[Indication of neuro-imaging for the initial management and the follow-up of acute community-acquired bacterial meningitis].

Lumbar puncture is the best way to prove bacterial meningitis. It should be performed without any delay if the diagnosis is suspected. Herniation is a rare complication of LP. CT is normal in most cases of purulent meningitis, including those complicated by a subsequent herniation; normal CT results does not mean that performing a LP is safe. Three main clinical features can help determine which patient is at risk of herniation and should have a CT before LP. This risk has to be determined rapidly in the emergency ward while assessing anamnestic data, localization signs or symptoms, and level of consciousness. Cranial imaging (mainly MRI) is useful in the course of bacterial meningitis. Patients who do not respond well to treatment or with atypical presentation, persistence of fever, or new neurological signs should undergo brain imaging; MRI and CT may identify subdural effusions, brain abscesses, empyemas, hydrocephaly, or brain parenchymal changes (cerebritis, infarction, hemorrhage). CT and MRI are useful to screen for an ENT cause of bacterial meningitis, and mandatory in case of pneumococcal meningitis. Numerous MRI sequences are useful to identify bacterial meningitis complications: SE T1 without and with gadolinium injection, SE T2, FLAIR, gradient-echo T2, diffusion weighted imaging, MR angiography.