Well-Differentiated Liposarcoma, Atypical Lipomatous Tumor, and Friends

Atypical lipomatous tumor and well-differentiated liposarcoma refer to the exact same tumor (see below for more synonyms). They are intermediate-grade malignant neoplasms with a mature lipomatous proliferation that are locally aggressive, but which do not metastasize (unless they dedifferentiate).

The choice of terminology depends on the urgency the pathologist or radiologist wants to convey in the record, as well as the consensus between them and the surgeon in order to prevent either inadequate or excessive therapy.

This vagueness/flexibility is due to the fact that the location of this tumor make a big difference on the possibility of getting tumor-free margins, and consequently, a difference in local recurrence and prognosis.

For example, in the retroperitoneum, mediastinum, and the spermatic cord, getting a tumor-free margin is usually impossible, and, as a result, local recurrence is common and often fatal, with a mortality rate of 80%. The same tumor in the extremities is far more easily resected with clear margins, with a mortality rate of close to 0%.

For this reason, the use of the term well-differentiated liposarcoma conveys the correct level of urgency when the tumor is located in the retroperitoneum or mediastinum, while the term atypical lipomatous tumor is more suited for lesions in the extremities.

The WHO lists the following as old synonyms for atypical lipomatous tumor and well-differentiated liposarcoma:

• Atypical lipoma
• Adipocytic liposarcoma
• Lipoma-like liposarcoma
• Sclerosing liposarcoma
• Spindle cell liposarcoma
• Inflammatory liposarcoma

On MRI, atypical lipomatous tumors are fatty tumors that are differentiated from lipomas by the presence of thickened or nodular septa, associated nonadipose masses, prominent foci of high T2 signal, and prominent areas of enhancement (pink arrows).

References

• Gaskin CM, Helms CA. Lipomas, lipoma variants, and well-differentiated liposarcomas (atypical lipomas): results of MRI evaluations of 126 consecutive fatty masses. AJR Am J Roentgenol. 2004 Mar;182(3):733-9.
• Tos APD, Pedeutour F. Atypical lipomatous tumour / Well differentiated liposarcoma. in Pathology and Genetics of Tumours of Soft Tissue and Bone. Fletcher CDM, Unni KK, Mertens F (eds). IARCPress Lyon, 2002. pp 35-37.
• Weiss SW, Rao VK. Well-differentiated liposarcoma (atypical lipoma) of deep soft tissue of the extremities, retroperitoneum, and miscellaneous sites. A follow-up study of 92 cases with analysis of the incidence of "dedifferentiation". Am J Surg Pathol. 1992 Nov;16(11):1051-8.