Purpose of the study: The prognosis of subfascial lipomatous soft tissue tumors depends greatly on their histological type ranging from benign lipomas that cause little local or general problems to the severe prognosis of liposarcomas that exhibit both local and distant extension. However, the clinical presentation of the two types of tumors may be similar and thus quite misleading, sometimes leading to inappropriate management and severe consequences. The main objective of this study was to determine whether the preoperative work-up in patients treated for musculoskeletal tumors within our recruitment zone is adequate, allowing appropriate therapeutic decisions. In addition, we wanted to know what explorations are most pertinent for the differential diagnosis between benign and malignant subfascial lipomatous soft tissue tumors.
Material and methods: Thirty-seven patients with subfascial tumors were included in this study. There were 16 with benign lipomas and 21 with liposarcomas. All the patients with benign lipomas but only 9 (43%) of those with liposarcoma had received initial care within our recruitment zone before final diagnosis. Two cases had been referred after biopsy and 1 after resection by morcellation; the 9 others were secondary referrals after tumor recurrence. Only 5 of these 12 referred patients had had an MRI exploration prior to surgery, 2 with an erroneous interpretation. An MRI series was obtained for all the patients with benign lipoma and for the 9 with liposarcomas who attended our units directly. A biopsy was also obtained in case of suspected liposarcoma. Two radiologists blinded to the final diagnosis reviewed the available MRI to assess their diagnostic value for subfascial lipomatous soft tissue tumors.
Results: No case of recurrence, after marginal resection (10 cases) was noted for lipomas. Six are under observation with regular MRI (with no change in size or signal). Four patients with liposarcoma died from their disease (19%) and 2 who had undergone "curative" resection had a recurrence (12%). Incorrect or imprecise (incomplete, incorrectly interpreted or no MRI) preoperative diagnosis led to additional morbidity with 3.4 surgical procedures (mean per patient) compared with 1 in patients who had had undergone a complete work-up and whose diagnosis was established after multidisciplinary discussions. Among the diagnostic elements available before pathology, only MRI findings had diagnostic value for subfascial lipomatous soft tissue tumors: for benign lipoma positive predictive value=92% and negative predictive value=93%.
Discussion: The clinical course of the benign lipomas and the sarcomas in this series confirm the radically different prognosis of these two tumors, both in terms of local extension and survival. Inadequate management in the initial diagnostic stages-i.e. lack of MRI with contrast injection, biopsy and multidisciplinary interpretation prior to treatment-raises the risk of higher morbidity, particularly a significantly greater number of reoperations, and progression to a higher grade of malignancy for two tumors. Our retrospective analysis enabled us to develop a decision making tree for patients with subfascial lipomatous tumors. Prospective validation will be necessary.