Brandi,
You are right, there is not enough information to arrive to a most accurate Diagnosis code, in most cases in Pathology, you don't get enough clinical information to properly assign a diagnosis, especially in cases in which the specimen came from an outside laboratory. Even the Pathologist does not have the access to the clinical information in some of the specimen they are examining. That is why, I can not stress more the importance of clinical data in Pathology coding. I chose 792.0 for the reason that the CSF is abnormal, and due to lack of Specificity in ICD-9, for a malignant CSF, then the malignant is abnormal. You are right, Malignant CSF is harmful, that is why, it warrants for an additional study like Flow Cytometry to assess the hematopoietic tissue for Lymphoma or Leukemia, Molecular Diagnostic to identify infection, like Meningitis, Bacteria, Fungi and parasites. and Surgical Pathology to identify Tumor and it's origin. Malignant does not necessarily means Neoplasm unless confirm by the Pathologist, but it is harmful to the patient.I suggest that if you have those documentation from additional study, then wait until the result is establish to code the CSF cytopathology, if not assigning 792.0 would be appropriate if nothing else. Just my opinion.
Rod