Utility and performance of cell blocks in cerebrospinal fluid cytology: Experience at two teaching hospitals.

Background: Cytology cell blocks (CBs) are not routinely made for cerebrospinal fluid (CSF) specimens. The goal of this study was to identify when CSF CB preparation improves diagnostic performance. Materials and Methods: Under institutional review board approval, a retrospective review of CSF cytology cases was conducted at a tertiary university‐based hospital and an affiliated county hospital. Patient history, CSF volume, final diagnosis, use of stains, and whether the CB was contributory was determined from the cytopathology report. CSF nucleated cell count data was obtained from the medical record. Results: A total of 69 CSF specimens with CBs from January 2006 to March 2023 were identified from 61 patients. The median CSF volume was 8 mL (interquartile range, 4–13 mL; range, 1–800 mL), with immunohistochemical stains performed on 29 (42%) cases. Per cytology report, CB was contributory in 23 cases (33%), not contributory in 34 cases (49%), and not discussed in 12 cases (17%). The median volume was 8 mL for cases in which CB was contributory, not contributory, or not discussed. There was no difference in average nucleated cell counts between cases in which CB was contributory versus not contributory (73.9 vs. 40.0, p =.175). Conclusions: CBs for CSF samples were contributory in a subset (33%) of cases. The authors were unable to identify any specific pre‐analytic factors, including specimen volume and average nucleated cell counts, for cases in which CB was contributory. Further evaluation is needed to identify if there are scenarios in which CSF CBs should be routinely prepared. Cytology cell blocks (CBs) are not routinely made for cerebrospinal fluid (CSF) specimens. In a retrospective review of CSF cytology cases at a tertiary university‐based hospital and an affiliated county hospital, CBs for CSF samples were contributory in a subset (33%) of cases. [ABSTRACT FROM AUTHOR]