Liposarcoma is a malignant soft tissue tumor arising from adipose tissue and is one of the most common soft tissue sarcomas in adults. It accounts for 20-25% of all soft tissue sarcomas. It is most common between ages 50-70 with a slight male predominance. Lower extremity (thigh) and retroperitoneum are the most common locations. According to WHO 2020 classification, there are four main subtypes: well-differentiated (atypical lipomatous tumor/ALT), dedifferentiated, myxoid, and pleomorphic. Prognosis and imaging features differ significantly depending on the subtype.
Age Range
40-70
Peak Age
55
Gender
Male predominant
Prevalence
Uncommon
Liposarcomas are malignant adipose neoplasms arising from mesenchymal stem cells. Well-differentiated liposarcoma (ALT) resembles mature fat cells but contains nuclear atypia and thickened fibrous septae; MDM2 and CDK4 gene amplification (chromosome 12q13-15) is characteristic and used as a diagnostic FISH/IHC test. This genetic alteration translates on imaging as thickened septae and non-adipose nodular components within a background of lipoma-like fat signal. Dedifferentiated type represents development of non-lipomatous high-grade sarcoma within a well-differentiated background; it appears on MRI as a solid mass without fat signal. Myxoid liposarcoma carries the DDIT3-FUS fusion gene and contains abundant myxoid matrix; this myxoid stroma produces very bright T2 signal and slow progressive enhancement. Pleomorphic type is the most aggressive form with minimal fat component, appearing as a heterogeneous necrotic mass. Subtype identification directly affects treatment planning: ALT shows local recurrence but does not metastasize; dedifferentiated and pleomorphic types carry metastatic potential.
Heterogeneous suppression pattern on fat-suppressed sequences — while fat components are suppressed, thick septae, nodular areas and solid components remain bright. This pattern distinguishes from lipoma showing homogeneous complete suppression and raises suspicion for liposarcoma.
In well-differentiated liposarcoma, most of the mass is fat signal (hyperintense) on T1 but thickened septae and nodular non-adipose components appear T1 hypointense. In dedifferentiated type, a T1 hypointense solid mass is seen within a lipomatous background. In myxoid type, T1 intermediate-to-low signal with minimal fat. In pleomorphic type, heterogeneous T1 signal with possible T1 hyperintensity in hemorrhagic areas.
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On T1-weighted sequences, non-adipose hypointense components (thick septae/nodular areas) are seen within a predominantly fatty mass, consistent with well-differentiated liposarcoma.
On T2, liposarcoma shows different patterns depending on subtype. Well-differentiated: fat signal + intermediate signal between septae. Dedifferentiated: solid component heterogeneous intermediate-to-high signal. Myxoid: very marked T2 hyperintensity (myxoid matrix gives water-like signal), nearly cyst-like high signal. Pleomorphic: heterogeneous, necrotic areas high signal.
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On T2-weighted sequences, the mass demonstrates heterogeneous signal characteristics with non-adipose components within a fatty background, consistent with liposarcoma.
On STIR sequences, liposarcoma shows heterogeneous signal. While fat components are suppressed, non-adipose components (thick septae, nodular areas, myxoid stroma) remain bright. Unlike lipoma, complete and homogeneous suppression is not seen. This incomplete suppression pattern is the most valuable STIR finding in liposarcoma diagnosis.
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On STIR sequences, heterogeneous signal is seen within the mass with residual hyperintense non-adipose components despite fat suppression, consistent with liposarcoma.
On post-contrast fat-suppressed sequences, non-adipose components (thick septae, nodular areas, solid mass) show enhancement. Septal enhancement in well-differentiated type, avid enhancement of solid component in dedifferentiated type, slow progressive enhancement in myxoid type are characteristic. Fat component shows no enhancement.
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On post-contrast fat-suppressed sequences, enhancement of non-adipose components is seen, consistent with liposarcoma.
On CT, well-differentiated liposarcoma shows predominantly fat-density (negative HU) mass with thickened septae and nodular components at soft tissue density. In dedifferentiated type, a solid mass at soft tissue density is adjacent to/within a fat-density area. In myxoid type, minimal fat density with a mass near water density. Calcification is rare.
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On CT, non-adipose components at soft tissue density are seen within a predominantly fat-density mass, consistent with liposarcoma.
On DWI, solid/dedifferentiated components of liposarcoma may show diffusion restriction (high DWI signal + low ADC). Fat components are suppressed on DWI. Myxoid liposarcoma may appear bright on DWI due to T2 shine-through but ADC values are high (no true restriction). ADC values may reflect tumor grade; low ADC suggests more aggressive subtype.
