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      Fatty tumors of the retroperitoneum: Lipoma or well-differentiated liposarcoma. About a case of a giant retroperitoneal liposarcoma


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          Introduction Fatty tumors of the retroperitoneum are rare and represent a real dilemma for urologist. Distinguishing between liposarcoma whish is a poor prognosis tumor and lipoma which is a benign tumor is sometimes difficult. We report the case of a 26 year-old, women presenting a giant fatty retroperitoneal mass measuring 17 × 10 cm. Through this case we report the management of the patient and we discuss diagnostic difficulties and treatment. Case A 26- year-old woman was referred to our center with a giant retroperitoneal mass. The patient complained about abdominal swelling and recurrent episodes of abdominal pain. Computed Tomography (CT) scan of the abdomen and pelvis showed a mass arising in the retroperitoneum. It was a homogenous hypodense mass surrounded by a thin capsule, well limited, measuring 10 × 8 × 17 cm and containing few thin septa. This mass was diagnosed as a lipoma by radiologist (Fig. 1A). The mass was in contact with the inferior vena cava, under the right kidney which was compressed on the posterior abdominal wall and represses the peritoneal containing to the left part of abdomen (Fig. 1B). No significant contrast enhancement was detected. We considered the mass resectable however very close to the right kidney. An open biopsy and intraoperative judgment helped the decision of complete resection of the tumor rather than en-bloc removal of the mass and right kidney. Fig. 1 A: Contrast enhanced CT scan in the axial plane showing a giant homogenous mass, mainly consisting of fat tissue surrounded by a thin capsule arising in the retroperitoneum pushing the right kidney to the posterior wall (*). B: Contrast enhanced CT scan in the coronal plane showing a 17 cm retroperitoneal mass repressing organs to the left and lower part of the abdomen. Fig. 1 The patient was operated through a Kocher incision. We found a giant clearly encapsulated fatty tumor deriving from the right retroperitoneal fatty tissue. An open biopsy of 3 cm in size was performed. Frozen section examination concluded to a retroperitoneal adipocytic tumor without cytologic atypia. The mass was completely extirpated without resection of adjacent tissue or organs. The patient was discharged on the fourth postoperative day without complications. The final histopathological report showed a well-differentiated liposarcoma of the retroperitoneum with mature adipocytic proliferation and presence of atypical, hyperchromatic stromal cells with lipoblasts (Fig. 2A and B). At 1 year post-surgery, there was no evidence of recurrence on different CT scans (Fig. 3). Fig. 2 A: Histological examination showed a mature adipocytic proliferation with variation in cell size. (Hematoxylin-Eosin, x 20). B: Histological examination showed presence of atypical, hyperchromatic stromal cells with a varying number of lipoblasts. (Hematoxylin-Eosin, x 40). Fig. 2 Fig. 3 Contrast enhanced CT scan in the axial plane after 1 year of follow up, showing no signs of recurrence. Fig. 3 Discussion Liposarcomas represent the most common type of sarcoma arising in the retroperitoneum. The rarity of retroperitoneal liposarcomas and the variety of histologic subtypes make it difficult to understand and treat this neoplasm. 1 The distinction between lipoma and well-differentiated liposarcoma is a frequent diagnostic dilemma. Computed tomography (CT) imaging features that suggest malignancy include large lesion size, presence of thick septa, presence of nodular and/or globular or non adipose masslike areas, and decreased percentage of fat composition. 2 Histopathology is fundamental for the diagnostic workup of lipomatous tumors. It can show fibrillar fibrous septa containing enlarged hyperchromatic cells and rare lipoblasts. However, there are some lipoma-like well differentiated liposarcoma that may be extremely difficult to distinguish confidently from lipoma due to their extreme paucity of hyperchromatic cells and lipoblasts. 3 In that case an immunohistochemical panel composed of MDM2 and CDK4 is recommended. Fluorescence in situ hybridization (FISH) for MDM2 amplification can be useful to discriminate lipomas from atypical lipomatous tumor and well-differentiated Liposarcomas. 4 In our case, MDM2 and CDK4 are unfortunately unavailable. Surgery is the mainstay of treatment of non-metastatic retroperitoneal lipomatous tumors. Whenever is possible, a macroscopically complete resection should be aimed at, often requiring en-bloc removal of adjacent structures. 5 In case of unresectability or patients with hematogenous metastases a biopsy should be reserved. Tissue may be obtained through fine-needle aspiration or core-needle biopsy. Percutaneous biopsies are reliable and safe. However, percutaneous techniques have a low subtype specific diagnostic in liposarcoma. In our case, CT scan images and frozen section examination concluded to a retroperitoneal lipoma however final histological examination showed presence of atypical, hyperchromatic stromal cells confirming the diagnosis of well-differentiated liposarcoma. The current guidelines from the National Comprehensive Cancer Network for the surveillance of retroperitoneal sarcomas recommend that patients with low-grade tumors who have been successfully resected should have a follow-up physical examination with imaging (chest/abdominal/pelvic CT) every 3–6 months for 2–3 years, then annually. Conclusion The distinction of lipoma-like well-differentiated liposarcoma from lipoma is difficult. The large lesion size, presence of thick septa, presence of nodular areas on CT scan, intraoperative judgment and mature adipose tissue on histology could make the diagnosis. Molecular testing could be useful in the differential diagnosis of lipomatous tumors. The resection should be complete with a strict follow up. Conflicts of interest None for all authors. Funding This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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          Well-differentiated liposarcoma. The Mayo Clinic experience with 58 cases.

