The patient went on to have surgery.
MICROSCOPIC DESCRIPTION: Paraffin sections show fragments of white matter in which there is edema and reactive astrocytic gliosis. No evidence of tumor is seen. Paraffin sections show fragments of densely hypercellular tissue. These are composed of diffuse sheets of cells with large vesicular nuclei, many with conspicuous sometimes multiple nucleoli and a narrow rim of pale cytoplasm. Frequent mitotic and apoptotic figures are noted and there are scattered small foci of necrosis.
Immunohistochemistry results show tumor cells stain: CD10+, CD20+, BCL2+, BCL6+, MUM1+, CD30- and EBER-CISH-. The CD3 and CD5 stains highlight background T-cells. The features are of those of diffuse large B cell lymphoma, consistent with a germinal center immunophenotype.
FINAL DIAGNOSIS: Brain tissue insula: White matter with reactive changes only; no evidence tumor seen. Brain tissue insula: Diffuse large B cell lymphoma, germinal center type.
This example illustrates not only fairly typical appearances of CNS lymphoma, but also the response to steroid.