Malignant lymphomas involving the central nervous system--a morphological and immunohistochemical study of 32 cases.

The morphological features of 32 cases of malignant lymphomas involving the central nervous system presenting over a 32 year period were reviewed and the lymphomas redefined using current classifications. Twenty-four cases (75%) of non-Hodgkin's lymphomas were reclassified using the Kiel classification. There were 18 low grade non-Hodgkin's lymphomas (comprising 11 lymphoplasmacytoid, five lymphocytic and two centroblastic-centrocytic) and six high grade tumours (comprising two centroblastic, two immunoblastic, one unclassifiable and one lymphoblastic lymphoma). Cytologically the great majority of non-Hodgkin's lymphomas were B-cell lymphomas. The eight cases (25%) of Hodgkin's disease were classified by the Rye subtype and consisted of three mixed cellularity, two lymphocyte depletion, two lymphocyte predominant and one nodular sclerosis. The presence of intracytoplasmic immunoglobulins as well as markers for histiocytic cells were studied by the immunoperoxidase technique using polyclonal antisera. A monoclonal staining pattern, as revealed by light chain restriction, was found in nine cases (38%) of the non-Hodgkin's lymphomas confirming their B-cell origin. With the Marshall's metalophil method and the other histiocytic markers, scattered reactive microglial cells and histiocytic reticulum cells were found throughout the tumours in most cases. No histiocytic lymphomas were present in the series.