Lesions
Pathologic changes characteristic of meningitis include diffuse infiltration of leukocytes into the leptomeninges. Frequently, the entire subarachnoid space of the brain and spinal cord is inflamed. Vasculitis of meningeal vessels and CNS arterioles may also be apparent. In meningoencephalitis, the inflammation extends into the CNS parenchyma, resulting in leukocyte infiltration with large areas of perivascular cuffing. Necrosis and malacia of the CNS may be seen, with infiltrations of macrophages, neutrophils, and plasma cells. Listeriosis uniquely causes microabscesses deep within the CNS parenchyma, which consist of accumulations of neutrophils and microglial cell reaction with central liquefactive necrosis.