          The clinicopathologic results from 58 patients with well-differentiated liposarcomas are reported. Thirty-two tumors involved the extremities, 20 the retroperitoneum, 4 the scrotum, 1 the abdominal wall, and 1 the cheek. Most tumors were large (mean, 22.6 cm). There were 31 (53%) lipoma-like, 23 (40%) sclerosing, and 4 (7%) primary dedifferentiated tumors. Six tumors underwent dedifferentiation after recurrence. The average follow-up period was 9.3 years. Thirty-seven patients (64%) were alive with no evidence of disease; 7 (12%) were alive with disease; 8 (14%) died of disease; and 6 (10%) died of other causes. Dedifferentiation did not indicate imminent death; 5 of the 10 patients were alive with no evidence of disease. Three dedifferentiated tumors subsequently recurred as pure well-differentiated liposarcomas. Patients with extremity tumors had a significantly better prognosis than those with retroperitoneal or scrotal tumors (P = .006). Extremity tumors treated by wide local excision recurred in only 11% of cases, whereas 60% of those treated by marginal or simple excision recurred.
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            MDM2 Amplification in Problematic Lipomatous Tumors: Analysis of FISH Testing Criteria.

            To discriminate lipomas from atypical lipomatous tumor/well-differentiated liposarcoma (ALT/WDL) we perform fluorescence in situ hybridization (FISH) for MDM2 amplification in several problematic situations: "lipomas" >10 cm, lesions with equivocal atypia, recurrent "lipomas," all retroperitoneal/pelvic/abdominal "lipomas", and in cases not fitting the above criteria but having worrisome clinical or radiologic features. To ascertain the validity of these criteria, we have reviewed our experience with 301 consecutive differentiated lipomatous tumors in which the diagnosis of ALT could not be established on the basis of histologic sections and in which FISH was performed on the basis of the above criteria. The final diagnosis was based on MDM2 amplification status. Given the nature of this study to evaluate difficult lesions, most cases included (74%) were received in consultation. This enhanced our study series for borderline cases, and the data presented may not be generalizable to adipocytic tumors seen outside a subspecialty setting. Of 301 cases, 108 proved to be ALT/WDL (36%). The most common test indication was size >10 cm (n=187), followed by equivocal atypia (n=145), retroperitoneal/pelvic/abdominal location (n=86), recurrence (n=33), and clinical concern (n=12). Of the tumors >10 cm, 68 (36%) proved to be ALT/WDL, whereas the remainder were interpreted as lipoma or its variants (eg, spindle cell or pleomorphic lipoma). The 2 groups did not differ statistically in size, although ALTs consistently occurred in patients above 50 years of age. Of the cases with equivocal atypia, 72 (50%) proved to be ALT/WDL. Those in the retroperitoneum/abdomen/pelvis were ALT/WDL in 30 cases (35%), and those that had recurred were ALT in 18 cases (55%). Recurrence, atypia, and having multiple indications for testing were more common in ALT than in benign lesions (P=0.02, 0.0001, 0.0012, respectively). No ALT/WDL occurred in the hands and feet, and only a single ALT/WDL was superficial (1 ALT/WDL vs. 60 lipoma/spindle cell or pleomorphic lipoma). Small ( 10 cm in patients over 50 years of age; (3) in cases with equivocal atypia; (4) in lesions of the