[2, 3]

Potentially curative treatment is wide and complete surgical excision. If surrounding structures are unfavorable (neurovascular axis involvement), neoadjuvant chemotherapy andor radiotherapy can be considered to reduce tumour size. Ten percent of the cases are multicentric (contralateral limb or retroperitoneum). Distant metastasis usually appear in the first 2 years but are described 10 years later. Most common sites are retroperitoneum, soft tissue, skin and bone, and not the lung, contrarily to other sarcomas.[1, 2]
Factors associated with worse prognosis: greater proportion of round cell component, patient age greater than 45 years and the histologic presence of spontaneous necrosis. The overall 5-year survival rate for patients with myxoid liposarcoma ranges from 47% to 77%.[2]

- Myxoid liposarcoma has typical MRI characteristics that enable the Radiologist to make a very probable diagnosis based on imaging.
- Imaging findings can be used to direct biopsy of representative regions from both the lipomatous and non-lipomatous components and lead to improved pathologic evaluation.

Written informed patient consent for publication has been obtained.