PMC9684626_01
Imaging findings. T1-weighted axial images showing low and slightly high signals (yellow asterisk) (A); almost homogeneous high signal on T2-weighted images (B) and short tau inversion recovery images (C); and axial and central enhancement on a gadolinium-enhanced T1-weighted axial image (D, E). Axial fluorodeoxyglucose (FDG) positron emission tomography-computed tomography (PET-CT) showing a hypometabolic tumor (F).
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MRI revealed a low-intensity signal on T1-weighted images with a few high-intensity signals that suggested the presence of intratumoral fat ( Figure 1A ). High signal intensity on T2-weighted images ( Figure 1B ) and T2 short tau inversion recovery images ( Figure 1C ) suggested the presence of myxoid components. Heterogeneous enhancement was noted on gadolinium-enhanced T1-weighted images ( Figures 1D, E ). Positron emission tomography-computed tomography (PET-CT) showed slight 18F-fluorodeoxyglucose uptake in the right buttock mass, with an SUVmax of 2.8 ( Figure 1F ).
Histological findings of the needle biopsy specimen. Pathological examination showed mild proliferation of spindle cells with few atypical cells in a myxoid background (A, x100 B, x200).
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However, needle biopsy findings suggested myxoma, because there were few atypical spindle cells ( Figures 2A, B ).
Intraoperative and pathological findings of the resection specimen. The tumor was located inside the gluteus maximus (A). Macroscopically, the tumor measured 16 x 15 x 12 cm in size (B). The tumor consisted of large myxoid components and small fatty components (yellow asterisk) (C).
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The tumor was located within the gluteus maximus ( Figure 3A ). Macroscopically, the tumor measured 16 x 15 x 12 cm in size and consisted of mainly myxoid components with little fat tissue ( Figures 3B, C ).
Analysis of the resected specimen. The resected specimen showed an ill-defined border (A, x100) and a myxoid and fibrous lesion with spindle cells; some spindle cells had cytological atypia (B, x100 C, x200). Immunohistochemical results for CD34 (D), S100 (E) and RB1 (F) (x200). Fluorescence in situ hybridization indicated no amplification of MDM2 (G) and no rearrangement of FUS (H) or EWSR1 (I).
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Histopathologically, the tumor infiltrated the muscle and had an ill-defined border ( Figure 4A ). In addition, there were areas with fatty lipid and lipoblast components ( Figures 4B, C ). Figure 4D ) and S100 ( Figure 4E ), negative for retinoblastoma (RB1) ( Figure 4F ), and negative for desmin, estrogen receptor, Muc4, and BCL2 (data not shown). FISH showed no amplification of mouse double minute 2 homolog (MDM2) ( Figure 4G ) and no rearrangement of FUS ( Figure 4H ) or EWSR1 ( Figure 4I ).