PMC3926977_01
CT images of the left thigh. (a) Transverse image. (b) Coronal image. A high-resolution volumetric CT scanning revealed a 9.7 x 11 x 19 cm irregularly shaped soft tissue mass in the anteromedial left thigh (yellow arrow) and a partial bone defect approximately 9.7 cm in length on the medial border of the left femur shaft (light blue arrow).
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F1
A 9.7 x 11 x 19 cm irregularly shaped soft tissue mass was observed around the left femur, with the surrounding tissues compressed and shifted significantly (Figure  1).
Histopathological examination of the tumor. (a) Magnification, x40. (b) Magnification, x100. H&E staining showed that the tumor was predominantly composed of a large number of diffuse fusiform cells and myxoid matrix. The fusiform tumor cells were arranged in a multi-nodular pattern, with indistinct cell margins, slightly eosinophilic cytoplasm, and hyperchromatic atypical nuclei. Mitoses were infrequent. Many elongated curvilinear capillaries were observed.
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F2
In addition, many elongated curvilinear capillaries were observed (Figure  2).
Immunohistochemical studies of the tumor. (a-i) Magnification, x200. The tumor cells expressed strong immunoreactivity for VIM (a) and negative for CK (b). Labeling index of Ki-67 (c) was 25%. MSA (d), SMA (e), DES (f) and S-100 protein (g) were negative in the tumor cells. (h) CD34 staining was detected in vascular endothelial cells rather than in tumor cells, highlighting the curvilinear capillaries. (i) MDM2 was positive in the tumor cells.
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F3
Immunohistochemical studies showed that the tumor cells expressed strong immunoreactivity for vimentin (VIM) and negative for cytokeratin (CK), suggesting a mesenchymal histogenesis (Figure  3a and b). Labeling index of Ki-67 (the number of Ki-67 positive tumor cells divided by the sum of Ki-67 positive and negative tumor cells) was 25% (Figure  3c). Muscle-specific actin (MSA), smooth muscle actin (SMA) and desmin (DES) were negative in the tumor cells, eliminating the possibility of a muscle-derived tumor (Figure  3d-f) . The negative expression of S-100 protein eliminated a tumor of neural or adipose tissue origin (Figure  3g). The tumor cells were negative for cluster of differentiation 34 (CD34) (Figure  3h), B cell lymphoma/lewkmia-2 and anaplastic lymphoma kinase, which eliminated the possibility of a solitary fibrous tumor or inflammatory myofibroblastic tumor .
MRI images of the thigh. (a) Transverse T2-weighted image. (b) Coronal T1-weighted image. MRI images showed an irregular soft tissue mass with ill-defined margin in the anteromedial left thigh (yellow arrow), accompanied by surrounding soft tissue swelling and normal muscle structure disappearance. Bone destruction in the left femur shaft was observed (light blue arrow).
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F4
Additionally, bone destruction in the left femur shaft was also observed (Figure  4).
Histopathological examination of the recurrent tumor. (a) Magnification, x200. (b) Magnification, x400. H&E staining showed that the tumor cells exhibited increased atypia and pleomorphism compared with those in the primary tumor, varying from small and bland to enlarged, bizarre, pleomorphic and multinucleated. Abundant myxoid matrix and elongated curvilinear capillaries were also observed.
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F5
The morphology of the tumor cells varied from small and bland to enlarged, bizarre, pleomorphic and multinucleated, suggesting increased atypia and pleomorphism compared with those in the primary tumor (Figure  5).