Diffusely effacing the cortex and medulla is an infiltrative, densely cellular neoplasm composed of sheets of monomorphic round cells. Cells have generally distinct borders and scant eosinophilic granular cytoplasm. Nuclei are large and irregularly round with coarsely stippled chromatin, and 1-2 prominent nucleoli. Mitoses average 5 per high power field. Multifocally, neoplastic cells are within vessels, lymphatics, sinuses, and expand perinodal adipose tissue. There is scattered single cell necrosis of neoplastic cells. Subcapsular and medullary sinuses contain moderate hemorrhage, small amounts of fibrin, increased numbers of histiocytes (histiocytosis) that demonstrate erythrophagocytosis and hemosiderosis. The capsule and perinodal adipose tissues are mildly expanded by variable amounts of hemorrhage, lymphocytes and macrophages; rare neutrophils; and mild edema.