Diagnostic and management challenges for MDM2-, CDK4-negative fatty tumors of the retroperitoneum

Abstract

Background: Neoplasms of the retroperitoneum that contain a major fat component may represent either benign entities, such as lipomas or angiomyolipomas, or malignancy such as liposarcoma. Distinguishing these diagnoses has important implications for management. While liposarcomas often stain positively for MDM2 and CDK4 proteins, absence of these markers can lead to diagnostic and management challenges.

Methods: We examined three cases in our institution of fat-containing masses of the retroperitoneum that lacked MDM2 and CDK4 markers to highlight the challenges in diagnosing and managing these cases. A thorough review of the literature examining radiologic and histologic features that can be used to determine that diagnosis was conducted and summarized.

Results: The three cases we present represent the three main diagnostic entities that can be found in among fatty tumors of the retroperitoneum: lipoma, angiomyolipoma, and liposarcoma. While radiologic features and analysis of histology helped to inform management, these cases in conjunction with the literature also illustrate the limitations of the diagnostic work up and importance also factoring the biologic behavior of the tumor in its management.

Conclusion: Fat-containing tumors of the retroperitoneum that do not stain for MDM2 or CDK4 can pose a diagnostic challenge. Assessing radiologic and pathologic features in conjunction with the biologic behavior of these tumors should inform their management.

Keywords: Angiomyolipoma; CDK4; MDM2; Retroperitoneal fatty tumor; Well-differentiated liposarcoma.

Fig. 1

CT scan from Case 1 demonstrates a tumor in the right retroperitoneum, most consistent with well-differentiated liposarcoma. a Transverse view shows that tumor is consistent with fat-density. b Coronal image demonstrates apposition to the right kidney without definitive invasion or “claw sign”, suggestive of renal angiomyolipoma

Fig. 2

H&E-stained histologic sections of the mass from Case 1. a The lesion is composed of well-differentiated adipose tissue with scattered, irregularly thickened vessels. There is no significant fibroconnective tissue, spindle cell proliferation or cytologic atypia. Scattered, thickened vessels are present. b Immunohistochemistry for HMB45 highlights scattered cells exhibiting strong, granular immunostaining

Fig. 3

CT scan from Case 2. a The coronal image demonstrates a large fatty mass located in the left retroperitoneum that appears to be exerting mass effect on adjacent structures without definitive signs of invasion. The mass is fairly homogenous in appearance. b Second attempt at CT-guided biopsy demonstrates good sampling centered within the mass

Fig. 4

H&E-stained sections of the mass from Case 2. a Histology demonstrates a well-circumscribed lesion with a thin fibrous capsule and smooth mesothelial-lined surface. b Higher power shows uniform, mature-appearing adipose tissue without cytologic atypia or increased spindle cells/loose fibroconnective tissue. There are normal-appearing, evenly distributed vessels and capillaries

Fig. 5

CT scan from Case 3. a Transverse image shows a large fatty tumor containing internal calcifications completely enveloping the left kidney, displacing the bowel, and crossing midline. b Coronal images demonstrate the extent of tumor involvement of the kidney, bowel, spleen, and great vessels across the midline. c Transverse view demonstrates a region of ill-defined soft-tissue density within the inferior portion of the mass

Fig. 6

H&E-stained section from Case 3 showing adipose tissue with variability in adipocyte size, myxoid stroma with loose fibroconnective tissue bands, and scattered atypical spindled cells exhibiting enlarged, hyperchromatic nuclei. Occasional lipoblasts identified (arrow)