1. Diseases Of The Choroid Plexuses

The choroid plexuses are subject to congestion, opacity, and thickening, and to a varicose state of their vessels: and these changes are mostly observed when the pia mater and arachnoid are in a similar condition. The choroid plexuses share more or less also in the processes of exudation, which arise from meningitis and acute hydrocephalus, and are then opaque, swollen, infiltrated, and covered with flocculent pseudo-membranous fibrin, or with purulent exudation.

Cysts and calcareous formations are the principal adventitious products in the choroid plexuses, and they are frequently met with.

The cysts, vesicles, or, as they are sometimes named, hydatids, of the choroid plexuses, are frequent and well known. Various misconceptions have prevailed as to their nature and cause, and undue importance has been attached to their presence. They have been taken for dilated lymphatic vessels, for enlarged capillary vessels (or terminations of arteries), and for new growths; and their value, in the scale of postmortem appearances, has been commonly over-estimated. They form bladders, sometimes with very thin, sometimes with pretty thick, vascular walls; they may be loose and pendulous, or filled and tense; they vary in size, equalling a poppy-seed, millet-grain, or bean; and when very numerous, they give the choroid plexus the appearance of a bunch of grapes. They occur only in the lateral ventricles, at least none that occur elsewhere are large enough to be detected in making the post-mortem examination with an ordinary amount of care, that is to say, none above the size of millet-seed. They occupy the convex portion of the plexus, especially towards the posterior cornu of the ventricle. They appear to me to be a disorder of the gland-like acini and villous appendages of the choroid plexuses, and, therefore, to bear a close analogy to the cysts, which are so often developed from the Malpighian bodies of the kidneys, especially in consequence of inflammation and Bright's disease.

In young persons they are almost constantly absent; but they are very frequent in those who are advanced in life, and in whom there is hydrocephalus arising from vacuum, or thickening and oedema of the inner membranes of the brain, etc.

These cysts, for the most part, have but one chamber, but they are often divided into compartments by delicate partitions. They generally contain a clear serum, but the fluid they enclose is often turbid, whitish, and like lime-water, and at last there is often whitish or yellowish bone-sand in them besides. These concretions incrust the cells, and are analogous to the sand met with in the brain; they are found, too, when there are no cysts, in the texture of the villi of the choroid plexuses.

Tuberculosis

This is an extremely rare occurrence: even when there is an exuberant production of tubercle in the tissue of the pia mater of the base of the brain, there is very rarely any trace of it in the adjoining choroid plexus.