CSF Involvement by Nonhematolymphoid Malignancies: A Descriptive Study with Emphasis on Cytomorphological Clues.

Introduction: Detection of malignant cells in cerebrospinal fluid (CSF) samples in suspected cases of malignancy is critical for the management of patients. CSF involvement by nonhaematolymphoid malignancies is less common. We aimed to study the cytomorphologic characteristics of various nonhaematolymphoid malignancies in CSF. Methods: A retrospective cytomorphological analysis of 27 CSF cytology smears reported as positive or suspicious for nonhematolymphoid malignancies from January 2010 to April 2020 over 10 years was carried out. Smears in all cases were prepared by cytospin technique and stained with May-Grunwald-Giemsa (MGG) and papanicolaou (Pap) staining procedures. Cell immunohistochemistry/immunocytochemistry was done wherever cell block/extra slides were available. Results: Twenty-four of 27 cases were interpreted as "positive," while three were reported as "suspicious" of malignancy. Nineteen of 27 cases were metastatic adenocarcinomas including three suspicious malignancy cases with the primary sites of origin being the breast (10), stomach (2), rectum (1), gall bladder (1), lung (1), and four cases of unknown primary. Of the remaining positive cases, there were five cases of metastatic medulloblastoma, two cases of metastatic pineoblastomas, and one case of metastatic extraskeletal Ewings sarcoma. Each of these metastatic malignancies had at least a single diagnostic cytomorphological clue, similar to those observed in other body cavities and primary malignancy sites. Conclusion: Nonhematolymphoid malignancies are readily diagnosable on CSF cytology, most of them are metastatic. Identification of malignant cells in CSF is critical, as it has therapeutic and prognostic implications.