Micrographs A-C: Left temporal lobe tumour. Primitive-appearing blue cell neoplasm, large areas of necrosis, and fragments of brain parenchyma. Neoplastic cells have round to angulated, pleomorphic, hyperchromatic nuclei associated with scant amounts of cytoplasm and are arranged in sheets. There are numerous mitoses.
C: Left temporal lobe tumour staining positively for MPO.
D: Left temporal lobe tumour staining positively for CD 117.
E. Sections of cancellous left temporal bone bone show deposits of primitive appearing small blue cell neoplasm in the marrow space, morphologically similar, with features of remodelling.
F. Sections of skeletal (left temporalis) muscle and connective tissue show similar morphology to the myeloid sarcoma in the left temporal lobe. MPO immunohistochemistry is diffusely positive in infiltrating cells.
Immunohistochemical stains:
MPO: Diffusely positive.
CD117: Diffuse positivity, mildly patchy.
Synaptophysin: Highlights neuropil in areas of invasion.
CD68: Largely negative.
S100: Negative.
Cytokeratin: Negative.
CD20: Negative.
CD3: Highlights reactive background T cells.