Morphologic alterations associated with decreased cerebrospinal fluid pressure in chronic bovine hypervitaminosis A.

Arachnoid granulations and villi, choroid plexuses, and ependymal epithelium from 18 male Holstein-Friesian calves fed 108 (control), 8,800 (midly toxic), or 17,600 (severely toxic) mug of vitamin A/kg of live weight per day for 12 weeks were examined by light and electron microscopy for structural changes which could be used to explain the decreased cerebrospinal fluid (CSF) pressure seen in chronic hypervitaminotic A animals. In the toxic calf group, granulations were reduced to approximately two-thirds the size of those in the control calves, with the fibrous cap particularly being thinner and smaller. Second, height of epithelial cells of the lateral and 3rd ventricular choroid plexuses decreased significantly and that of the 4th ventricular choroid plexus, only slightly, as vitamin A intake increased. Structural differences of ependymal cells were not apparent between control and hypervitaminotic A calves. It is hypothesized that the thinner and less extensive fibrous cap of the arachnoid granulations in the toxic calves may result in increased permeability to CSF outflow.