liposarcoma

Liposarcomas are malignant tumors of fatty tissue and are the malignant counterpart to a benign lipoma. They are the second most common type of soft-tissue sarcoma.

Epidemiology

Liposarcomas are typically found in adults, typically between the ages of 40 and 60, and are rare in children.

Clinical presentation

It varies accordingly to the tumor location, usually related to a mass when involving the subcutaneous and extremities, and a vague discomfort when intra-abdominal or intrathoracic.

Pathology

Thought to originate from mesenchymal cells, they are classified histologically into five types :

  • ​well differentiated liposarcoma,
    • also known as atypical lipomatous tumor
    • most common (~50%) 
    • has the highest amount of fat content
  • myxoid liposarcoma / round cell
    • second most common
    • intermediate grade (myxoid) or high grade (round cell)
    • balanced chromosomal translocation t(12,16)
  • dedifferentiated liposarcoma
    • high grade, aggressive with frequent metastases
  • pleomorphic liposarcoma
    • least common
    • high grade, aggressive with frequent metastases
  • mixed
    • mixed liposarcoma
Location

They are usually seen in the extremities (75%), most commonly the thigh, and are less commonly seen in the retroperitoneum, groin or elsewhere (see:retroperitoneal liposarcoma).

Radiographic features

CT

Liposarcomas have three CT patterns based on the amount and distribution of fat in the tumor:

  • solid: attenuation over +20 HU
  • mixed: areas of less than -20 HU and areas of over +20 HU
  • pseudocystic: homogeneous density between –20 and +20 HU

CT findings favoring a liposarcoma over a lipoma include:

  • inhomogeneous attenuation, with evidence of significant amounts of soft-tissue within the fatty mass
  • poor definition of adjacent structures
  • evidence of infiltration or invasion of mediastinal structures
  • calcification
MRI

MRI appearance, as with CT, varies depending on the grade and amount of fatty tissue.

Low-grade lesions (atypical lipomas) are almost entirely fat signal with however thick septa, enhancement or evidence of local invasion. These features are used to distinguish these from simple lipomas .

The higher grade lesions are often devoid of macroscopic fat and have appearances similar to other sarcomas.

Treatment and prognosis

Both treatment and prognosis vary with location and grade.

Extremity liposarcomas, especially when well differentiated (atypical lipoma or atypical intramuscular lipoma) are indolent but nonetheless have a tendency to locally recur (0-69% of the time ). The rate of recurrence is higher for deep lesions compared to superficial ones.

High-grade lesions, especially those of the retroperitoneum, have a poor prognosis, with a recurrence rate of ~75% (range 63-91%) .

Surgical treatment is with wide local excision, which accounts at least in part for the more favorable outcome for extremity lesions.

Differential diagnosis

General imaging differential considerations include: