Background: Involvement of the cerebrospinal fluid (CSF) by hematopoietic malignancies may be difficult to document by morphology alone. In cases with low numbers of cells or ambiguous morphology, the diagnoses of "atypical" or "suspicious" may be used. The significance of these diagnostic terms in this scenario has not been well established.
Methods: Between January 2000 and July 2004, 32 patients with known lymphoma or leukemia and an initial diagnosis of "atypical" or "suspicious" using morphologic criteria were identified. Subsequent flow cytometry (FC) and cytologic data from these patients were evaluated.
Results: Of the 32 patients with an initial diagnosis of "atypical" or "suspicious," 40.6% (n = 13) had negative first and subsequent FC and morphologic evaluation of their CSF samples with follow-up up to 1 year. Nineteen patients (59.4%) had malignant hematopoietic cells identified in subsequent CSF samples by cytology and/or FC.
Conclusions: In patients with a previous history of lymphoma or a hematopoietic malignancy, a majority of the patients (59.4%) with an "atypical" or "suspicious" diagnosis on CSF will ultimately have malignant cells identified in the CSF by cytology and/or FC. Many of these patients can be identified more expediently with the concurrent utilization of flow cytometry.