Cerebrospinal fluid cytology in patients with cancer

Detection of malignant cells on cytologic examination of the cerebrospinal fluid (CSF) is the diagnostic gold standard for leptomeningeal carcinomatosis. The absence of cells is a primary endpoint for most therapeutic trials. Unfortunately, false-negative results are common. Practical strategies are necessary to remedy this problem.Four physician-dependent variables (CSF sample volume, site of CSF sampling, processing time, and frequency of CSF sampling) were identified, and their contributions to the false-negative rate of CSF cytology were evaluated prospectively in 39 patients with leptomeningeal carcinomatosis. Retrospective data were analyzed to estimate the importance of these variables in daily practice.False-negative CSF cytology results correlated with small CSF volume (P < 0.001), delayed processing (P < 0.001), not obtaining CSF from a site of symptomatic or radiographically demonstrated disease (P = 0.02), and sampling fewer than two times (P < 0.001). In 1 year, 97% of CSF specimens at the study institution were of inadequate volume; >25% were processed too slowly.False-negative CSF cytology results are common, but can be minimized by: 1) withdrawing at least 10.5 mL of CSF for cytologic analysis; 2) processing the CSF specimen immediately; 3) obtaining CSF from a site of known leptomeningeal disease; and 4) repeating this procedure once if the initial cytology is negative.