[Primary Meningeal Lymphoma Diagnosed Using Cytology and Flow Cytometry-A Case Report].

A 72-year-old male was referred with a 2-week history of diplopia. Following magnetic resonance imaging, an area of abnormal signal intensity was observed along the lateral ventricle, without any unusual findings at other sites. Cerebrospinal fluid cytology revealed abnormal lymphocytes with atypia, which were positive for CD20 and light-chain restriction, as detected by surface marker analysis, leading to a diagnosis of primary meningeal B-cell lymphoma.