Viral meningitis: In contrast to the fibrinopurulent exudate that characterizes an acute suppurative meningitis, viral meningitis evokes from the onset a mononuclear response. The majority of these mononuclear cells are lymphocytes, as seen in this photomicrograph of leptomeninges and underlying cortex. Note that in viral meningitis the pathologic process is limited to the subarachnoid space.