This patient had a prior history of renal cell carcinoma and nephrectomy 2 years previously without evidence of metastatic disease. He went on to have a craniotomy and resection of the mass, at which time it was still difficult to identify the site of origin as both the choroid plexus and adjacent brain were involved.
MICROSCOPIC DESCRIPTION: Sections show a moderately cellular tumour surrounded by pools of blood and only a small amount of brain parenchyma. The tumour comprises clusters of cells intersected by a rich vascular network. The tumour cells have ovoid mildly pleomorphic nuclei, inconspicuous nucleoli and moderate amount of granular to clear eosinophilic cytoplasm. Some cells show well defined cytoplasmic outlines. Mitotic activity is inconspicuous.
The tumour cells are CD10 and Vimentin positive but Inhibin, S-100, CK7, CK20, TTF-1, CDX-2 negative. The morphological and immunohistochemical features are of a metastatic renal cell carcinoma.
FINAL DIAGNOSIS: Metastatic renal cell carcinoma.