Role of imaging in the diagnosis of acute bacterial meningitis and its complications.

Acute bacterial meningitis is a common neurological emergency and a leading cause of death and neurological disability worldwide. Diagnosis is based on clinical and microbiological findings with neuroimaging in the form of CT reserved for those with specific adverse clinical features or when an underlying cause such as mastoiditis is suspected. MRI is extremely useful for detecting and monitoring the complications of meningitis. These can be remembered by the mnemonic HACTIVE (hydrocephalus, abscess, cerebritis/cranial nerve lesion, thrombosis, infarct, ventriculitis/vasculopathy and extra-axial collection). Diffusion weighted imaging (DWI) and magnetic resonance spectroscopy (MRS) are useful to distinguish abscess from other ring enhancing lesions.