PMC3884005_01
Computed tomography (A) and magnetic resonance imaging findings (B and C) demonstrate an ovoid encapsulated retroperitoneal mass, which contained predominantly fat and a few solid hypervascularized nodules (arrows).
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F1
As an accidental finding, the contrast-enhanced CT scan additionally showed an 8 x 11 x 15 cm large retroperitoneal mass in the lower left abdomen adjacent to the sigmoid colon and the left psoas muscle (Figure 1A). Contrast-enhanced magnetic resonance imaging (MRI) confirmed the lesion to be composed predominantly of fat with a few solid hypervascularized nodules (Figure 1B and C).
Macroscopic appearance (A) and histology with H&E staining (B) and immunohistochemistry (IHC) for smooth muscle actin (C) and human melanoma black (HMB)-45 (D).
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F2
Macroscopic appearance as well as histology and immunohistochemistry of the mass are shown in Figure 2. Macroscopic evaluation of the surgical specimen confirmed the predominance of fat within the thinly encapsulated tumor (Figure 2A). Histology demonstrated the presence of large-sized lipid vacuoles and small, disseminated islands of lipoblasts (Figure 2B). Immunohistochemically, these cells showed only weak staining for melan-A, desmin and smooth muscle actin (SMA) (Figure 2C). S-100 staining was negative but strong reaction was found for human melanoma black HMB-45 (Figure 2D).