Thomas H. Milhorat

Structure and Function of the Choroid Plexus and Other Sites of Cerebrospinal Fluid Formation

Publisher Summary This chapter discusses the structure and function of the choroid plexus and other sites of cerebrospinal fluid (CSF) formation. A considerable volume of the CSF is formed continuously within the cerebral ventricles. The choroid plexuses contribute to this formation, but a significant fraction of the CSF is formed extrachoroidally. The exact contributions of fluid from choroidal and extrachoroidal sites remain to be determined. The elaboration of choroidal fluid probably involves the following steps: filtration of the .blood plasma across fenestrated choroidal capillaries, formation of a protein-rich interstitial fluid within the choroidal stroma, and movement of constituents of the interstitial fluid across the choroidal epithelium by the combined processes of ultrafiltration and active transport. Contributing to the choroid plexus blood-CSF barrier are at least three specialized features: a system of circumferential tight functions joining adjacent epithelial cells; a heterolytic system of pinocytotic vesicles and lysosomes within epithelial cells; and a system of epithelial cell enzymes concerned with the active bidirectional transport of substances between the plasma and CSF. It is likely that the choroid plexus epithelium elaborates a carefully regulated fluid and, at the same time, participates in the homeostasis of the CSF. Evidence exists that the extracellular fluid of the brain is continuously formed across the cerebral endothelium, that it drains in bulk to the adjacent CSF cavities, and that it serves as a vehicle for removing intracerebral metabolites. Overall, there is probably a steady, net addition of new fluid at all points along the pathways of CSF circulation until the major sites of absorption (arachnoid villi) are reached.

Two Morphologically Distinct Blood-Brain Barriers Preventing Entry of Cytochrome c into Cerebrospinal Fluid

After intravenous injection, cytochrome c does not enter the cerebrospinal fluid. In most areas of the brain, the marker is prevented from leaving cerebral vessels by the capillary endothelium. In the choroid plexus, the marker passes freely out of capillaries into the extracellular space. However, it does not traverse tight junctions between epithelial cells and is rapidly incorporated into mnembrane-bound vesicles within the cell cytoplasm. Thereafter, cytochrome c is apparently removed by lysosomal degradation. These data suggest that there are at least two morphologically distinct blood-brain barriers to cytochrome c and that pinocytosis may be a mechanism for intracellular degradation rather than transcellular transport.

Nerve endings in the choroid plexus of the fourth ventricle of the rat: electron microscopic study.

Nerve fibers and nerve endings in the fourth ventricle choroid plexus of the adult rat were studied with the electron microscope. Nerve endings were found at two sites within the plexus: (1) on the smooth musculature of the blood vessels (i.e. vascular nerve endings), and (2) in the stroma between the choroidal epithelium and the fibrovascular core. Ultrastructurally all fibers were of the efferent type, and the majority were unmyelinated. No ganglion cell bodies were identified. Fibers ending in relation to the smooth muscle of the vessels presumably control the calibre of these vascular channels. Although the role of the stromal nerve endings is as yet unknown, these fibers may influence epithelial cell functions and thus indirectly regulate choroidal cerebrospinal fluid production.

Choroid Plexus Papilloma

An electron-microscopic study of a choroid plexus papilloma from the lateral ventricle of a child revealed fine structural features typical of normal choroid plexus tissue. Utilizing the Ernst techniq

Isotope Cisternography and Ventriculography in the Diagnosis of Hydrocephalus

Although isotope cisternography and ventriculography are by no means substitutes for air encephalography, they may provide useful additional information about cerebrospinal fluid flow and dynamics. Following the subarachnoid or intraventricular injection of a radiopharmaceutical, the tracer flows with the csf and demonstrates the pathways of circulation in a relatively dynamic way. The eventual distribution of the tracer is complex and is dictated in each case by the pathological and pathophysiological features of the given illness.

Expanding Ventricular Shunts for Hydrocephalus in Infancy and Childhood

Expanding, adult‐length catheters to accommodate continuing somatic growth have been implanted in the course of shunts, either to the heart or peritoneum, in 12 hydrocephalic infants and young children.