Case: AP130
Contributor's Comment: Most participants render the correct diagnosis of large cell lymphoma. In this case, the neoplastic cells are immunoreactive for CD20, and thus this is a primary large B-cell lymphoma of the central nervous system. Some participants have made the diagnosis of glioblastoma multiforme (or variant) only, and have not considered lymphoma as a possibility. It is important to make a distinction between the two tumours, because treatment is different.
Although there are focal areas in the slide that might look like glioblastoma multiforme, the overall features are more in keeping with a diagnosis of large cell lymphoma. The striking angiocentric growth (with insinuation into the blood vessel walls) is a highly characteristic feature of CNS lymphoma, but is usually not seen in glioblastoma multiforme -- which more often is accompanied by endothelial hyperplasia instead. The basophilic or amphophilic quality of the cytoplasm also differs from the eosinophilic, often hyaline, cytoplasm of the tumor cells characteristic of glioblastoma multiforme. The palisading necrosis typical for glioblastoma multiforme is also not seen in this case.