Soft tissue liposarcoma: histological subtypes, MRI and CT findings.

PURPOSE: Liposarcoma is the second most common malignancy of soft tissues. The commonly accepted classification of liposarcoma includes five basic histological categories: well-differentiated, myxoid, round cell, dedifferentiated and pleomorphic liposarcoma. The clinical behaviour of liposarcoma closely reflects its histological appearance, so that to identify the histological subtypes is very important for both prognosis and therapy. The aim of this study was to ascertain whether the histological features of liposarcoma subtypes can be correlated with MRI (Magnetic Resonance Imaging) and CT (Computed Tomography) findings by retrospectively evaluating nineteen cases of histologically-proved liposarcoma.
MATERIALS AND METHODS: The MRI examinations performed over the past eight years on nineteen patients affected by liposarcoma were retrospectively reviewed. All patients underwent ultrasound and MRI examination; T2 and T1-weighted sequences were available in all cases and fat-saturated sequences in 4 cases; all patients were administered paramagnetic contrast material. CT scans were obtained in twelve patients. All patients had a biopsy, surgical resection and histology.
RESULTS: The study group had 7 well-differentiated, 8 myxoid, 3 pleomorphic and 1 round cell liposarcoma. Well-differentiated liposarcomas had largely lipomatous appearance on both CT and MRI, typically with septa and areas showing high signal intensity on T2w MR images and low signal intensity on T1w images, and slightly hypodense compared to the muscle in CT, representing the sarcomatous areas. Myxoid liposarcomas were mildly heterogeneous with typical high signal intensity on T2w images and isointense to the muscle in T1w images, with lacy or linear septa of fatty tissue in six cases. The pleomorphic and round-cell subtypes demonstrated marked heterogeneity on MR images, with areas of necrosis and heterogeneous contrast enhancement, indistinguishable from other high-grade sarcomas. DISCUSSION AND
CONCLUSIONS: Well-differentiated liposarcoma may be distinguished from other types of liposarcoma by its largely lipomatous appearance. Myxoid liposarcoma may be distinguished on the basis of its homogeneous or mildly heterogeneous structure due to the large amounts of the extracellular myxoid material that give it its typical MR appearance. Both well-differentiated and myxoid liposarcomas, the most common types accounting for about 50% of all liposarcomas, have a more favourable clinical behaviour than the other histological types. Differentiation of these from the other histological types of liposarcoma therefore has a high significance for prognosis and therapeutical approach. On the basis of our experience and of the literature, we believe that diagnostic imaging and in particular the MR examination may lead to a correct diagnosis.