Bone marrow contamination of canine cerebrospinal fluid

Bone marrow cells were identified in cytocentrifuge preparations of cerebrospinal fluid (CSF) obtained by lumbar punctures from two dogs. CSF analyses were characterized by normal or increased total cell counts, normal or increased total protein concentration and the presence of erythrocytes. Hematopoietic cells present included both erythroid and myeloid precursors and, in one case, an erythroblastic island was seen. Peripheral blood smear examination confirmed that the hematopoietic cells observed were not the result of blood contamination. Neither case was associated with a difficult tap procedure, nor with a specific disease process. Contamination may have resulted from actual marrow penetration or from extramedullary hematopoiesis in the dura mater. Accurate interpretation of CSF cytology requires the consideration of possible bone marrow contamination when hematopoietic cells are observed.