Primary central nervous system lymphoma: CT and pathologic correlation.

CT findings of 15 patients with histologically proven primary central nervous system (CNS) lymphoma were reviewed with pathologic correlation in order to evaluate variable CT patterns. There were a total of 32 lesions. Of the 15 patients studied, seven had acquired immunodeficiency syndrome (AIDS), all diagnosed within the past 3 years. The CT observations of eight non-AIDS patients were consistent with findings reported previously. Most of the lymphomatous lesions were either hyper- or isodense, round or oval masses with homogeneous contrast enhancement and variable surrounding edema. Pathologic examination showed tightly packed preserved lymphoma cells without necrosis. In AIDS patients, rim or ring enhancement of lymphoma, indistinguishable from brain abscess, was frequently seen. Histologic examination consistently showed extensive tumor necrosis with preservation of viable tumor cells at the periphery. A third and infrequent CT pattern was multiple infiltrative nonnodular solid enhancement with extensive edema. Pathologic correlation showed infiltrating viable tumor cells without necrosis. The rim- or ring-enhancing brain lesion seen in AIDS patients can either be an abscess or a primary lymphoma; proper tissue collection is essential for correct diagnosis and appropriate treatment.