When Ventricular Cerebrospinal Fluid Assessment Misleads: Basal Meningitis and the Importance of Lumbar Puncture Sampling.

The diagnosis of central nervous system (CNS) infection relies upon analysis of cerebrospinal fluid (CSF). We present 4 cases of CNS infections associated with basal meningitis and hydrocephalus with normal ventricular CSF but grossly abnormal lumbar CSF. We discuss CSF ventricular-lumbar composition gradients and putative pathophysiological mechanisms and highlight clinical clues for clinicians.