Primary non-Hodgkin lymphomas of the CNS. Classification, tissue reaction and proliferative activity.

Primary cerebral lymphomas (PCL) are rare tumors, which, however, occur at increasing frequency. From 1980 to 1991, 44 PCL were histologically diagnosed from immunocompetent patients in our department. According to the updated Kiel Classification, 13.5% of the tumors were of low malignancy (4 immunocytomas, 2 centroblastic-centrocytic), and 79.5% were highly malignant B-cell lymphomas (26 centroblastic, 2 Burkitt-type, 3 immunoblastic, 4 unclassified). Two T-cell lymphomas and one large-cell anaplastic lymphoma were found as well. A reactive tissue infiltrate consisting of varying amounts of small T-cells and tissue macrophages was present in all B-cell lymphomas. PCNA-indices reflected the histological grade, with mean counts of 19.5% in low grade neoplasms and 59.3% in high grade ones. No correlation was found to exist between PCNA-index and patient survival.