Large retroperitoneal atypical spindle cell lipomatous tumor, an extremely rare neoplasm: A case report

Figure 1 Abdominal computed tomographic findings and gross findings. A: Large fatty mass with a complex soft tissue component. The tumor was filled the entire abdominal cavity and pushed up the abdominal viscera from the pelvic cavity; B: The tumor weigh approximately 5000 g, had an egg-shaped appearance, and mesures 38 cm × 24 cm × 11.5 cm in size; C: The cut surface show a large fatty mass with diffuse heterogeneous fibrotic change. No hemorrhage or necrosis is observed.

Figure 2 Microscopic findings. A: The neoplasm shows spindle cells with mild nuclear atypia and hyperchromatia. There are admixed adipocytes (Hematoxylin and eosin stain, × 100); B: The variation of adipocytic size and myxoid stroma are present (Hematoxylin and eosin stain, × 100); C: The spindle cells are negative for MDM2 (Immunohistochemical stain, × 200); D: Fluorescence in situ hybridization shows no MDM2 amplification.

Figure 3 Computed tomography. A: Pre-operative computed tomography findings; B: post-operative follow up computed tomography findings. At the 12-mo follow-up, no evidence of recurrence or metastasis was observed.