Cerebrospinal fluid cytomorphology identification of benign cells originating in the central nervous system

The chief cellular consituents of CSF are the "free cells" of the pia-arachnoid, ependyma, and choroid. These cells are of diverse types, but have their mesenchymal origin in common. Usually they offer no difficulty in identification since they are predominantly histiocytic. However, these "free cells" may be morphologically changed in reaction to an appropriate stimulus, and may therefore be a source of error in diagnostic material. Cells having mesothelial characteristics are not found in the CSF compartment and therefore the term pia-arachnoid mesothelial cells appears inappropriate. The only neuroectodermal derivative that was easily identifiable was the choroidal cell. It is distinctive and unequivocal. We were unable to recognize ependymal cells in our present study. Glial cells (protoplasmic and fibrous astrocytes) and neurons can be recognized when neural tissue is penetrated in the process of collecting CSF.