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.