MR imaging of lipoma and liposarcoma

Purpose: To evaluate whether lipoma, atypical lipomatous tumors, and liposa rcomas can be differentiated by MR images. Material and Methods: The MR images of 59 lipomatous lesions and liposarcom as were retrospectively reviewed. Apart from size, surgical site, location and margins, the percentage of fat of the tumor volume was assessed as none , 1-75%, 75-95%, or 95-100%. Results: None of the 18 liposarcomas contained fat that could be recognized by MR imaging. The 3 atypical lipomatous tumors all contained fat but less than 75% of the tumor volume. In 32 of 38 ordinary lipomas, the percentage of fat was 95-100%, and in 4 less than 95% of the tumor volume. Two lipoma s did not contain fat that could be recognized by MR imaging. Conclusion. A lesion which predominantly has a fat signal is, in all probab ility, an ordinary lipoma. Lesions with less fat, but still mostly fatty, m ay either be lipoma or atypical lipomatous tumor. In this group, the discri mination between these two entities cannot be based upon imaging features. In the absence of a fat signal, liposarcoma or lipoma cannot be differentia ted from other soft tissue tumors.