Non-Radiographic Risk Factors Differentiating Atypical Lipomatous Tumors from Lipomas

Abstract

Purpose: To determine non-radiographic risk factors differentiating atypical lipomatous tumors (ALTs) from lipomas.

Methods: All patients with deep-seated lipomatous tumors of the extremities treated from January 2000 to October 2010 were retrospectively reviewed. Factors reviewed included age, gender, tumor location, size, histology, local recurrence, dedifferentiation, and metastasis. Multivariate logistic regression models were used to evaluate the effects of patient characteristics on ALT status.

Results: Ninety-four lipomas and 46 ALTs were included. Patients with an ALT were older (median: 60.5 vs. 55 years). Lipomas were evenly distributed between upper (48.9%) and lower extremities (51.1%), whereas ALTs predominately involved the lower extremities (91.3%). Median ALT size (22 cm) was greater than lipomas (10 cm), p < 0.0001. One lipoma (1.04%) recurred at 77 months and five ALTs (10.9%) recurred at an average of 39 months (19-64 months). Two ALTs originally treated with wide resection recurred with a dedifferentiated component and were treated with wide re-excision and chemotherapy. No metastases or tumor-related deaths occurred in either group at the time of last follow-up. Patients older than 60 years, tumors greater than 10 cm, or thigh location, were more likely to be diagnosed with an ALT (p < 0.05).

Conclusion: Lipomatous tumors were more likely to be ALTs when the tumor was at least 10 cm in size, located in the thigh, or found in patients that were 60 years of age or older. These risk factors may be used to guide management and surveillance strategies, when lipomatous tumors do not display characteristic radiographic features.

Keywords: atypical lipomatous tumor; lipoma; liposarcoma; well-differentiated liposarcoma.

Figure 1

Upon initial presentation, (A) coronal and (B) axial T1 MRI showed a large deep-seated lipomatous mass within the medial thigh. The majority of the mass is lipomatous with some septations consistent with an ALT, which was confirmed on histology. Seven years following resection, MRI now shows a heterogenous lesion within the same region with very little fat signal that is dark on T1 (C) with intermediate signal on T2 (D) and enhances with gadolinium contrast (E). (F) Needle biopsy shows scattered pleomorphic spindle cells confirming the diagnosis of dedifferentiated liposarcoma.