Deceptively normal ventricular fluid in lymphomatous meningitis.

The diagnosis of leptomeningeal cancer ultimately depends on the finding of abnormal cerebrospinal fluid with malignant cytologic study results. We report a case of relapsed leptomeningeal lymphomatosis in which ventricular cerebrospinal fluid was entirely normal while lumbar spinal fluid was diagnostically abnormal. To our knowledge, this is the first such reported case, and it highlights the importance of sampling cerebrospinal fluid close to the site of clinical involvement.