The sections show a densely cellular glial tumour. It is relatively well-demarcated from the surrounding cerebral cortex, though the occasional single tumour cells are present in the cortex. Some of the tumour cells are markedly pleomorphic. They have enlarged hyperchromatic nuclei with frequent intranuclear pseudoinclusions, multinucleation and inconspicuous nucleoli. The cytoplasm is focally foamy and "xanthomatous". Other tumour cells are more spindled with elongated nuclei and cytoplasm. Small numbers of tumour cells are seen at the grey-white matter junction. Many eosinophilic granular bodies are seen. There is perivascular cuffing of lymphocytes. Very sparse mitoses are identified (0-1 mitosis per 10 high-power fields). There is no evidence of endothelial cell hyperplasia or necrosis.
The tumour cells are GFAP positive, and focally synaptophysin and NeuN positive (not shown).
The Ki-67 index is about 1-2%. The features are those of pleomorphic xanthoastrocytoma.
DIAGNOSIS: pleomorphic xanthoastrocytoma (WHO grade II).