Throughout the book, reference is made to the ways in which changes in the cerebrospinal fluid (CSF) reflect the basic pathologic processes in a variety of inflammatory and infectious, neoplastic, demyelinative, and degenerative diseases. The CSF findings in these circumstances raise so many important problems that we consider it worthwhile to discuss in one chapter the mechanisms of the formation, circulation, and absorption of the CSF, particularly as they pertain to alterations of intracranial pressure (ICP). The diseases that result from perturbations in these mechanisms, mainly hydrocephalus, pseudotumor cerebri, and syndromes of reduced pressure in the CSF compartment, are also presented. Further information on the management of raised ICP, particularly as it pertains to traumatic brain injury, can be found in Chap. 34. Examination of the CSF as a diagnostic aid in neurology was discussed in Chap. 2, and the primary infectious and noninfectious inflammatory reactions of the pia-arachnoid (leptomeninges) and ependyma of the ventricles are considered in Chap. 31.
A few historical points call to mind that our understanding of the physiology, chemistry, and cytology of the CSF is the result of a technical innovation that was introduced over a century ago. Although the lumbar puncture was introduced by Quincke in 1891, it was not until 1912 that Mestrezat made correlations between disease processes and the cellular and chemical changes in the CSF. In 1937, Merritt and Fremont-Smith published a monograph on CSF changes in a broad range of diseases. Our knowledge of CSF cytology starting in the late 1950s, when membrane filtration techniques (particularly the cellulose ester or Millipore filter) were introduced. The studies of Dandy (1919) and of Weed (1935) provided the basis of our knowledge of CSF formation, circulation, and absorption. The important studies of Pappenheimer and colleagues and of Ames and colleagues followed, and then the monographs of Fishman and of Davson and coworkers, which are important and relatively contemporary contributions. (See Chap. 2 for references.) More recent inceptions in analyzing the lymphocytic cells and protein fractions in the CSF for diagnostic and investigational purposes in cancer, multiple sclerosis, markers for degenerative conditions, particularly Alzheimer’s disease, and genetic analysis of organisms in CSF infections, have expanded on new genetic analysis technology.
PHYSIOLOGY OF THE CEREBROSPINAL FLUID
A major function of the CSF appears to be a mechanical one; it serves as a kind of water jacket for the spinal cord and brain, protecting them from potentially injurious blows to the spinal column and skull and from acute changes in venous pressure. In doing so, it provides the brain with buoyancy. The 1,500-g brain, which has a water content of approximately 80 percent, weighs only 50 g when suspended in CSF, so the brain virtually floats in its CSF (Fishman). Many of the physiologic mechanisms described below are committed to maintaining the relatively constant volume–pressure relationships of the CSF. In addition, the CSF, ...