Cerebrospinal fluid pleocytosis in aseptic meningitis: cytomorphic and immunocytochemical features.

We report five cases of aseptic meningitis presenting with high cerebrospinal fluid (CSF) cell counts (260-600 cells/cmm) and mononuclear pleocytosis, suggesting the diagnosis of CNS malignant lymphoma. In four of five cases a reactive background of small lymphocytes, monocytes, and eosinophils was seen. Immunocytochemical studies in all five cases revealed that 100% of the lymphoid cells were T-cells. Three of four cases evaluated for lymphocyte subsets displayed a CD4 to CD8 ratio of 3:1. In the fourth case the CD4:CD8 was 1 to greater than 10; this patient was subsequently proven to have AIDS with HIV meningitis. In this study the cytologic features of the benign atypical lymphoid pleocytosis of aseptic meningitis in contrast to malignant lymphomas in CSF specimens included small or indistinct nucleolus, regular perinucleolar area, smaller widely separated chromatin aggregates, generally ample cytoplasm with perinuclear clearing and polyclonal T-cell immunophenotype.