Intracranial malignant lymphomas. A morphologic and immunocytologic study of twenty cases.

Fifteen primary intracranial reticulum cell sarcomas and five cases with an additional solitary extracranial tumor mass have been studied. For comparison, seven extracranial malignant non-Hodgkin lymphomas and normal lymphoid tissue were included. The methods used on formalin-fixed paraffin-embedded tissue sections were an immunoperoxidase technique for the demonstration of intracellular immunoglobulins, microglial staining, Gomori's reticulin, methylgreen-pyronin, Giemsa, diastase resistant PAS, Mallory's PTAH and H&E. Electron microscopy was performed in one primary brain tumor. According to histopathologic criteria all tumors could be classified as malignant non-Hodgkin lymphomas, predominantly of the pleomorphic immunocytic or of the immunoblastic type; follicular lymphomas were notably absent. In all cases intracellular immunoglobulins were demonstrable in tumor cells and in a majority of the tumors these were monoclonal. Thus, all malignant lymphomas proved to be of B cell origin with demonstrable cytoplasmic immunoglobulin production. Based on the microglial staining more than half of the malignant lymphomas could also be classified as microgliomas. As a comparable staining was present in non-Hodgkin lymphomas outside the CNS, microglioma characteristics are not associated with intracranial growth.