Atypical lipomatous tumor: Retrospective analysis, prognostic factors and MRI in differential diagnosis

Background: Atypical lipomatous tumor (ALT) is a locally aggressive soft tissue neoplasm with the tendency to local recurrence with no metastatic potential. The same tumor is defined as ALT when arises in the extremities and Well Differentiated Liposarcoma when located in the retroperitoneum or mediastinum. In both cases, there is the chance of dedifferentiation with malignancy progression increasing metastatic potential. Methods: Authors analyzed retrospectively 98 ALT / WDL treated in a single institution, 96% of which localized at the extremities and 4% at the trunk, assessing MRI characters (size, presence of septae, contrast enhancement), surgical treatment, local recurrence, follow-up and dedifferentiation ability. Surgical margins at final histology were classified in wide/radical, marginal and intralesional. Results: The most common location was the lower limb in 84% of cases, 52% showed sizes larger than 10 cm and 80% were deeply seated. MRI revealed thick septa in 83% and contrast enhancement in 78% of the cases. Eleven local recurrences of the disease (11%) have been observed. Only surgical margins represented a significant prognostic factor for local recurrence (p = 0.0007). No dedifferentiation or progression of malignancy in local recurrences was observed. Conclusions: The slow growth and the dedifferentiation ability in ALT/WDL needs a long follow up. MRI is the imaging method of choice.