Flow cytometry of cerebrospinal fluid demonstrates lymphoma

This flow cytometry study of a sample of lymphocytes obtained from the cerebrospinal fluid of a patient with suspected lymphoma shows a population of B-lymphocytes (green color, asterisk) which stains positive for kappa light chains (Y axis) and positive for CD19 expression (x axis). This same CD19 positive cell population stained negative for lambda light chain expression (not shown here), identifying this as a monoclonal population of lymphocytes, and suggesting that these cells represent involvement of the neuraxis with lymphoma.