retroperitoneum/pelvis/abdomen, and in special clinical situations as directed by treating clinicians. Testing is low yield in superficial lesions, in small extremity lesions without additional indicators for testing, in large extremity lesions without additional features in patients under the age of 50, and in lesions arising in the hands/feet. More evidence is needed regarding testing in small retroperitoneal lesions without additional features. By adopting these criteria, we could have avoided testing 74 cases, missing a single superficial ALT/WDL.
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              Retroperitoneal lipomatous tumors without cytologic atypia: are they lipomas? A clinicopathologic and molecular study of 19 cases.

              Most well-differentiated liposarcomas can be readily distinguished from lipomas on histologic grounds alone. However, occasional retroperitoneal lipomatous tumors show no cytologic atypia. To determine whether these tumors are well-differentiated liposarcomas devoid of cytologic atypia or lipomas was the major aim of this investigation. We comprehensively and prospectively studied 19 retroperitoneal adipocytic tumors devoid of cytologic atypia at the cytogenetic and molecular genetic levels. Median patient age was 56 years (range: 36 to 78 y). Median tumor size was 21 cm (range: 8 to 46 cm) and the median weight was 1127 g (range: 173 to 2440 g). All tumors were well-circumscribed and showed no cytologic atypia. Standard cytogenetic analysis demonstrated rearrangements of 12q15 in 4 (of 7) cases. None showed ring or giant marker chromosomes. Fluorescence in situ hybridization failed to identify amplification of MDM2, carboxypeptidase M(CPM), SAS, CDK4, DDIT3, or HMGA2 in all cases. HMGA2 rearrangement was observed in 8 (of 19) cases (42%) and was more common in larger tumors (P=0.046). HMGA2-LPP fusion was seen in only 1 case. All tumors were completely excised. Follow-up information was available from 10 cases (median, 6 mo; range: 1 to 58 mo). No tumor recurred or metastasized. In contrast, a control group of 20 well-differentiated liposarcomas diagnosed during the same time period (matched per year of diagnosis) showed 4 instances of local recurrence. We conclude that this group of retroperitoneal lipomatous tumors shows clinico-pathologic and genetic features more akin to lipomas than well-differentiated liposarcomas. Owing to their apparent rarity, additional studies are necessary to more fully understand their natural biology in this anatomic location.

                Author and article information

                Urol Case Rep
                Urol Case Rep
                Urology Case Reports
                04 September 2018
                November 2018
                04 September 2018
                : 21
                : 58-60
                [a ]Department of Urology, La Rabta Hospital, Tunis, Tunisia
                [b ]Department of Pathology, La Rabta Hospital, Tunis, Tunisia
                [c ]Department of Radiology, La Rabta Hospital, Tunis, Tunisia
                Author notes
                []Corresponding author. dr.mokhtarbibi@ 123456gmail.com
                © 2018 Published by Elsevier Inc.

                This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).


                lipoma,liposarcoma,retroperitoneal tumor
                lipoma, liposarcoma, retroperitoneal tumor


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