Imaging Features of Atypical Lipomatous Tumor/Well-differentiated Liposarcoma and the Significance of This Lesion Dependent on Location

Purpose or Learning Objective: To review the imaging features of atypical lipomatous tumor/well-differentiated liposarcoma and the significance of this lesion with a focus on its location.

Methods or Background: Atypical lipomatous tumor and well-differentiated liposarcoma represent the same lesion with the term atypical lipomatous tumor used to describe lesions located in anatomical sites in which complete surgical resection is curative. The term well-differentiated liposarcoma is largely reserved for lesions arising in anatomical sites such as the retroperitoneum and mediastinum, where there is greater potential for recurrence and disease progression. Atypical lipomatous tumor/well-differentiated liposarcoma does not metastasize but has the potential to dedifferentiate into a dedifferentiated liposarcoma, highlighting the importance of recognizing these lesions.

Results or Findings: The main differential of these fatty lesions are simple lipomas. Imaging features that can help differentiate an atypical lipomatous tumor/well-differentiated liposarcoma from a simple lipoma are location, size, and the imaging characteristics of the lesion. Atypical lipomatous tumor/well-differentiated liposarcoma most commonly occurs in the retroperitoneum and the deep subfascial tissues of the extremities, such as the thigh, although it can also occur in the subcutaneous tissues, head/neck, and mediastinum. Atypical lipomatous tumor/well-differentiated liposarcoma tends to be larger than simple lipomas with a size > 10 cm often used as a discriminator. The presence of nodules, masses, and thickened septa all favor the diagnosis of an atypical lipomatous tumor/well-differentiated liposarcoma over a lipoma. The risk of dedifferentiation depends highly on the location of the lesion with those in the retroperitoneum most at risk. Conversely, dedifferentiation of a subcutaneous atypical lipomatous tumor is extremely rare.

Conclusion: The radiologist should be aware of the imaging features that suggest an atypical lipomatous tumor/well-differentiated liposarcoma, as opposed to a simple lipoma, to identify lesions in which biopsy or excision is necessary. The radiologist should also be aware of the variable natural history of these lesions depending on their location.

Publication History

Article published online:
02 June 2025