Sections of the mass revealed a highly cellular tumor with numerous slit-like, branching vascular channels (Figure 3). The tumor was vimentin- and CD34-positive (Figure 4), and a “staghorn” vascular pattern was highlighted with a CD31 immunohistochemical stain (Figure 5). Immunohistochemical stains for S-100 protein, synaptophysin, and epithelial membrane antigen (EMA) were negative.
Microscopic Appearance
 Figure 3
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 Figure 4
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 Figure 5
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