The CSF abnormalities identified are also dependent on the CSF collection site with respect to lesion location ( Thomson, Kornegay, & Stevens (1989), Thomson, Kornegay, & Stevens (1990)). Previous therapy may affect the type, degree, and duration of CSF ( Jamison and Lumsden, 1988) abnormalities as well. Additionally, the type and degree of CSF abnormality seem to be related as much to the location of disease as to the cause or the severity of lesion meningeal and paraventricular diseases generally produce greater abnormalities than deep parenchymal diseases. The possible alterations of CSF are relatively limited compared to the varieties of neurological diseases that exist (particularly if the analysis is restricted to total cell counts and total protein determination). Similar to a complete blood count, CSF analysis has reasonable sensitivity but low specificity. CSF analysis is a general index of neurological health and often provides evidence of the presence of disease. The analysis of cerebrospinal fluid (CSF) has been described as the central nervous system (CNS) equivalent of the complete blood count ( Jamison and Lumsden, 1988), and the analogy is appropriate. The “sink” action of the CSF arises from the restricted access of water-soluble substances to the CSF and the low concentration of these solutes in the CSF. The lymphatic function of the CSF is also manifested in the removal of large proteins and cells, such as bacteria or blood cells, by bulk CSF absorption. This capacity is important because the brain lacks a lymphatic system. The direct transfer of brain metabolites into the CSF provides excretory function. Acute or chronic pathological changes in intracranial contents can be accommodated, to a point, by changes in the CSF volume. Thus, the CSF protects the brain from changes in arterial and central venous pressure associated with posture, respiration, and exertion. The CSF is protective because its volume changes reciprocally with changes in the volume of intracranial contents, particularly blood. CSF provides a “water jacket” of physical support and buoyancy. CSF has four major functions: physical support of neural structures, excretion and “sink” action, intracerebral transport, and control of the chemical environment of the central nervous system. This chapter discusses the anatomy, functions, and biochemistry of cerebrospinal fluid (CSF).
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