Cytology of primary central nervous system neoplasms in cerebrospinal fluid specimens.

Although two-thirds of tumors occurring in the central nervous system (CNS) are primary neoplasms, only 10% of positive cerebrospinal fluid (CSF) specimens are from primary CNS tumors. In this study, we reviewed the cytologic findings of 21 positive CSF specimens from primary CNS tumors. A computer search identified 21 cases of positive CSF specimens from patients with primary CNS tumors from the archives. Follow-up included review of medical charts and histologic correlation. The specimens were from 20 patients (9 females and 11 males). Their ages ranged from 6-83 yr, old with a mean of 30 yr. The cases included 9 medulloblastomas, 7 gliomas (3 glioblastoma multiformes, 2 anaplastic astrocytomas, and 2 ependymomas), 2 germinomas, 2 non-Hodgkin's large B-cell lymphomas, and 1 ganglioneurocytoma. Two cases were classified as suspicious and the remaining as positive for malignancy. Immunocytochemistry was employed in 3 cases to support the cytologic diagnosis. These cases included one large-cell lymphoma (leukocyte-common antigen-positive), one germinoma (placental alkaline phosphatase-positive), and the ganglioneurocytoma (neuron-specific enolase- and synaptophysin-positive). There were no false-positive cases. Our results suggest that positive CSF cytology in patients with a primary CNS tumor is a reliable indicator of malignancy and reflects leptomeningeal involvement. The use of immunocytochemistry is helpful in confirming the cytologic impression in some cases.