PMC5971379_01
Photograph showing the tumor on the left leg (a). X-ray image (sagittal view) of the left knee, (b) T1-weighted magnetic resonance image of the left knee (sagittal view), (c) T2-weighted magnetic resonance image of the left knee (coronal view), (d) contrast-enhanced computed tomography scan of the left knee, (e) 18F-fluorodeoxyglucose positron emission tomography scan of the left knee (coronal view), and (f).the red arrows indicate the location of the tumor.
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On physical examination, an approximate 5 x 5 cm moderately tender mass was noted on the back of the left knee (Figure 1(a)). Radiography of the left knee showed no calcification in the popliteal region (Figure 1(b)). Magnetic resonance imaging showed a 4.7 x 2.95 x 3.35 cm fusiform homogeneous mass arising within the tibial nerve (Figure 1(c)). The mass was lower in intensity than the skeletal muscle on T1-weighting (Figure 1(c)) but higher on T2-weighting (Figure 1(d)). Contrast-enhanced computed tomography revealed that the tumor was in contact with the popliteal artery and vein (Figure 1(e)). 18F-fluorodeoxyglucose positron emission tomography showed slight accumulation of the isotope in the tumor (maximum standardized uptake value, (SUVmax) = 1.48) (Figure 1(f)).
(a) Hematoxylin and eosin staining of a tumor sample, (b) Immunohistochemical staining of vimentin, (c) CD99, (d) epithelial membrane antigen (EMA), (e) S-100, (f) popliteal region after revascularization, (g) appearance of the excised specimen, and (h) appearance of the cut surface of the excised specimen.
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Histopathology of a needle biopsy sample showed dense spindle-shaped cells with oval nuclei with fine chromatin on hematoxylin-eosin staining (Figure 2(a)). The spindle-shaped cells were positive for vimentin (Figure 2(b)) and CD99 (Figure 2(c)), but negative for epithelial membrane antigen (EMA) (Figure 2(d)), S-100 (Figure 2(e)), and keratin. Finally, we rebuilt the popliteal vein in the left leg using the saphenous vein from the right leg (Figure 2(f)). The macroscopic margin was tumor-free (Figure 2(g)). The resected specimen showed an elastic, hard yellowish-white cut tumor surface (Figure 2(h)).