The CSF Gram stain showed Gram-positive diplococci, subsequently growing S. pneumoniae. A peripheral blood culture revealed the same organism.

There is thickening and opacification of the meninges. Pus can be seen filling the sulci.

A neutrophilic exudate can be seen in the meninges. Neutrophils in the subarachnoid space can infiltrate and damage cranial nerves leading to focal deficits. Invasion into leptomeningeal blood vessels may lead to thrombosis and ischemic infarction. Blood vessels are dilated and congested. If the infection resolves, the fibrinopurulent exudate can organize into fibrous tissue that blocks the exits of the fourth ventricle and impairs CSF flow around the cerebral convexities, which may lead to hydrocephalus. Bacteria and neutrophils don’t usually gain access to the brain parenchyma due to the glia limitans, a thick mesh of astrocytic processes joined by dense junctions; therefore, brain abscesses are only a rare complication.