There may be General CBdema of the membranes and spaces, perhaps including the perivascular spaces in the brain substance. This sometimes takes place in Bright's disease, and may occur along with an oedema of other parts, or develop in a more isolated manner. The pressure of the fluid in this case was supposed by Traube to be the cause of the symptoms usually called uraemic, and in some cases it may contribute to the nervous disturbances of that condition, although not the chief cause.
Then there is an oedema ex vacuo. When the brain shrinks, as we have seen in General paralysis, or in Senile atrophy, there is a serious of substance. The loss of substance thus produced may be compensated for by thickening of the cranium or by augmentation of the cerebro-spinal fluid. Thickening of the cranium takes place only to a limited extent, and the space is chiefly filled up by fluid. The ventricles dilate (hydrocephalus), and the subarachnoid space is highly cedematous. It is to be particularly observed that there is seldom any excess of fluid in the subdural space, but that the soft membranes, especially between the atrophied convolutions, are highly cedematous.