Purulent meningitis is due most often to hematogenous spread of bacteria to the leptomeninges.
It can also be seen after head trauma as skull fracture through the sinuses. Local infections such as mastoiditis may also lead to meningitis. The most comman bacteria causing meningitis in neonates are streptococcus and E. Coli. In young children and adults Hemophilus influenzae, is common and in adults meningiococcus and pneumococcus are common. Bacteria extend through the wall of blood vessels into the subarachnoid space followed more slowly by neutrophils as the blood brain barrier breaks down.