Utility of Flow Cytometry in the Evaluation of Cerebrospinal Fluid in Hematolymphoid Malignancies: A Prospective Study

Background: Central nervous system (CNS) involvement in hematolymphoid malignancies poses a diagnostic challenge and is associated with poor prognosis. Flow cytometry (FCM) has emerged as a sensitive diagnostic tool for detecting malignant cells in cerebrospinal fluid (CSF). Objectives: The objective of this study was to evaluate the diagnostic utility of FCM in CSF of patients with suspected hematolymphoid malignancies and to describe their clinicopathological spectrum. Materials and Methods: This prospective study included 42 patients from January 2024 to March 2025. CSF samples were analyzed through cytomorphology and FCM using lineage-specific panels. Statistical analyses included frequency distribution and correlation of FCM results with clinical, radiological, and bone marrow findings. Results: The mean patient age was 22.26 ± 19.03 years. FCM detected CNS involvement in 90.4% of cases. In terms of final hematological diagnosis, B-cell acute lymphoblastic leukemia (B-ALL) was the most frequent, diagnosed in 24 patients (61.9%), followed by acute myeloid leukemia, diffuse large B-cell lymphoma, and T-cell ALL. Chronic myeloid leukemia, multiple myeloma, and Burkitt’s lymphoma were also diagnosed, although in fewer numbers. Morphologically, the presence of B-lymphoblasts was observed in 38.1% of CSF samples, making it the most common cellular abnormality. This was followed by atypical lymphoid cells (21.4%) and blastoid cells (9.5%), whereas a few samples showed plasma cells, large clonal lymphoid cells, or were reported as negative for blasts. Hence, FCM increases the sensitivity and specificity of detection significantly. Conclusion: FCM significantly enhances the detection of malignant cells in CSF, even in paucicellular samples, proving its utility in routine CNS evaluation in hematolymphoid malignancies.