The comprehension of bacterial and fungal infections of nervous system first requires knowledge of anatomy because the consequences of infection vary both with the anatomical spaces involved and the functions of the tissues located within them. Although a few organisms are notable for their ability to cross tissue planes, most infections, initially manifest in one or two spaces. Epidural infections are typically excluded from either direct extension into or immunological effects compromising the central nervous system (CNS) structures. The manifestations of these infections are primarily due to compression of adjacent tissues. The brain or spinal cord themselves may become infected, initially in the form of cerebritis or myelitis, which then evolve into a parenchymal abscess. The blood vessels may also become infected; producing either an arteritis (also termed vasculitis). When veins or venous sinuses are involved, the pathophysiological consequences are typically due to thrombosis, so the terms septic venous thrombosis or sinus thrombosis are often employed. Bacteria and fungi, by virtue of their intrinsic properties and the host responses they incite, tend to produce specific clinical syndromes when they infect the nervous system. Because the host's defenses play such a critical part in shaping the signs and symptoms, abnormalities of host response may cause different syndromes in different patients infected with the same organism.
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