The patient went on to have a resection.
Paraffin sections show a densely hypercellular tumour within cerebral white matter. Tumour is sharply demarcated from adjacent brain parenchyma and is composed of cells with pleomorphic round, oval and angulated hyperchromatic nuclei and a variable amount of pale to clear cytoplasm. These are dispersed in an intensely vascular stroma with lobules of tumour delimited by thin walled capillaries. An occasional mitotic figure is identified and there is focal tumour necrosis. The features are most consistent with metastatic renal cell carcinoma.
IMMUNOHISTOCHEMISTRY: Tumour cells sho strong staining for pancytokeratin AE1/AE3 and moderate staining for CAM5.2. No staining for CD10 or Inhibin is seen in tumour cells. This profile is consistent with a renal cell origin of tumour.
FINAL DIAGNOSIS: metastatic renal cell carcinoma.