18F-FDG PET/CT imaging features of lipomatous tumors.

The objective was to evaluate the 18F-FDG PET/CT characteristics of lipomatous tumors, and examine features helpful in differentiating benign from malignant tumor subtypes. Patients undergoing 18F-FDG PET/CT from 01/2005 to 03/2018 with subsequent pathologically confirmed liposarcoma, lipoma, or hibernoma were retrospectively reviewed with IRB approval. A variety of imaging features, including metabolic activity and tumor morphology were noted. 67 tumors were included: 13 lipomas, five hibernomas, 16 atypical lipomatous tumors, 16 dedifferentiated liposarcomas, 15 myxoid liposarcomas, and two pleomorphic liposarcomas. There were 42 males and 23 females, mean age 58.8 ± 13.6 years. Mean SUVmax of lipomas measured 0.8 ± 0.2, atypical lipomatous tumors 2.3 ± 1.2, myxoid liposarcomas 3.0 ± 1.0, hibernomas 11.9 ± 8.4, pleomorphic liposarcomas 13.5 ± 2.9, and dedifferentiated liposarcomas 16.3 ± 11.4. There was no significant difference in metabolism between benign and malignant subtypes (SUVmax 3.9 ± 6.5 versus 7.6 ± 9.2, P = 0.13). There was a significant difference in metabolism between low- and high-grade liposarcoma (SUVmax 2.5 ± 1.2 versus 12.8 ± 10.8, P = 0.0001). 10/13 lipomas, 2/5 hibernomas, and 2/16 atypical lipomatous tumors had no internal soft tissue content. There are overlapping 18FDG PET/CT features of benign and malignant lipomatous tumors. While liposarcoma grade correlates with SUVmax, malignant lesions (myxoid liposarcomas and atypical lipomatous tumors) may present with low FDG uptake and benign lesions (hibernomas) may demonstrate high metabolic activity. In some instances, a combination of metabolic and morphologic characteristics may narrow the differential diagnosis, or even be diagnostic.