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On DWI, diffusion restriction is seen in the solid components of the mass, consistent with dedifferentiated/aggressive component.
On PET-CT, FDG uptake varies by subtype. Well-differentiated: low-moderate FDG (SUVmax usually <4). Dedifferentiated: avid FDG uptake (SUVmax >4-5, usually >8). Myxoid: low FDG (may be false negative). Pleomorphic: high FDG. PET-CT is valuable for detecting dedifferentiated component and staging.
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On PET-CT, increased FDG uptake is seen in the solid components of the mass, consistent with dedifferentiated/high-grade component.
Criteria
Predominantly fat component + thick septae (>2mm) + non-adipose nodular component, MDM2/CDK4 amplification positive
Distinct Features
Most common subtype (40-45%). High local recurrence rate but does not metastasize. In extremity location, the term 'ALT' is used (low grade). Retroperitoneal location requires aggressive management due to 15-20% risk of dedifferentiation and surgical difficulty.
Criteria
Non-lipomatous high-grade solid component within well-differentiated background ('collision' pattern), abrupt transition, MDM2/CDK4 amplification positive
Distinct Features
Has metastatic potential (15-20%). On MRI, sharp transition between fat-signal area and solid mass. Solid component resembles UPS/pleomorphic sarcoma. Retroperitoneal location most common. On PET-CT, dedifferentiated component shows avid FDG uptake.
Criteria
DDIT3-FUS fusion gene positive, abundant myxoid matrix, very bright T2 signal (water-like), slow progressive enhancement, minimal mature fat
Distinct Features
More common in young adults (30-50 years). Lower extremity (thigh) most common location. Very bright T2 signal may be confused with cyst but shows enhancement. Can metastasize to bone and soft tissue (extrapulmonary metastasis common — bone, contralateral extremity, retroperitoneum). Increased round cell component indicates worse prognosis.
Criteria
High-grade pleomorphic cells, minimal or absent fat component, areas of necrosis and hemorrhage, aggressive behavior
Distinct Features
Rarest (5%) and most aggressive subtype. Minimal fat component may make it indistinguishable from other high-grade sarcomas on imaging. Diagnosis is made histopathologically by identifying lipoblasts. High metastasis rate (30-50%). Poor prognosis. More common in older adults.
Distinguishing Feature
In lipoma, the entire mass follows homogeneous fat signal, complete and homogeneous suppression on fat-suppressed sequences, septae <2mm and thin, no enhancement; in liposarcoma, thick septae >2mm, non-adipose nodular component, and enhancement present
Distinguishing Feature
Soft tissue sarcoma (UPS) contains no fat component, entirely solid heterogeneous mass; liposarcoma (in well-differentiated and dedifferentiated types) contains fat component. Pleomorphic liposarcoma may be indistinguishable from UPS on imaging
Distinguishing Feature
Schwannoma is nerve-related, shows split-fat sign (fat surrounds mass but no fat signal within mass), target sign; liposarcoma has no nerve association and contains fat signal within the mass
Distinguishing Feature
Hemangioma in typical location (vertebral body), polka dot/corduroy pattern, simultaneous T1 and T2 hyperintensity; liposarcoma soft tissue location, no trabecular pattern, heterogeneous
Urgency
semi-urgentManagement
wide surgical excision; MDM2/CDK4 testing for definitive subtyping; multidisciplinary tumor boardBiopsy
NeededFollow-up
regular MRI follow-up post-resection (every 3-6 months for 2-3 years, then annually); PET-CT for dedifferentiated/pleomorphic types; monitor for dedifferentiation in recurrent ALTLiposarcoma subtype determines treatment approach. Well-differentiated type (ALT) requires wide surgical resection; does not metastasize but local recurrence is common. Dedifferentiated type may require surgery + adjuvant therapy; carries metastatic risk. Myxoid type is sensitive to chemotherapy and radiotherapy. Pleomorphic type is most aggressive and requires multimodal treatment. Biopsy is mandatory and MDM2/CDK4 FISH/IHC testing is the gold standard for subtyping and differential diagnosis from lipoma. MRI and biopsy are recommended for all deep-seated, >5cm, or lipomatous masses with atypical features for lipoma.
Treatment is wide surgical excision. Well-differentiated type has the lowest aggressiveness, while dedifferentiated and pleomorphic types are high-grade aggressive tumors. Retroperitoneal liposarcomas often reach giant sizes with high local recurrence rates. MRI is essential for staging and surgical planning.