Flow Cytometric Immunophenotyping of Cerebrospinal Fluid for the Detection of Central Nervous System Involvement in...

Central nervous system (CNS) involvement in patients with hematological malignancies is traditionally assessed by microscopic examination of cerebrospinal fluid (CSF). However, this method has limited sensitivity and specificity. In contrast, flow cytometric immunophenotyping (FCI) is a highly sensitive technique capable of objectively detecting even small populations of tumor cells.This retrospective study analyzed CSF flow cytometry findings in patients with various hematological malignancies. A custom-designed, single-tube, 6 to 10 color panel was used, tailored according to the primary diagnosis. Paired samples were evaluated to compare the diagnostic performance of cytospin smear morphology and FCI.A total of 404 paired CSF samples were analysed, which included 283 diagnostic and 121 follow-up samples. FCI identified malignant cells and was labelled positive in 67 samples (16.6%). The median number of viable, live-gated cells analyzed per sample was 1,537 (range: 68-182,000), with a median atypical cell proportion of 43% (range: 0.4%-98%). Among the FCI-positive samples, only 29 (43.2%) were also positive on cytomorphological assessment. Conversely, eight samples were positive on morphology but negative on FCI-four of which were B-cell non-Hodgkin lymphomas (including Burkitt lymphoma and DLBCL). The overall discordance rate between FCI and cytomorphology was 11.5%. FCI is a highly sensitive and specific method for detecting malignant cells in CSF, even in paucicellular samples. Morphology can be deceptive and thus it may be prudent to subject the paucicellular CSF sample for a direct FCI evaluation in cases of Acute leukemia. For large cell lymphomas, a meticulous cytomorphological evaluation can provide complementary diagnostic value.

The online version contains supplementary material available at https://doi.org/10.1007/s12288-025-02201-w.