Malignant small round cell tumor - ulna
Forearm pain and swelling.
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The intramedullary tumor involved nearly the full length of the ulna, with the exception of the proximal olecranon. The surrounding cortex also is involved, and the soft-tissue components at the dorsal and ulnar sides appeared hyperintense due to edema.
Microscopic appearance is related to malignant round cell tumor.
Tumor necrosis and sheet-like distribution of the neoplastic cells is seen.
The cells have scant cytoplasm, coarse nuclear chromatin and high nuclear to cytoplasmic ratio.
The neoplastic cells also show a strong and diffusive membranous CD99 reactivity.