Intraventricular B cell lymphoma
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MRI demonstrates multiple masses that appear intraventricular, found in the fourth ventricle, the pineal recess, the floor of the the third ventricle above the mammillary bodies, and the infundibular recess. There is quite pronounced high T2 signal in the adjacent parenchyma. The masses are near isointense on T1 and T2, demonstrate restricted diffusion and marked homogeneous contrast enhancement.
This case demonstrates the predilection primary CNS lymphoma has for the periventricular region, as well as the characteristic signal intensity and homogeneous contrast enhancement.
Sections show a tumor comprised of round cells with hyperchromatic nuclei. There is individual cell karyorrhexis. Mitotic figures are seen. Immunohistochemistry shows that the tumor is negative for the neuronal markers synaptophysin and phosphorylated neurofilament. The Bielschowsky stain is also unremarkable. The tumor cells are negative for glial fibrillary acidic protein (GFAP). The tumor is intensely positive for leukocyte common antigen (CD45). It is also positive for CD20. There is slight expression of CD10. Bcl-2 protein is negative. Many cells are positive for MIB1.
Final diagnosis comment: [The] tumor is a lymphoma. It is best characterized as a diffuse large B-cell lymphoma. The immunophenotype suggested possibility of Burkitt's lymphoma and suggested consideration of testing for HIV, but given the histological findings and the anatomic site it is felt that diffuse large B-cell lymphoma is more likely.