PMC4001430_01
(a, b) Axial and coronal T1W images showing a hypointense mass in the distal phalanx of the right fifth toe with widespread bone destruction. (c, d) T2W images showing a homogeneous hyperintense mass with cortical bone destruction and extension into subcutaneous soft tissues. (e, f) T1W images with gadolinium enhancement showing heterogeneous enhancement of the lesion.
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Heterogeneous enhancement was observed after gadolinium administration, mainly in the marginal regions (Fig. 1). 
(a) Cell proliferation in a storiform pattern, comprising mostly spindle-shaped cells with clear abundant cytoplasm and atypical hyperchromatic nuclei (hematoxylin and eosin stain, original magnification x40). (b) Immunohistochemical staining for S-100 shows moderately positive results in tumor cells (original magnification x40). (c) No expression of melanA is seen in tumor cells (original magnification x40). (d) Typical spindle cell proliferation infiltrating skeletal tissues (black arrowheads) (hematoxylin and eosin stain, original magnification x4).
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Histological examination of a skin biopsy specimen showed massive cell proliferation in a storiform pattern extending from the superficial dermis to the subcutis, predominantly comprising spindle-shaped clear cells with abundant cytoplasm and atypical hyperchromatic nuclei (Fig. 2a). Immunohistochemical staining for S-100 showed moderately positive results in the atypical spindle cells (Fig. 2b), whereas staining for desmin, alpha-smooth muscle actin, factor XIIIa, CD34, cytokeratin (AE1/AE3), HMB-45, and melanA yielded negative results (Fig. 2c).