Cerebrospinal Fluid

Abstract

As in the case of radionuclide studies in the evaluation of disorders of the brain, the introduction of computed tomography has resulted in a major reduction in the use of radionuclide cisternography. This method has been used in conjunction with clinical examination and other neurological procedures in children to aid in the evaluation of hydrocephalus. Radionuclide cisternography permits the observation of the mixing and absorption of the cerebrospinal fluid (CSF). Normally after the introduction of a tracer into the lumbar subarachnoid space, the material progresses rapidly upward so that at about 6 h the basal cisterns and Sylvian fissures are outlined and at 24 h the material is over the cerebral hemispheres or in the parasagittal region^10,11 (Fig. 14-1). The CSF is a secretion. Two processes, however, occur in series. There is filtration from the capillary lumen to the interstitial spaces of the choroid plexus, and that filtrate is the fluid from which the secretion is elaborated by the lining epithelium.⁴¹ The concept that CSF actually circulates in the spinal region with downward and upward currents of fluid may not be necessary, probable, or in any case the only mechanism that explains the movement of this fluid. It has been shown that with each pulse, about 0.75 ml of fluid from the cranium moves down into the spinal canal during systole and returns to the head in diastole. During this to-and-fro movement, mixing would occur and the kinetics of distribution of the tracer would be of the diffusional type and with a very high coefficient of diffusion.^12,41