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Infectious Diseases of the Central Nervous SystemGary Baumbach, M.D.Department of Pathology The University of Iowa College of Medicine
Peer Review Status: Internally Peer Reviewed |
Introduction
This tutorial is designed to provide an overview of the various infectious disease processes which involve the central nervous system (CNS). The intent is to give relatively complete information about all of the important infectious diseases of the CNS without overwhelming detail.
For purposes of organization, infections of the CNS can be divided into two broad categories - those which involve primarily the meninges, and those which are confined primarily to the parenchyma.
Under the heading of meningeal infections, we will consider general concepts after which three basic categories will be discussed: pyogenic meningitis, granulomatous meningitis, and lymphocytic meningitis. These categories represent different types of inflammatory responses. Many textbooks divide meningeal infections on the basis of the causative organism. The advantage of categorization by inflammatory type is that it provides a more logical framework for relating the pathological findings to the causative organism. Other considerations in this section include complications and CSF findings in meningitis.
In contrast to the organization of meningeal infections, parenchymal infections have been organized in terms of the various types of organisms which include syphilis, parasites, fungi, viruses, and prions (scrapie, kuru & Creutzfeldt-Jakob disease). The one exception to this approach is the topic of cerebral abscesses. For practical purposes, you could replace the term "abscess" on this slide with the term "bacterial," since most cerebral abscesses are caused by bacterial infections of the parenchyma. However, certain fungi and parasites are also capable of producing an abscess. In addition, cerebral abscesses have several distinctive features both clinically and pathologically, regardless of the causative organism.
Finally, before proceeding with the specific infectious diseases, the definitions of at least two terms should be made clear: cerebritis and encephalitis. Both of these terms imply inflammation of parenchyma in the cerebrum, and on occasion are used interchangeably. However, by convention these terms do have specific and different meanings among practicing neuropathologists. Cerebritis means inflammation of all tissues in the brain substance, and is used to indicate a stage preliminary to abscess formation. Thus, cerebritis is a very destructive process and implies bacterial infection. Encephaltitis, on the other hand, means inflammation of brain tissue secondary to viral infection. Inflammation in encephalitis is not usually as intense as in cerebritis, and the destruction, while still profound, is not usually as great. Myelitis is the counterpart of encephalitis in the spinal cord.