2nd most common soft tissue sarcoma (approximately 25%)
Histologically classified into well differentiated, dedifferentiated, myxoid, pleomorphic, mixed types.
Well differentiated liposarcoma (atypical lipoma):
Most common type of soft tissue liposarcoma (50%)
Almost exclusively in adults, common in 60-70 years
Most commonly seen in deep soft tissues (intramuscular, but also intermuscular or subcutaneous) of extremities (75%); 50% occur in lower limb, particularly thigh. 2nd most common site is retroperitoneum (1/3) and then upper limb (15%). Also seen in head and neck, trunk
Lack of metastatic potential; high local recurrence if deep seated
Present as painless slow-growing mass
Radiograph:
focal soft tissue swelling; calcifications/ossifications in 10-30%; underlying bone is usually normal
Ultrasound:
Heterogeneous multi-lobulated well defined mass; cannot differentiate from other lipomatous lesions
CT:
Predominantly fatty mass with some non-lipomatous components; usually more than 75% of mass is fat; thick septa of more than 2 mm; nodular septae; non-fat areas usually less than 2 cm
MR:
Predominantly fatty mass with some non-lipomatous components; usually more than 75% of mass is fat; thick septa of more than 2 mm; nodular septae; non-fat areas usually less than 2 cm; modearte to marked Gd enhancment
Differentiation from other lipomatous lesions:
Difficult to differentiate from lipoma: Usually lipomas contain fat only, thin septae of less than 2mm; no to moderate Gd enhancement. But lipomas may have complex appearance (1/3) mimicking well differentiated liposarcoma
Myxoid liposarcoma:
2nd most common type, represnting 20%–50% of liposarcomas
A decade younger than other liposarcomas (40-50 years)
Most common type of liposarcoma affecting children (75%)
Most commonly seen in intermuscular lesions (75%), lower limb (75%), especially medial thigh and popliteal area
Radiographs are often nonspecific, but calcification is less frequent
US:
Complex, well-defined, hypoechoic, noncystic mass with posterior enhancement. Fat is not usually seen.
Popliteal myxoid liposarcoma is common and may be mistaken for Baker cyst
CT:
Often pathognomonic appearance of large well defined lobulated intermuscular mass of fluid attenutaion with presence of adipose tissue
MR:
Often pathognomonic appearance of large well defined lobulated intermuscular mass of low signal T1 and high on T2 with presence of fat, which constitutes usually less than 10% of tumor size
Septa (lacy or linear) or small nodules may be seen
Enhance on Gd which helps to distinguish from a cystic lesion. The enhancement patterns include peripheral nodular, central nodular and diffuse
May simulate a cyst (10%), but atypical location for synovial cyst/ganglion, absent thick wall, absent surrounding edema suggest myxoid liposarcoma
Myxomas are usually intramuscular with muscle atrophy and edema
Treated with wide surgical resection, radiotherapy and chemo
Extrapulmonary metastasis are common
Dedifferentiated liposarcoma: (10% )
Composed of well differentiated liposarcoma and a nonlipomatous sarcoma
Common in 60-70 years
Most common in retroperitoneum (2/3); seen in Lower limb (1/4), upper limb; rare in subcutaneous tissue.
Risk of dedifferentiation: 15% for retroperitoneal tumors, 5% deep extremity lesions with average latent period of 7–8 (17–20) years
The two components often seen as distinct regions with abrupt transition. Usually the non-lipid compnent is high grade fibrosarcoma or MFH in 90% of cases
Treat with wide surgical excision, radiotherapy and may be with chemotherapy
40% recur
Metastasis in 10-20%, common in lung, liver, bone
Radiologically, dedifferentiation is suggested by non-lipomatous focal/nodular area of more than 1 cm. The appearance of non-lipomatous area depends on amount of myxoid and fibrous content CT:
Non-lipid area shows attenuation similar to adjacent muscle
MR:
Non-lipomatous areas show low-to- int signal on T1and int-to-high on T2. Gd MR may be useful for identifying fat necrosis, which shows thin peripheral rim enhancement (c.f. diffuse or peripheral nodular enhancement in dedifferentiation). The differential for non-fat area includes collagenized tissue, metaplastic mineralization, region of dedifferentiation, fat necrosis.
Pleomorphic liposarcoma:
Agressic high grade tumor
Least common type (10%)
usually 50-60 years
Most cmmonly in intramuscular location, lower limb (50%)
Radiographic appearance is nonspecific
US, CT, MR show relatively well defined mass with infiltrative margins
Necrosis and hemorrhage is common
Less frequently contain adipose tissue (75%)
Treated with surgery, chemo and radiotherapy
Mixed type liposarcoma:
10% of liposarcomas
Combination of other subtypes.
Older patients
Common sites are retroperitoneum and abdominal cavity
Liposarcoma of bone
References:
Murphey MD et al. Imaging of Musculoskeletal Liposarcoma with Radiologic-Pathologic Correlation . RadioGraphics 2005;25:1371-1395
